Velocity vs. Accuracy - Sound Barrier

[wbond]

I'm a NOT a reloader, but I might have something to contribute that is worthwhile regarding accuracy and velocity.

There are other accuracy issues besides those I mention below, but what I say below is part of what makes or breaks accuracy.

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Bottom line: Keep your slower, heavier bullets 1050 fps or less muzzle velocity and your faster, lighter bullets above 1180 fps muzzle velocity, ideally above 1195 fps. Avoid all muzzle velocities between 1050 and 1180 fps, if you want good accuracy. Don't forget to take into account that the ammo maker probably used a longer test barrel. Alternatively, you can take the attitude the ammo manufacturer has, which is heck with it because handguns don't need to be that accurate.

I'll explain below.

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I have relatively little handgun experience, though I am not a novice. I have a lot of experience with .22 Magnum pellet guns (ya I said it), and with .22 Long Rifle and .22 Magnum firearms.

What in heck does that have to do with handgun accuracy? Everything because the velocities involved are similar and my pellet gun is a $400 RWS Diana that is more accurate than most .22 Long Rifles, at least to 65 yards.

Ballistics affect accuracy. Velocity affects accuracy. I'm not talking about bullet drop here, though it affects that too. I'm talking about the speed of sound and how the sound barrier affects accuracy in a negative manner.

Hi powered pellet guns and .22 long rifles have to be concerned with these issues because their velocities are near the sound barrier. The are either just below or above the speed of sound.

The sound barrier varies with temperature and elevation. Usually varies from 1080 to 1115 fps at common elevations and temperatures. For my purposes here I'm going to call the sound barrier 1100 fps because that's a common figure. When a projectile starts approaching the sound barrier the air starts bunching up in front of it and the turbulence increases right up to the point where the sound barrier is broken, which is the moment of violent turbulence (crack-bang).

When a projectile gets above approx 1050 it starts crowding the sound barrier a enough to cause turbulence that bumps the projectile off course a bit. It's like having a wobble in your steering. The closer the projectile gets to 1080-1100 fps the worse the turbulence, the more the accuracy deteriorates. That is why high-end pellet rifle manufacturers try to keep velocities below 1050 fps on most rifles, even if they have to use a heavier pellet to keep velocities down to 1050.

The turbulence starts to jostle the bullet and reduce accuracy the most above about 1060 or 1065.

The above was all in regard to object flying just below the speed of sound (heavier pellets from high powered pellet guns, heavier 40 grain bullets from .22 LR, and heavier slower pistol bullets. The heavier the bullet, the less the turbulence can affect it. i.e. - the greater the sectional density, the less turbulence matters.

For greatest accuracy, velocities must be kept below 1050.

However, to reduce bullet drop in rifles and to increase stopping power in rifles and pistols, a velocity increase is necessary. The question then is how to go super-sonic without losing to much accuracy? Simple, the greatest turbulence is just under the speed of sound (1060 to 1100) and just above speed of sound (1100 to 1120).

Just under the speed of sound the turbulence is bumping the front of the bullet. Just above the speed of sound the turbulence is bumping the rear of the bullet. At the speed of sound (commonly 1080 to 1100, sometimes up to 1115) the entire bullet is being bumped around by turbulence.

The trick to accuracy in a pellet rifle or .22 LR is either staying subsonic at 1050 or slower, or going super sonic and getting as far above the sound barrier as possible. i.e. - if you go fast enough you will break through the sound barrier so quickly and stay so far ahead of it that it doesn't have much time to affect your projectile.

What you want to avoid is staying close (just below or above) the sound barrer.

You especially want to avoid crossing the sound barrier twice (once during acceleration leaving barrel and again during deceleration downrange). Crossing the sound barrier twice means very bad accuracy.

By staying far enough below the sound barrier 1050 fps or less, you never get close enough to be affected much and never have to cross it.

If you want to go super-sonic for more energy or less bullet drop, then you need to get far enough above the sound barrier (1080 to 1100 commonly, sometimes up to 1115) that you cross it quickly and stay way above the speed of sound (way above 1115 fps) so your projectile doesn't catch turbulence from sound barrier.

Also, with super-sonic projectiles, you need to be far enough ahead of the sound barrier that you will stay above it down range. i.e. - you don't want the bullet to decelerate and get near or cross the sound barrier (a second time) before it hits the target.

For this reason, high-end pellet guns make a jump from 1050 fps with heavier pellets to 1250 with lighter pellets with no pellet weights-velocities in between. The idea is to either stay far enough below the sound barrier with a 1050 muzzle velocity, or stay way above it with a 1250 muzzle velocity with a lighter pellet.

Pellets have a very low sectional density and poor ballistic coefficient (not aerodynamic). So pellets decelerate much faster than pistol bullets. Pistol bullets decelerate much faster than rifle bullets.

The goal is to stay at least 30 fps below the sound barrier or at least 30 fps above the sound barrier at all times (even downrange). To stay at least 30 fps above at all times means that the downrange velocity must be at least 30 fps above the speed of sound (1115 + 30 = 1145 fps minimum acceptable downrange velocity at target).

For sub-sonic projectiles to stay below the sound barrier and still have decent killing power, the projectile must be heavy and large caliber. For super-sonic bullets to stay far enough above the sound barrier when downrange and have killing power, the bullet must be light or mid-weight and fast, which usually means a small to medium caliber. Only a magnum hand cannon can offer weight and high velocity, but the recoil is immense (like a .44 Mag). For manageable recoil you have to choose weight or speed. I like speed, but with as much weight as I can get and with 1150 to 1200 fps.

All this is very important to high power pellet guns that must hit targets 60 yds to 75 yds away. Also very important to .22 Long Rifle bullets. Because the .22 LR has a greater sectional density and a better ballistic coefficient (more streamlined), it is less affected by the sound barrier than a pellet. However, the .22 Long Rifle is used at longer ranges than a pellet gun. Often the .22 LR is used at 75 to 100 yds. So the affects of the sound barrier on accuracy over 75 to 100 yds are important. The .22 MAGNUM (firearm) rifle has a huge advantage over the .22 LR because the .22 MAG is way above the sound barrier both leaving the barrel (1800 to 2100 fps) and downrange at target. The speed of the .22 MAG is high enough to keep it far ahead of the sound barrier at all times, which is a big help at 100 to 125 yds both for bullet drop and accuracy.

