Barrel length vs power in a springer

[Chevota]

I have a couple questions about barrel length vs power in a typical break-barrel springer, coil or nitro, doesn't matter.

Basically has anyone tested various barrel lengths with one gun, or noticed an pattern of power loss with shorter barrels?

Also, I know the TX200 has a shorter than normal barrel and I'm curious if anyone who owns one can give me a real #? I don't mean overall length, but the actual rifled part that the pellet makes use of.
I was corresponding with someone about it and they claimed it was 9". I thought/assumed it was closer to 15. I also believe there are two different lengths, one being a shorter carbine. Can anyone clarify their length and if it's a std or carbine? And please don't quote the mfg's specs, but actually measuring their barrel.

I personally have seen a loss in power with reduced barrel length in springers, for example a generic 18ftlbs .177 springer with an 18.5" barrel losing about 1ftlb per inch of barrel length removed. I haven't gone shorter than 13" which put the guns below 13ftlbs, but before I sacrifice a barrel I'd like to get input from others who have seen similar results using shorter barrels, carbine, cut, whatever.

The guns I used for my testing were standard Crosman break-barrel with both coil and nitro springs. I have mainly tested .177 which needs more length than .22, but I have also noticed a slight drop in .22 when going from 18.5" barrel to 17.3". Not nearly as much as a .177, and sometimes almost nothing at all which leads me to believe an 18ftlb springer in .22 only needs ~17.5". It also makes me wonder what the ideal length (for power) is in .177 at 18ftlbs, and how that would change as power went up, say 25ftlbs? I'm tempted to try a longer barrel for an 18ftlb .177 Crosman, such as a magnum barrel of over 19.5", but that's a lot of work so I thought I'd see if anyone has experience with this first.

Thank you in advance for your time..
Chevota

 

[JohnKSa]

This is an interesting topic. I've seen some evidence that in some cases, going to a shorter barrel can actually improve velocity because it decreases friction, AND because as the piston rebounds, it can, in extreme situations, cause a vacuum that can slow the pellet.

 

[rcmodel]

That all sounds reasonable to me.

Piston air-guns are not dependent on barrel length like firearms needing a certain barrel length to complete the powder burn curve.

If the spring-piston volume is designed correctly for the barrel length?

Not much else but velocity loss can happen after the volume of high pressure air runs out, and pellet friction takes over.

rc

 

[RussB]

double tap

 

[Pete D.]

Barrel length

A break barrel spring gun......the pellet achieves max velocity in the first six to ten inches of the barrel. If you see a difference in velocity between barrels that are longer than that, then something else is happening.
The most important functions of barrel length past six/eight inches are sight radius and the fact that the barrel is also a lever used to cock the gun....longer levers are easier to move.

 

[230RN]

It's long been known that about an 18" barrel gives the highest velocity in .22 standard velocity rounds. Beyond that, as has been pointed out, the remaining volume and pressure behind the bullet is not sufficient to accelerate it any more.

 

[Mousegun]

http://www.mediafire.com/view/5mcemcyutrm/The+Air+Gun+From+Trigger+To+Muzzle_s.pdf

 

[ChaoSS]

It's long been known that about an 18" barrel gives the highest velocity in .22 standard velocity rounds. Beyond that, as has been pointed out, the remaining volume and pressure behind the bullet is not sufficient to accelerate it any more.

You talking rimfire? Or pellets?

Chevota, Tom Gaylord did a blog about the Tx 200, i want to say about 2 weeks ago. Might want to ask him about the specs on it.

 

[RussB]

There are several factors involves in getting maximum efficiency out of a give airgun,

The available air chamber volume
The spring's power
The transfer port
The weight of the pellet
The quality of the barrel
The choke on the barrel

As Pete says, break-barrel springs need a longer barrel to give you enough leverage to cock the spring, and more powerful the airgun, the more leverage you need

I have an R9 with a 16.6" barrel and a HW97k with a 10" barrel. Both tuned with Maccari springs & seals.

The R9 shoots 911 fps with Crosman Premier Lite (8.0 grains), and the HW97k shoots 912 fps with the CPL's

R9 with JSB Exacts (8.4gr) 890 fps
Hw97k w/JSB, 890 fps

What does this tell me regarding the barrel lengths effect on velocity? Nothing. The guns power plants are similar but still different enough to skew the effect of barrel length on velocity

 

[230RN]

"You talking rimfire? Or pellets?"

Rimfire, sorry. I threw that in there as a response to another post, in order to show that it is well known that there was a maximum barrel length for maximum velocity. This, regardless of the type of gas behind the projectile.

I should have been more specific.

Terry, 230RN

 

[Chevota]

Thanks for the replies guys.
Yes I've heard the story of the pellet peaking at 6" which is also mentioned in the pdf guide Mousegun kindky posted, but it is dated and doesn't apply to today's airguns. Just like a firearm with a larger powder charge needs a longer barrel to hit peak power, an airgun with 18ftlbs needs more barrel than a 4ftlb gun that peaks at 6".

I'd love to test a variety of guns, but I'm not willing to chop up anything except a Crosman barrel. I understand that the bore and stoke are a factor, as is piston weight, spring strength, and other things. I think a standard Crosman has great specs for testing because it makes outstanding power for its chamber volume and cocking effort. Its specs are close to a TX200 or HW97 which are both lower powered, and imo it's due to their shorter barrel. I can't really say since they are different like Russ said, all I can say for sure is a .177 Crosman will lose power steadily as the barrel length is reduced.

So per Russ the HW97k has a 10" barrel... Interesting, and I wonder they made it so short? Hopefully someone with a TX200 will chime in too, I'm still curious to see if they really have a 9" barrel, and if that is the carbine version or not... I suppose the Euro guns need to consider the 12ftlb rule, but I'd reduce spring pressure, not barrel length. Or maybe they do this to make it impossible for people to increase power and break the law?

 

[JohnKSa]

I can tell you that based on the physics of spring-piston airguns, the pressure drops off VERY rapidly after it spikes.

1. The piston rebounds (to some extent) after achieving peak pressure and that causes a very rapid drop in pressure. In some cases that can actually generate a vacuum in the barrel. The Cardews managed to document that in some unusual situations that vacuum can even draw the pellet back into the compression chamber.

2. The very high amplitude of the pressure peak is the result of the fact that rapidly pressurizing a gas also raises the temperature which in turn raises the pressure even higher, raising the temperature and so on--a feedback situation. That means that you get a lot higher pressure due to the rapid pressurization that the piston's abrupt movement generates than you would if you gradually compressed the same initial volume of gas into the same final volume.

But when the pressure starts to drop the process works in reverse. The temperature drops and that drops the pressure more--exactly the same feedback situation but in reverse. So there's a very high pressure peak to get the pellet moving, but that pressure comes back down very fast once the pellet begins to move--leaving very little volume of gas to push the pellet down the barrel.

So the situation is VERY different from a firearm, or even a PCP/pump airgun where you have an expanding volume of gas pushing the projectile down the barrel. In a firearm, the gas is actually being generated by combustion for most, if not all of the duration of the projectile's trip down the barrel. In a PCP, there's a considerable amount of air compressed into a small volume--sufficient to keep expanding for most of the pellet's trip down the bore.

In springers, the actual volume of gas being compressed is quite small compared to a PCP or a pump airgun. The pellet gets an initial "boot" from the tremendous pressure spike but then the pressure drops off very rapidly because there wasn't much volume of gas to begin with.

The initial push can be quite violent--to the extent that it often deforms the skirt of the pellet dramatically which can be observed in recovered pellets. But after the initial push, there's not much pressure pushing the pellet down the bore--and in extreme circumstances, there may actually be no pressure at all, or even a vacuum at some point before the pellet exits.

There are obviously a ton of variables involved, including the bore volume, the pellet weight, bore friction, spring force, piston friction, piston rebound, swept volume, venturi dynamics, etc., but that's the basics of the problem as I understand it.

The Cardews wrote an excellent book "The Airgun from Trigger to Target" that covers the math and science in more detail than most people care to know. It's worthwhile reading for anyone with a strong interest in the topic.

 

[ChaoSS]

Thanks for the replies guys.
Yes I've heard the story of the pellet peaking at 6" which is also mentioned in the pdf guide Mousegun kindky posted, but it is dated and doesn't apply to today's airguns. Just like a firearm with a larger powder charge needs a longer barrel to hit peak power, an airgun with 18ftlbs needs more barrel than a 4ftlb gun that peaks at 6".