How does this apply to handguns? The small caliber handguns I'm used to (.32 Mag and 9x18) lose about 50 fps over 25 yds. So the downrange velocity at 25 yds is 50 fps less than the muzzle velocity. This means muzzle velocity (if super sonic) needs to be high enough to keep the downrange velocity at least 30 fps above the sound barrier (1080 to 1115 with 1100 being most common).

i.e. - the minimum muzzle velocity of a super sonic handgun bullet should be 1100 + 30 + 50 = 1180 fps. Ideal muzzle velocity is 1195+. i.e. - 1195 fps or faster muzzle velocity is best for accuracy if dealing with super-sonic projectiles.

If the muzzle velocity is 1180 fps or faster, the bullet will usually be far enough ahead of the speed of sound to not be affected much by turbulence. i.e. - a supersonic bullet going 1180 fps or faster muzzle will be usually be accurate. However, higher elevations and/or higher temperatures can raise the speed of sound to 1115 fps (possibly higher). So to be really safe, the muzzle velocity should be 1200 fps or faster. The faster the better.

In other words, pellets and bullets with muzzle velocities of 1050 fps or less are the most accurate. 700 fps is the very most accurate muzzle velocity, which is why Olympic competition pellet guns have a muzzle velocity of 700 fps. However, good accuracy can be had up to 1050 fps muzzle velocity before needing to jump all the way up to 1200+ fps. That's why the most powerful hunting pellet rifles come in 1050 fps .22 caliber and 1250 fps .17 caliber versions. They don't make the .20 caliber mid caliber guns in the most powerful pellet rifles because the weight of the .20 caliber pellets would put their velocity right around the sound barrier. The .20 caliber pellet rifles are only offered in mid powered versions that don't have enough power to get near the sound barrier, but also don't have much hunting power.

Of the super-sonic bullets, as a general rule, the faster above the speed of sound you go, the better for accuracy. You need at least 1180+ fps muzzle velocity, but 1195+ fps muzzle velocity is best.

Muzzle velocities to avoid (if you care about accuracy): Avoid muzzle velocities between 1055 fps and 1180 fps. If you want to be a bit more liberal, then avoid those between 1060 and 1170 fps.

Also, you need velocity for stopping power. So if I were using a slower, heavier bullet; I'd try to get faster to be as close to 1050 fps as I could. Don't try to go faster than 1050, unless you can jump all the way to 1180+ fps.

If I wanted to use a faster, lighter bullet, I'd consider 1180 the bare minimum with 1195+ being ideal. The faster above 1180 fps the better the accuracy. However, bullets start fragmenting when velocities get to fast. How fast is to fast depends on your bullet, caliber, use, etc. However, I don't think you should have any fragmentation problems with good bullets from 1195 to 1300 fps.

That's why I prefer either a slower heavier bullet with 1050 fps muzzle velocity or a faster lighter bullet with 1195 to 1250 fps. I personally wouldn't go faster than 1250 fps muzzle velocity. I can also gain accuracy by having a heavier bullet with more sectional density and inertia. So in my opinion, if it's going over 1250 fps, I'd be looking for a heavier bullet to slow it down to 1250 fps muzzle velocity. Also, I think the bullet is less likely to fragment at 1200 to 1250 fps than at 1300+. That's why I think 1200 to 1250 fps is the ideal range of muzzle velocity, in my opinion. I realize that some cartridges can't do this. Many are to slow. Some are to fast. I think 1200 to 1250 fps muzzle velocity is ideal for the faster calibers. For heavier, slower calibers, 1050 fps is ideal. You don't have to agree, but that's my opinion.

If it's going under 1050, I'd be looking for a lighter, faster bullet to speed it up closer to 1050.

Of course, regarding bullet weights there are other issues such as caliber and sectional density that I won't go into further than to say that larger calibers offer greater sectional density, which helps accuracy.

To sum up: Slower and heavier bullets with 1050 fps muzzle or less are excellent for accuracy. Faster, lighter bullets going 1195+ fps are good for accuracy. I personally prefer the lighter faster option because I think it gives better stopping power, but that's just my opinion.

Slower, heavier bullets enjoy more sectional density and inertia which also help accuracy, plus they don't have to get near or cross the sound barrier. That's several advantages that make slower, heavier bullets more accurate, but I still prefer the ligher, faster option because that allows smaller calibers to have stopping power.

I personally prefer the heaviest, supersonic bullet that has from 1195 to 1250 fps muzzle velocity, if I can handle the recoil in that caliber. I consider 1225 fps muzzle velocity ideal. I like this combination because I think it's the best compromise of stopping power and accuracy I can get in a smaller (9mm) or mid-size (.40) caliber, plus bullets mushroom well between 1195 and 1250 and usually hold together too. This is one very good set of reasons why I like the .40 caliber S&W cartridge. However, I can't handle the recoil anymore (arthritis).

My next favorite is a 9mm Parabellum that has a velocity from 1195 to 1250 fps with whatever weight JHP gives that muzzle velocity. I think 1195 to 1250 fps gives the ideal combination of accuracy and stopping power with a recoil I can probably handle and bullets that mushroom and still hold together. 1225 fps muzzle velocity then should be ideal.

From purely an accuracy point of view, a subsonic 9mm would be best of the 9mms, but I've heard they have a poor history for stopping power, which makes sense because they lack the brute weight and diameter of a .45 and lack the shock effects of high velocity 9mms. Accuracy alone is not enough. Therefore the subsonic 9mm is not a good choice.

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I originally learned about accuracy and speed of sound from a pellet gun manufacturer.

I talked to an ammunition manufacturer about these issues and he said that he agrees these are important issues for pellet guns and .22 rifles. However, he thinks not very important for handguns since the combat range is usually 5-10 yds and a man is a big target. Therefore, handgun accuracy is not very important. Those are HIS words, not mine. He has a point from the typical combat point of view. However, I want all the accuracy I can get. I might want to shoot something at 25 yards or even farther some time, even if I am just plinking.

I'm not going to say which ammo manufacturer told me that because he's a nice guy and I don't want to embarrass him or his company.

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Speaking of cartridge manufacturers, they like to use longer test barrels then most people will ever use so they can inflate their muzzle velocity figures. Therefore, you need to figure out how much muzzle velocity your gun and barrel will give and use that for your muzzle velocity figure when shopping for ammo. I hope to buy a chronograph in the future. However, for right now, I have to use the estimate the ammo manufacturer gave me for my gun. He said that for a .32 Mag I can expect to lose approximately 33 fps per inch of barrel shorter than his 6" test gun. That's just an estimate. It's not really a straight line relationship, but his estimate is close enough for my gun. The best estimate for your gun will vary by caliber and other factors. If you don't own a chronograph, then you need to get a best estimate for your gun from a knowledgable reloader.

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Bottom line: Keep your slower, heavier bullets 1050 fps or less muzzle velocity and your faster, lighter bullets above 1180 fps muzzle velocity, ideally above 1195 fps. Avoid all muzzle velocities between 1050 and 1180 fps, if you want good accuracy. Don't forget to take into account that the ammo maker probably used a longer test barrel. Alternatively, you can take the attitude the ammo manufacturer has, which is heck with it because handguns don't need to be that accurate.

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What is the muzzle velocity and bullet type of the cartridge you are using? I suspect hollow points are more affected by sound barrier turbulence than a more sleek, streamlined bullet would be. However, JHPs are worth it. I also suspect boat tails are less affected by the turbulence of super-sonic flight. Super-sonic bullets have the greatest turbulence behind them because the sound barrier is behind them.

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I've read that some Finns pack vaseline into their hollow points to increase expansion and prevent the cavity from becoming clogged by clothing (such as denim). Supposedly, this works well for improving expansion. I wonder if it might help reduce wind drag or turbulence and increase accuracy? I'm considering trying this with melted beeswax, which would cool and harden. Perhaps the ammo manufacturers ought to do this with plastic? I know they do this for rifle ammo. Do they do it for pistol ammo?

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OK. Now I'm sure some of you guys are going to rip me up. Be careful this time because I can provide my sources for the speed of sound affecting accuracy of projectiles. I've been learning to expect a good b-slapping after opening my mouth. I'm ready this time. However, if you disagree, please keep it a friendly discussion with no personal attacks.

Thanks

 

[Khornet]

Er...not much new

the sound-barrier phenomenon is well known and accepted, far as I know. Probably explains some of the variation in accuracy with different brands of ammo for which .22s are famous: in some barrels one brand my stay comfortably on one side or the other of the speed of sound, while another stays too near it.

 

[Jim Watson]

The phenomenon is well known amongst target shooters.

You pretty well have to start subsonic for .22 lr and pellets because they are not powerful enough to stay supersonic all the way to the target, and are very sensitive to the Mach transition.

Long Range target rifles are loaded hot so they WILL stay supersonic all the way to the target, even at 1000 yards. This takes a big load in a .308, for example.

BPCR shooters toyed with the subsonic concept a while back. Black powder is not going to keep a lead bullet supersonic very far, so they thought they would be more accurate staying subsonic from the muzzle. Nearly all have gone back to traditional loads in the 1200-1400 fps range even though they drop subsonic on the way to the longer targets. The transition does not affect the big blunt bullets as much as it does a .22 lr or a jacketed spitzer, and overall wind deflection is reduced.

I doubt the effect is significant in a pistol, or is at least outweighed by other factors. Look at a revolver metallic silhouette shooter. He is surely using a Magnum with supersonic muzzle velocity dropping subsonic on the way to the 200 metre rams. Most conventional bullseye shooting is done with light loads and are never exposed to transsonic speeds. Is that to avoid the velocity range or is it to minimize recoil, or is it because best accuracy comes with less than maximum chamber pressure, or is it because the usual target pistol won't shoot supersonic velocity if you wanted to? But the recent success of the Beretta M9/model 92 in Service Pistol shows that a light fast bullet can be accurate, even though it is probably transsonic on its way to 50 yards.

 

[wbond]

Thanks

the sound-barrier phenomenon is well known and accepted, far as I know. Probably explains some of the variation in accuracy with different brands of ammo for which .22s are famous: in some barrels one brand my stay comfortably on one side or the other of the speed of sound, while another stays too near it.

To Khornet:

I'm glad you agree with what I said. However, there are a lot of people who don't understand those things and some ammo makers who don't care. Some do care. Winchester seems to be very good about this with regard to their 9mm offerings. Their Silver Tip has a claimed muzzle velocity of 1225 fps, which sounds great, though I don't know the length of their test barrel.

I have only talked to one ammo maker and looked closely at 3 others' loads. So I can't say how the other ammo makers are about these issues with their handgun loads.

My point is that a person needs to pay attention to the velocity figures before they buy because although you can't tell if a round will be accurate, you might be able to make an educated guess.

You obviously do understand these things, but a lot of handgun people don't.

Although the sound barrier issue is well accepted for rifles, it is not agreed on whether it matters for handguns. The only thing everyone seems to agree on regarding this issue and handguns is that it does NOT matter at 10 yards or closer. I do think it matters at 25 yards.

Do you think it matters at 25 yards from a handgun?

 

[wbond]

Good information

To Mr. Watson:

Your info sounds good. I'd like to add a few thoughts below.

I think that if the bullet is going to drop back to subsonic on its way to the target, then the closer to the target it is when that happens, the less it will affect accuracy.

One handgun ammo maker I talked to at length does not think this is a signifigant issue. His ammo's muzzle velocity from my gun he estimates to be 1100 fps (not good).

Three other handgun ammo makers I looked at apparently do think it's signifigant because their .32 Mag and/or 9mm handgun loads are all far enough below or above the sound barrier.