I'd love to test a variety of guns, but I'm not willing to chop up anything except a Crosman barrel. I understand that the bore and stoke are a factor, as is piston weight, spring strength, and other things. I think a standard Crosman has great specs for testing because it makes outstanding power for its chamber volume and cocking effort. Its specs are close to a TX200 or HW97 which are both lower powered, and imo it's due to their shorter barrel. I can't really say since they are different like Russ said, all I can say for sure is a .177 Crosman will lose power steadily as the barrel length is reduced.

So per Russ the HW97k has a 10" barrel... Interesting, and I wonder they made it so short? Hopefully someone with a TX200 will chime in too, I'm still curious to see if they really have a 9" barrel, and if that is the carbine version or not... I suppose the Euro guns need to consider the 12ftlb rule, but I'd reduce spring pressure, not barrel length. Or maybe they do this to make it impossible for people to increase power and break the law?

http://www.pyramydair.com/s/m/Air_Arms_TX200_MkIII_air_rifle/174

PA lists barrel lengths. 9 inches.

 

[Chevota]

I've read Trigger to Muzzle a while ago, then the Trigger to Target the past few days looking for better info, but I didn't find anything. It still looks like the belief a pellet hits peak velocity at 6" is based on ancient writings of an ancient gun making 4ftlbs which I've long since known wasn't true for more powerful guns. I disagree with other things as well, such as their claim that the burning oil makes more than 50% of the guns power which I have also tested and is 100% false. It seems these are the only books out there so people accept them as fact, maybe because it looks legit with all the pictures and graphs and such. People will argue until blue in the face that the books are fact and nothing will change that. All I say is test it yourself, and as far as I know not one person aside from myself has done that. I'm looking for them tho....
It's ok, I will cut a spare barrel and compare my old results, then go beyond 13" all the way down to 6", for as they say "the halibut."
I'm still curious about the TX200 barrels length, and why it and the HW97(k) barrel is so short. I can't add a longer barrel to one, nor would I so we'll never know what those guns are capable of. I know they will never have the power of a generic Crosman so I'm sure they are better off with a shorter barrel, but not that short. Their bore and stroke is imo better suited for a shorter barrel as well, but only slightly, and I still firmly believe they'd both benefit by 15" or so in .177. Just my opinion tho, and since nobody will test it I guess we'll never know. Well, Weihrauch and Air Arms knows the truth but I doubt they'll share.
ChaoSS: I've seen 9", 10", and 15" listed which is why I asked for a real measurement on a real gun in my first post. Advertised specs can be very frustrating! In the picture it's clear the outside of the barrel is at least 15", but what's inside?

 

[JohnKSa]

I think that their testing and conclusions were reasonable as far as they go. Trying to take their testing results and apply them without modification or qualification to every airgun currently available will certainly result in contradictions and misnomers.

I can tell you right now that anyone who says that "a pellet hits peak velocity at 6 inches" and doesn't qualify the statement further is mistaken or attempting to mislead. Even if they accurately tested the statement in a particular gun, without further qualification the statement is still incorrect since different pellets would certainly change the results.

If you're trying to prove or disprove unqualified statements like "a pellet hits peak velocity at 6 inches", you're wasting your time. The huge number of contributing variables/factors will make it impossible to come up with a single number that works in the general case. In other words, even without testing, it is easy to see that the statement is untrue, and no amount of testing will be able to boil a complicated problem like this one down to a single-number result.

I can tell you that the data on the Pyramyd website indicates that the .22 TX200MKIII's has a 15fps velocity advantage over the .22 TX200HC using the same weight pellets. The problem is that unless they tested a number of each of the guns and averaged the velocity results, you could be seeing the result of individual variation, as opposed to the effect of the 3" longer barrel in the TX200MKIII. Especially since the difference is so small.

 

[Chevota]

You might be reading too much into this, I'm just looking for some info people might have. I agree that the 6" rule probably was correct with their extremely weak gun back in 1970, but many people believe this rule is written in stone and I assume this book is why they think that. I already know it's not true, and to be honest I don't feel like cutting a barrel down to 6" to prove it because I already know what will happen. I am curious, but I'm fairly certain it'll turn an 18lb gun to 6lb +-2.
I still haven't found out how long a TX barrel is, but finding out an HW97k is only 10" (per Russ) is surprising to me. They must have a reason but I can't imagine what it is. The 97k makes a lot less power than it could (imo), but it does make more than I would have guessed, and why is something I'd like to know.
So I'm looking for any info on different barrel lengths on the same gun, anything at all with velocity comparisons to get a better feel for all this. That and the length of a TX200 barrel, and if a carbine TX200 exists what is its length. I'm not looking for anything more than that, nor am I interested in arguing about whatever.