I think it comes down to how much handgun accuracy do you want at what distance? What max range do you want to be reliably accurate?

The ammo maker who told me it doesn't matter for handguns specifically said it doesn't matter at 7-10 yards, which he considers to be the range for self defense. Therefore, he doesn't think it matters. He never said it doesn't matter at 25 yards. I agree with him that it doesn't matter at 10 yards, but I think it does matter at 25 yards.

That's my opinion based on my prior experiences with .40 cal and current experiences with .32 Mag.

I agree with most of what you said, but I respectfully disagree with your statement that it probably does NOT matter for handguns.

I think it does matter at 25 yards, especially if the bullet exits the barrel at the speed of sound like that 1100 fps muzzle velocity load for my .32 Mag. There are also a lot of bad and good 9mm Para loads: really bad ones exiting muzzle right near the speed of sound (1080 to 1125 fps), slightly bad ones exiting muzzle at 1125 to 1160, good super soncic 9mm loads exiting muzzle fast enough above speed sound (1195+ fps).

The ideal velocity loads for .32 Mag, 9x18, 9mm Para, .40 cal, and others don't seem to cost any more than the less ideal ones. So why not buy loads more likely to be accurate?

Yes this whole topic is well known among target rifle shooters, which is where I learned it (from pellet target shooters). However, it seems to be less well known among handgun shooters, which is why I posted this. Another guy in another thread was asking questions along this very line. I answered him in that thread, but decided to start a thread about this as well.

Thank you very much for your input.

P.S. - Federal makes an excellent 85 gr JHP lower recoil load for .32 Mag that theoretically exits my gun about 1060 fps, which is good for accuracy. Stars and Strips makes a hot load 85 gr JHP for .32 Mag that theoretically exits my gun at 1160 fps, which is OK for accuracy. The other maker whom I won't mention exits my barrel at a theoretical 1100 fps, which I am NOT happy with. There are two good JHP loads for the .32 Mag. I just wanted to mention this so everyone would know the .32 Mag has good load options.

 

[Jim Watson]

It would take a pretty extensive test program to demonstrate the effect of transonic loading on pistol accuracy. Comparing catalog listings brand to brand of commercial ammunition does not convince me. Do you know they are shooting at their claimed velocities? Are they using the same brand and style of bullet? Too many variables. Maybe you could take up handloading, put your .32 H&R in a Ransom Rest and shoot the same bullet at narrow velocity increments.

I don't care enough to do the work. Most of my pistol ammunition is subsonic anyhow, that is inherent to .45ACP and I don't shoot many Magnums. I load 147 grain 9mm for the softer felt recoil; but I have had as good accuracy from mild 115 and 124 grain bullets in the velocity range you consider undesirable.

 

[JohnBT]

I only have this to add...



Notice the little cloud over the canopy.


"Condensation cloud as an F/A-18 Hornet flys at or near the speed of sound. Photo by John Gay."

 

[JohnKSa]

Your comments are all exactly correct, but I'll bet that a human can't shoot a handgun accurately enough from a standing position to note the effects of the perturbation caused by the transition from super- to sub-sonic velocities.

 

[grendelbane]

Well, you have explained why I load .45 ACP 230 grain to about 850 FPS, and 10mm 180 grain to about 1215.

My .38 supers with 147 grain bullets are indeed loaded to produce about 1050 FPS. They can go faster, but it takes quite a bit to get them over 1200 FPS. With 9x23mm, I can get them well over 1200 FPS. Need to do more experimenting.

In a nutshell, you have explained the popularity of the 10mm cartridge. It can launch an 180 grain bullet with the sectional density of the old 230 grain .45 loading, but it does so at a super sonic level.

You have also explained why my SIG P226 is so finicky when it comes to shooting accurately. It is one of the slowest 9mm's I have ever clocked. Most 115 grain loadings hit just over 1100 FPS, and group in a most mediocre manner. Hot +p does better, as do the 147 grain loadings.

Individual differences in individual guns can have their effects here.

 

[hurrakane212]

Thanks

This has been educational. I don't know if, when, or how much I will need this info but you never know... I am always gald to learn something new about guns.~Nathan

 

[unspellable]

There is a point not mentioned here. At subsonic speeds the drag on the bullet is proportional to the square of the speed. In the transonic region the function gets squirrely and involves the third power. At super sonic speeds it smoothes out and behaves again. This means that at transonic speeds the bullet has appreciably more drag than it does at subsonic speeds or at supersonic speeds just above tranasonic. The wind drift is proportional to the increased time of flight in air as compared to what it would be in a vacuum. (Not the total time of flight.) Hence the transsonic bullet displays more wind drift than a bullet just below or just above the transsonic region. I have always heard ths given as the reason for the standard velocity 22 LR rather than the turbulence in the transonic region.

 

[T.Stahl]

The sound barrier varies with temperature and elevation.

It is a common misconception that the speed of sound varies with temperature AND elevation/pressure or only the pressure. This probably comes from the many sources that say, "the speed of sound at sea-level is x mph, in the stratosphere it is y mph."

In fact the speed of sound c is a function of:
- kappa, the quotient of c_p and c_v, the specific heat capacities at constant pressure and constant volume
- R, the gas constant, which is the universal gas constant divided by the (average) molar mass of the gas
- T, the temperature in Kelvin

The speed of sound is calculated as:

c=sqrt(kappa*R*T)

For air (mainly a two-atomic gas) kappa is 7/5 and R is 287.1 J/kg/K.

And with a few conversions from Fahrenheit to Celsius to Kelvin and meters/sec to ftps you get:

__F___C_____K____m/s___ftps
-40 -40,0 233,2 306,1 1004,3
-30 -34,4 238,7 309,8 1016,2
-20 -28,9 244,3 313,3 1028,0
-10 -23,3 249,8 316,9 1039,6
0 -17,8 255,4 320,4 1051,1
10 -12,2 260,9 323,8 1062,5
20 -6,7 266,5 327,3 1073,7
30 -1,1 272,0 330,7 1084,9
40 4,4 277,6 334,0 1095,9
50 10,0 283,2 337,4 1106,8
60 15,6 288,7 340,6 1117,6
70 21,1 294,3 343,9 1128,3
80 26,7 299,8 347,1 1138,9
90 32,2 305,4 350,3 1149,4
100 37,8 310,9 353,5 1159,8

 

[wbond]

What matters to what?

I think we are all in agreement that these things matter to pellet guns and .22 rimfires, especially when target shooting, but also for hunting at distance.

The discussion issue is does the sound barrier matter to handgun accuracy?

Probably we can all agree that it does NOT matter at 10 yards.

I think the real question is does it matter at 25 yards? I think it does. What do you think?

Has anyone tested this? I just ordered a Shooting Chrony. So hopefully I will be able to look into this in the future.

Has anyone ever heard that temperature affects accuracy? I've heard that about rifles ever since I was a kid. Why does temperature affect accuracy? There might me more than one reason.

For one thing, the gun's metal would change size and properties a bit.

However, I think another issue is that substantial temperature changes cause substantial speed of sound changes. This would not be important if your gun shoots well below or above the normal speed of sound. I define normal speed of sound as (1080 to 1190 fps) because this is a common S of S range under common temp-elevation conditions. If your gun's muzzle velocity is near the normal speed of sound (1080 to 1190 fps), then a substantial change in temperature and/or elevation might put you at or near the speed of sound, which in turn would affect a rifle's accuracy. Would it affect a pistol? Yes, but probably not enough to care about, unless target shooting at 25 yds or farther.

Which brings me full circle. Do these things matter at 25 yards with a pistol? I think yes, especially if target shooting. Do they matter for self defense? No because that happens much closer than 25 yards (usually).

Thanks

 

[wbond]

How does humidity figure in?

To Stahl:

How does humidity figure in? Seems it would create more wind resistance and lower the speed of sound, but that's only a guess. Am I correct?

I'm not sure, but it sounds like you're saying elevation doesn't matter. Maybe I misunderstood you.

Both temperature and elevation matter because they affect air density, which in turn affects speed of sound. Is your entire chart based on sea level? At higher elevations the air is thinner, which I think makes the sound barrier at a higher speed.

================================

Less aerodyamic bullet shapes would be more affected by sound barrier. i.e. - this issue is more important to hollow points and semi-wadcutters than ball ammo. Ball ammo is sleek and aerodynamic, so it should be less affected. Yes, wadcutters were invented for target shooting, but that was intended for subsonic use. I think this issue is important for hollow points at 25 yards. Maybe even at 15 yards.

Based on my interpretation your data, we should avoid muzzle velocities from 1060 to 1210 fps. You've refined my earlier comment to avoid 1070 to 1195 fps. Based on your data, I'd now say avoid from 1060 to 1210 fps muzzle velocities.

1209 fps = 1159 + 50 The 50 fps is an estimated loss of velocity (JHP) occurring over 25 yards. i.e. - to stay super sonic all the way to 25 yd target, the muzzle velocity must be speed of sound + 50 fps (estimated).

I rounded to 1210 fps.

================================

Some cartridges are inherantly subsonic (.45 ACP), others transonic, others supersonic (.357M). Those that are inherantly subsonic would likely be most accurate. Those that are inherantly transsonic would likely be least accurate. The supersonic ones would likely be accurate enough. Personally, I prefer smaller supersonic bullets like some 110 and 115 grain 9mm loads because that gives stopping power from a smaller diameter bullet, which in turn allows a smaller gun that holds a lot of ammo. Of course there are other issues, such as I'm recoil sensitive, which is why I'm using a subsonic .32 Mag.

I think if you can combine good velocity with good sectional density and an appropriate rifling twist for bullet weight, you have the basic ingredients for great accuracy. If that can be done supersonic with a medium diameter bullet, then stopping power can be obtained from a compact gun that holds a lot of ammo. Two examples of this are the 9mm and 40 cal, but only if appropriate ammo used. Both of these cartridges have many good and bad ammo choices.

It is a common misconception that the speed of sound varies with temperature AND elevation/pressure or only the pressure. This probably comes from the many sources that say, "the speed of sound at sea-level is x mph, in the stratosphere it is y mph."

In fact the speed of sound c is a function of:
- kappa, the quotient of c_p and c_v, the specific heat capacities at constant pressure and constant volume
- R, the gas constant, which is the universal gas constant divided by the (average) molar mass of the gas
- T, the temperature in Kelvin

The speed of sound is calculated as:

c=sqrt(kappa*R*T)

For air (mainly a two-atomic gas) kappa is 7/5 and R is 287.1 J/kg/K.

And with a few conversions from Fahrenheit to Celsius to Kelvin and meters/sec to ftps you get:

__F___C_____K____m/s___ftps
-40 -40,0 233,2 306,1 1004,3
-30 -34,4 238,7 309,8 1016,2
-20 -28,9 244,3 313,3 1028,0
-10 -23,3 249,8 316,9 1039,6
0 -17,8 255,4 320,4 1051,1
10 -12,2 260,9 323,8 1062,5
20 -6,7 266,5 327,3 1073,7
30 -1,1 272,0 330,7 1084,9
40 4,4 277,6 334,0 1095,9
50 10,0 283,2 337,4 1106,8
60 15,6 288,7 340,6 1117,6
70 21,1 294,3 343,9 1128,3
80 26,7 299,8 347,1 1138,9
90 32,2 305,4 350,3 1149,4
100 37,8 310,9 353,5 1159,8

 

[wbond]

Hmm. Well I'm not so sure.

Your comments are all exactly correct, but I'll bet that a human can't shoot a handgun accurately enough from a standing position to note the effects of the perturbation caused by the transition from super- to sub-sonic velocities.

I don't know what the target shooting distances are at the Olympics, but I think they are well under 25 yards for most competitions. They consider these things very important and try to have their target pellet rifles shoot 700 fps. i.e. - they think it matters under 25 yards.