 

[JohnKSa]

As nearly as I can tell, the standard TX200 barrel is about 12" (rifled length) while the carbine barrel is about 9" (rifled length). The overall barrel lengths are about 4" longer for both, with the additional 4" of length being shroud length which shouldn't affect velocity one way or the other.

According to the Pyramyd air website, the velocity difference is about 15fps in .22 caliber with the advantage going to the longer barrel. About a 4% drop in energy from a barrel length reduction of 25%.

I'm fairly certain it'll turn an 18lb gun to 6lb +-2.

It seems likely you'll lose some energy, but I would be very surprised to see energy drop by a factor of 3.

They must have a reason but I can't imagine what it is. The 97k makes a lot less power than it could (imo), but it does make more than I would have guessed, and why is something I'd like to know.

Understanding how the powerplant works should make it pretty clear that you're not gaining a lot of velocity after the initial "kick" due to the rapid pressure/temperature drop once the pellet begins to move and the piston rebounds.

Alternatively, you might try comparing the volume of air used to push a PCP pellet at a given velocity with the swept volume of a high-powered springer that will manage the same velocity. The results should be pretty revealing.

I personally have seen a loss in power with reduced barrel length in springers, for example a generic 18ftlbs .177 springer with an 18.5" barrel losing about 1ftlb per inch of barrel length removed.

Could you explain how you performed this experiment?

Did you actually take a gun, test it, cut an inch off the barrel and retest it and repeat?

 

[Chevota]

Yes I cut a barrel down. Tests were done with a Benj Titan, Crosman G1, and Stoeger X20S. The X20S is why the length issue started, they have a short barrel which made a huge power loss.
Yes I fully understand springers, PCP, firearms etc.
You can't trust the specs given on websites that sell guns, not even close.
So are you curious or looking to put me down? I ask because usually when someone replies the way you have with quotes and asking for specifics they're only looking for a way to insult. The barrel thing isn't in question, I know it costs power, I'm just looking for info others may have to help me get a better feel for this because I'm not going to cut up a bunch of barrels. I'll do the Crosman because I have spares I'll never use, but that's it. All other info needs to come from others such as std vs carbines etc or I'll just have to do without. The HW97k power to barrel ratio was interesting, but I'd need to get my hands on one to see why, if I asked on a forum I know exactly what answers I'd get and none would be why.

 

[JohnKSa]

So are you curious or looking to put me down?

Curious. As I said in my first post, this is an interesting topic.

I quote what I'm responding to in the interest of clarity so that it is easy to tell what I'm responding to.

The reason I asked about the specifics of the test methodology is because there are a number of ways the test could have been conducted and the specific way it was conducted bears heavily on the value/interpretation of the data collected.

I'm still not quite following your explanation of the test. You say the testing was done with 3 different guns but you also seem to say you only cut one barrel down. Did you figure out a way to install it on the different guns and do measurements as you cut it down?

You can't trust the specs given on websites that sell guns, not even close.

In this case, the two figures are chronograph data with the pellet weight specified, not manufacturer provided data. Pyramyd provides measured data for some of the guns they sell, and makes it clear when the data is measured by them. The reason I only provided data for the .22 version of the gun is that their specs for the .177 versions of the two guns are manufacturer provided and therefore nearly meaningless, as you say.

The figures also agree well with data I've seen elsewhere from the TX200 guns, so I'm reasonably confident that they are representative. At any rate, for the moment, they seem to be the only ones available.