Now I realize that the typical pistol shooter wouldn't notice the difference at 10 yards, but I think it would be noticeable at 25 yards. It would defineately be noticeable beyond 25 yards. I've personally experienced a substantial difference at 50 yards with a .22 rifle and also with my high-end German pellet gun. With the pellet gun, the velocity is adjusted by choosing pellet weight, which is how all the websites devoted to pellet guns say to adjust the velocity of a one cock gun.

Anyhow, I do think it would be noticeable with a pistol at 25 yards, but would anyone besides a target shooter care? Maybe not. I'm a decent shot, but my cousin is scary good. He just yesterday put 4 out of 6 shots through the same hole at 15 yards with my .32 Mag. He doesn't even practice. He can use all the accuracy my Ruger .32 Mag can give and he would likely notice any difference. I'm not good enough to know if it's me or the ammo, but a great shooter like my cousin can make use of all a gun and ammo have to offer.

I estimate my Ruger .32 Mag gives 1050 fps muzzle with the Federal 85 gr JHP ammo my cousin used. Federal says 1100 fps from a 5" barrel, but my barrel is only 3". I'll know as soon as my Shooting Chrony arrives. I also read that the Federal target ammo for .32 Mag is heavier (95 gr) and slower at well below the sound barrier. I think Federal wants their target ammo sub sonic for a reason.

Anyhow, I think it does matter at 25 yards and farther for pistols. I think it might matter at 15 yards. That is my opinion.

 

[wbond]

Actually, that's all part of the same issue.

There is a point not mentioned here. At subsonic speeds the drag on the bullet is proportional to the square of the speed. In the transonic region the function gets squirrely and involves the third power. At super sonic speeds it smoothes out and behaves again. This means that at transonic speeds the bullet has appreciably more drag than it does at subsonic speeds or at supersonic speeds just above tranasonic. The wind drift is proportional to the increased time of flight in air as compared to what it would be in a vacuum. (Not the total time of flight.) Hence the transsonic bullet displays more wind drift than a bullet just below or just above the transsonic region. I have always heard ths given as the reason for the standard velocity 22 LR rather than the turbulence in the transonic region.

I agree with you completely. However, this is all related to the same issue. The speed of sound is a barrier that offers resistance when near it whether just below or above. The most resistance directly at the speed of sound. I used the term turbulence to describe this because the resistance is not steady. It fluctuates and doesn't always come completely head on. Sometimes the resistance is greater on one side of the bullet than another, which knocks the bullet off course a bit each time. Like small, localized, but powerful wind gusts.

In addition, the greater wind resistance near the sound barrier probably would make bullet more suseptable to cross winds. This is probably what you were referring to and I agree.

You've added to and strengthened my point, which is that transonic muzzle velocities and those near transsonic are undesirable. Also, supersonic muzzle velocities need to be fast enough to keep the bullet supersonic all the way to the target, which means speed of sound + 50 fps or faster for a 25 yard target.

The + 50 fps is an estimate based on what I observe to be typical for most 115 gr 9mm JHP (according to several manufacturers' velocity charts). This might be more or less than + 50 fps for other diameter-weight bullets. However, 50 fps is close enough to use for an estimate for most cartridges. If you want to be exact, a chronograph would tell the tale. At this time I don't have a chrono, but have ordered one.

One additional point: As you point out, there is more drag when transsonic. This causes faster velocity and energy loss. This is another good reason to not load bullets transsonic. This in addition to loss of accuracy.

So there are 3 good reasons to avoid transsonic speeds:

1) Less Accurate due to turbulence

2) More wind drift due to more wind resistance giving wind greater push on bullet

3) Rapid loss of velocity and stopping power due to greater wind resistance.

It appears to me that the case is getting stronger for avoiding transsonic bullet velocities.

 

[wbond]

To apply this Sound Barrier knowledge specific cartridges:

To apply this Sound Barrier knowledge to specific cartridges:

.32 ACP and .380: I have a soft spot for anemic mouse guns because they're easy to carry and don't hurt my recoil sensitive hands. The .32 ACP and .380 ACP are both anemic enough that the sound barrier is not an issue. They are strictly subsonic. I doubt they could ever get fast enough to be transsonic. However, I think the .380 can still get'er done in most cases. The subsonic velocities should theoretically give good accuracy, but these cartridges aren't known for accuracy. Why? Well for one thing these bullets are so light and short that the sectional density is pitiful. Also, the pocket guns aren't made for accuracy. However, I do get some amazing accuracy from my .32 Bersa-Firestorm and my CZ-83 .32 ACP (accurate for a .32 ACP anyway). Also, my CZ-83 .380 is darned accurate (for a .380). I don't yet own a Bersa .380, but everyone who does says they're very accurate (for a .380).

Bottom line for .32 and .380 ACP: they're subsonic with all JHPs, even with hottest loads. So don't even worry about the sound barrier or give a thought to velocity affecting accuracy. The only issue velocity has with these rounds it how it affects potential stopping power. Every little bit of velocity helps when you're underpowered and on the edge. Use whatever JHP is the heaviest that gives near 1050 fps muzzle. You probably won't get that fast, but come as close as you can.

.32 Mag: there is no point in my trying to use hot cartridges because those are transsonic and hurt my hands too. I'm better off to use something of normal power in my gun that will give a muzzle velocity of around 1050 fps from my 3" barrel with mild recoil. I'll just use the heaviest JHP that can give a muzzle velocity near 1050 fps. It's easy to choose .32M ammo because there are only two choices that offer about 1050 fps muzzle velocity from my 3" barrel: Federal 85 gr JHP and Black Hills 85 gr JHP. All other brands are transsonic from a 3" barrel and also kick like heck with lots of muzzle flash.

9x18: Same advice as for .32 Mag. Use the heaviest JHP that goes around 1050 fps muzzle. Good luck finding that in a JHP however. If you do find some, please let me know so I can buy some too.

9mm Para: The heavier subsonics (below 1060 fps) are accurate, but have a poor stopping power record. I think that's because they lack brute mass and diameter of a .45 and lack supersonic speed. i.e. - they have nothing to offer for stopping power, but are accurate. Transsonics offer decent stopping power, but not accuracy. The supersonic 110s and 115s should be OK for accuracy. They also have a good stopping power record. An example would be Winchester's 115 gr Silver Tip with muzzle velocity of 1225 fps from a 4" barrel. There was another brand (forgot brand) that offered 110 gr JHP with 1250 fps muzzle from 4" barrel. Those sound really good. These are normal pressure rounds. There were also a large amount of +P 115 and 124 grain JHPs with 1250 to 1300 fps muzzle, which sound good too. However, the Silver Tip 115 gr gives ideal performance with standard pressure. So why abuse the gun with +P?

.38 Special: That's a tough one. It's easy to be subsonic and accurate, but this only gives OK stopping power from this diameter bullet, in my opinion. It's easy to be transsonic, but that's bad for accuracy. It's best to be supersonic with this small diameter bullet, in my opinion. Unfortuneatly, supersonic .38 special loads are less common. However, there are a few 110 and 115 gr JHPs that offer good supersonic speeds. I'm not sure if all of them are normal pressure or +P, but it doesn't matter since all modern .38s handle +P fine. These light, supersonic .38 Special loads seem almost like 9mm in performance, especially if the revolver has a 4" barrel. A 3" barrel is also pretty good. A 2" barrel is going to be subsonic, but you can at least try to get up to 1050 fps muzzle.

For example, Corbon makes a +P .38 Spl 110 gr JHP with 1250 fps muzzle with a 4" barrel. It gives 1050 fps from a 2.5" barrel. All this according to Corbon.

Note: Normally, I don't like +P ammo because it's hard on guns and hands. As a general rule, if you need +P, then you should upgrade to a more powerful chamboring. However, I think .38 Spl is an exception because all modern .38 Spl revolvers can shoot +P all the time. This is especially true of Rugers. I don't recommend +P+ for anything.

.357 Mag - this is an easy one. It should be very easy to stay supersonic here. I've read that the 125 gr JHP has the best .357M stopping power record. That makes sense because when dealing with a smaller caliber (under .40), you have to get your smack down from velocity, but still need enough weight for penetration. The 125 gr JHP .357 Mag gives plenty of both and should be accurate too.

I like that. I'm not going to say "stopping power" any more. I'm going to say "smack down".

.40 cal: This is a tough one, but can be very good. The 180 grains are subsonic and accurate, but they have a mediocre stopping power record. The 155 to 165 gr bullets have good real world stopping power records, but most are transsonic and not accurate, in my experience. However, there are a few 150 to 165 gr JHPs that are adequately supersonic (Corbon and Winchester Silver Tip to name two). Theoretically, these should be all around fantastic due to supersonic with good weight and sectional density, which in theory combine for good accuracy and stopping power. The 135 grain JHPs are very supersonic, which gives theoretical decent accuracy; they also have the best real world stopping power records. However, I wonder if a 135 gr .40 cal bullet has enough sectional density to be accurate? Does it? Maybe. I don't know. Never used one. Personally, I think a 140 to 150 grain JHP would give the best combination of supersonic velocity and sectional density for this caliber. Does anyone make a 140 or 150 JHP that is adequately supersonic?

I used to own a .40 Glock for years. I loved it, but it was never accurate. I only shot transsonic 155 gr JHPs of different brands because I didn't know any better. I shoot way better now with my CZ-83 9x18 and Ruger .32 Mag, even though I'm very handicapped now. I wish I could try 135 gr JHPs in a .40 cal Glock to see if accurate, but my hand won't tolerate a .40 cal anymore. Maybe someone else could try this and let me know?

.44 Special: This is strictly a subsonic cartridge as far as I'm aware. Ahhh, the simplicity of no choices. No transsonics to avoid. No superonic choices either. Subsonic simplicity with high sectional density and accuracy galore and a large diameter bullet.

.44 Magnum: I'm not very familiar with this cartridge, but just for this post I went to Winchester.com and PMCAmmo.com and looked at some of what they had. I see transonic rounds I'd avoid. However, these transsonic rounds are so heavy and have so much sectional density that they can probably shrug off most of the sound barrier turbulence. I also see many supersonic choices. I also went to PMC and saw a lighter, VERY super sonic choice. I don't know if subsonics are even an option here. If subsonics are available, why use them when there's so many good supersonic loads available? If it were me, I'd choose a supersonic load and avoid all transsonics.

.45 ACP - most rounds are very subsonic. So the sound barrier issue probably doesn't affect most .45 ACP owners. However, manufacturers do make some lighter, faster .45 rounds. In theory, they should be accurate if they stay 1050 fps or less or above 1210 fps. Of course the lighter rounds have less sectional density, which also matters. I'd be curious to know if anyone has tried lighter, faster .45 JHP rounds. If so, what was the muzzle velocity and how accurate was it? I'm not that familiar with .45 ACP, but I think I'd want to go 1050 fps with whatever bullet weight does that.

 

[wbond]

Typo Correction and Revision

In my original post, with regard to subsonic bullets:

I said, "If it's going under 1150 fps, I'd be looking for a lighter, faster bullet to speed it up closer to 1150." That's a grevious typo.

I meant to say, "If it's going under 1050 fps, I'd be looking for a lighter, faster bullet to speed it up to approx 1050 fps." That applies to subsonics.

==========================================

For supersonics: If it's going over 1300 fps, I'd be looking for a heavier bullet to slow it down closer to 1250 to 1275 fps.

1300 fps is still fine as long as the bullet weight is heavy enough to have good sectional density.

==========================================

To revise my earlier post about what gives ideal accuracy at 25 yds and farther:

Ideal for subsonic bullets is the heaviest bullet that will fly from muzzle at approx 1050 fps.

Ideal for supersonic bullets is muzzle velocity between 1210 and 1275 fps using whatever JHP bullet weight provides the best sectional density for the caliber.

If the caliber involved has a hard time getting to 1210 fps muzzle velocity with a bullet weight that offers good sectional density, then 1200 fps muzzle velocity is good enough. If you can't make 1200 fps, then go with a way heavier bullet at 1050 fps.

I prefer standard pressure loads if they can get it done. Why abuse your gun with +P if you don't need to? The exception is .38 Special because +P is often needed to attain decent performance and all modern .38 Spl guns are made for +P. Corbon makes a .38 +P that offers a 110 JHP with 1250 fps muzzle velocity. Wow.

I don't recommend +P+ under any circumstances for any cartridge or gun.

 

[unspellable]

humidity

A water molecule has less mass than an oxygen or nitrogen molecule. Hence higher humidy results in lower sir density and less drag. (Also less engine power and less lift, increasing an airplane's take off distance.) So with higher humidity there would be less velocity loss. Not sure what this does for the speed of sound.

 

[wbond]

That seems counter intuitive.

I'm not disagreeing because I don't know. It just seems what you said is counter intuitive. Water in the air is extra matter in the air. Wouldn't that mean more molecules a flying object has to plow through? i.e. - more drag?

You are saying water vapor is less dense than air. Is that correct?

I'm going to knock off for now. I'll check back tommorrow. Thanks.

A water molecule has less mass than an oxygen or nitrogen molecule. Hence higher humidy results in lower sir density and less drag. (Also less engine power and less lift, increasing an airplane's take off distance.) So with higher humidity there would be less velocity loss. Not sure what this does for the speed of sound.

 

[unspellable]

water vs air

Yes, water in vapor form is less dense than air. No water doesn't displace air, it's simply part of the air. The percentage varies from time to time, but then so does the smog in LA and that's part of the air too.

The drag of an object moving through the air can be modeled in various ways. One way to think of it is that the object must knock an air molecule out of its way. Think of a cannon ball knocking a BB out of its path. The cannon ball must give up some small energy to deflect the BB. The more the BB weighs, the more energy required to deflect it.

The total number of molecules in the path of an object depends much more on the air pressure than on the air's exact composition.

 

[JohnKSa]

They consider these things very important and try to have their target pellet rifles shoot 700 fps. i.e. - they think it matters under 25 yards.

The typical distance is 10m for airgun target shooting so you're definitely right on the "under 25 yards" bit. I agree 100% as this applies to airguns. I think picking the muzzle velocity is critical to airgun accuracy since the pellets are much less aerodynamic and much lighter than bullets.

I think you're probably right about very long-range handgun shooting, (well beyond 50 yards) but I wonder about typical handgun shooting (inside 50 yards). I intentionally phrased my comment in the form of a bet, rather than as a statement of fact, because I have no information to contradict you. However, my intuition, (such as it is ) backed by a total absence of commentary on this topic as it concerns centerfire handgun target shooting, still leans strongly toward it being a very small contributor.

It would make an interesting experiment. If you are going to test it, I'd suggest using a pistol caliber carbine shot over a rest in order to eliminate the issues of trying to get precision accuracy from a handgun.

 

[wbond]

How about a lighter faster .38 Super?

You should have no problem going supersonic with a lighter .38 Super bullet.

For example, how about a 115 gr JHP bullet?

A 9mm Para can get a 115 grain bullet to 1225 fps with normal pressure, or over 1300 fps with +P. So surely a normal pressure .38 Super could get well over 1210 fps muzzle velocity with a 115 gr bullet.

For supersonic accuracy, you need 1210 fps or more muzzle velocity, but for stopping power 1250 fps to 1275 fps would be awesome and maybe even more accurate.

You might also try 124 grain bullets.

Just forget about 147 grain bullets. That is to heavy for this caliber, in my opinion. Also 147 grain is too slow, unless really hot loaded.

Well, you have explained why I load .45 ACP 230 grain to about 850 FPS, and 10mm 180 grain to about 1215.

My .38 supers with 147 grain bullets are indeed loaded to produce about 1050 FPS. They can go faster, but it takes quite a bit to get them over 1200 FPS. With 9x23mm, I can get them well over 1200 FPS. Need to do more experimenting.

In a nutshell, you have explained the popularity of the 10mm cartridge. It can launch an 180 grain bullet with the sectional density of the old 230 grain .45 loading, but it does so at a super sonic level.

You have also explained why my SIG P226 is so finicky when it comes to shooting accurately. It is one of the slowest 9mm's I have ever clocked. Most 115 grain loadings hit just over 1100 FPS, and group in a most mediocre manner. Hot +p does better, as do the 147 grain loadings.

Individual differences in individual guns can have their effects here.

 

[Michael Courtney]

BPCR shooters toyed with the subsonic concept a while back. Black powder is not going to keep a lead bullet supersonic very far, so they thought they would be more accurate staying subsonic from the muzzle. Nearly all have gone back to traditional loads in the 1200-1400 fps range even though they drop subsonic on the way to the longer targets. The transition does not affect the big blunt bullets as much as it does a .22 lr or a jacketed spitzer, and overall wind deflection is reduced.

A shotgun slug is a lot like a big blunt bullet, but I have seen the sonic transition completely ruin the accuracy of the lightfield sabot slug shot from a rifled barrel. Accuracy is great at 100 yards (2 MOA), but is horrible at 150 yards (6 MOA). With the relatively low BC of the Lightfield slug, the sonic transition occurs at about 125 yards. Most other sabot slugs have significantly higher BC's and remain supersonic out to longer ranges.

Michael Courtney

 

[Michael Courtney]

Do you think it matters at 25 yards from a handgun?

Not usually. Anything that affects the accuracy of a bullet does so by changing the direction of the bullet. There needs to be some distance _after_ the bullet changes direction for a bullet's change in direction to affect accuracy.

Think about shooting through a bush. If the target is right behind the bush, you'll pretty much hit what you're aiming at in spite of the bullet's change in direction while penetrating the bush. However, if the target is 25 yards past the bush, odds are you are going to miss.

So whether or not the sonic transition affects accuracy at a given range depends on how far beyond the transition range the target is located. Most handgun loads aren't going to have sonic transitions close enough to the muzzle to impact accuracy at 25 yards.

Michael Courtney