 

[Chevota]

I still suspect I'm being baited because this mirrors past experiences, but I'll give you the benefit of the doubt.
Ok, yes, one generic Crosman barrel (open sight, I think from a Rem Vantage) was put on a Titan, G1, and X20S. No figuring needed, they bolt right on in seconds. I have spares because I upgraded barrels and/or changed caliber on most Crosman guns I've had. I used the Titan and G1 because they were good test beds for a variety of tests I did at the time, one nitro, one coil, and making about 18.5ftlbs which varied with pellets and caliber.
It all started with a Stoeger X20S I bought which made a pathetic best of 10.2ftlbs unmodified. This is when I discovered the barrel was only 13", something they don't advertise. After tuning (and finding nothing wrong with it) it was a little higher, then adding a nitro for a peak of 12.4ftlbs (12.9lbs using Gamo Raptor which I consider cheater pellets). I also tried the 18.5" barrel from the G1 to verify the Stoeger power plant was working correctly. The Stoeger is for the most part identical to Crosman so it's easy to compare. I can’t put the X20S barrel on the Crosman guns because it’s too wide, so the only way to test the Crosman guns was to cut a Crosman barrel. I cut the barrel to 16" (I already knew what 17.3 did), then I cut it to 13". I tested it on the Crosman guns and the X20S to verify it matched the S barrel, otherwise I’d never know if the S was defective. Some barrels have too much friction or other problems which can cost 1-2ftlbs.
I liked the S barrel because it was quiet and I wanted the gun for a special use, but I can make a cheap $100 Crosman quieter yet with more power so this $200 Stoeger was a waste of money. The Stoeger scope was useless as well, but that's a different story. I also used a variety of pellets to see if length made a difference with weight, it didn't really. The power of heavies didn’t drop off as much as usual, but otherwise it was as expected.

Glad you don't trust advertised specs, but you also have to consider dieseling when a mfg or whoever tests them. I've seen many claims that were suspect, some probably exaggerations, and some unrealistic like a Trail shooting 14.3gr over 1000fps. I told the Trial guy it was probably dieseling and he replied it later settled to below 750. I've also seen crony results that showed high #'s at first, then settled, but were included in the avg. I also don't trust Cronys 100%, I had one give wrong #'s, and one person I'm helping right now with tuning is getting about 150fps low with his gun. I suspected he screwed up the tune but he discovered all his guns are 150 lower than expected. This is one reason why I have two Cronys.

The X20S is known to diesel for a very long time, people complain up to 200 shots. Mine had a ton of grease in it which explains why. I wonder if the mfg did this to bump velocity tests that might be done on it? Testers won't shoot a gun 100 or more times before testing so this would give it a velocity advantage. Obviously if Stoeger said it was an 850fps/11ftlb gun sales would drop, but they claim the same 1200/1000 as Crosman guns with full length barrels. Now the .22 X20S makes more power which two people have checked for me. Not ideal tests, but anything above 13ftlbs is saying something. I forget the exact numbers but one was 14 something and the other 15 something which is quite a jump. The more powerful one was tuned but I can't speak for the quality of the guys work. One guy kept the gun, the other considered it unacceptable and got a Benj Trail instead, which is also quieter and better in most every way so it's a win win. Imo the X20S is a hard flop, which I imagine is why they're dropping prices and will probably stop making them if they haven't already.
So, that's how this testing thing started with me, but with more than a few people "insisting" the old 6" rule still applies, and ignoring what I discovered as if it was a lie, it looks like I'll cut my next barrel to 6 as mentioned. That'll be fun to cock...
Btw, if shorter barrels were as good or better, wouldn't it make this suppressor craze so much easier? They could have 10" of suppressor to virtually silence the muzzle blast. Of course the X20S is my example of why that doesn't work, as is all the other mfg's sticking to long barrels and using stubby less effective suppressors.
Does this make it more understandable?

 

[JohnKSa]

...more than a few people "insisting" the old 6" rule still applies...

To be fair, the Cardews did qualify their test results by saying that a powerful sporter might benefit from a longer barrel.

I'll cut my next barrel to 6 as mentioned. That'll be fun to cock...

You can make a cocking aid by finding a section of steel pipe with an inside diameter that is similar to the outside diameter of the barrel. Slide it over the end of the barrel and the extra length will give you much better leverage.

They could have 10" of suppressor to virtually silence the muzzle blast.

Because of the way springers work, there's not a lot of air volume coming out the muzzle following the pellet. In addition, there is a fair amount of mechanical noise produced by the discharge. Silencing a springer doesn't usually give you more than about a 30% overall noise reduction, even if you completely eliminate the muzzle blast.

But you are correct, the short barrels do allow more effective use of suppressors. The TX200 and TX200HC both use that basic concept--that's part of why the apparent barrel lengths of both are about 4" longer than the rifled length.

Does this make it more understandable?

Yes. Do you still have the chrono data from the barrel length testing you did?

It would be interesting to see.

I'm also curious about whether there's a significant difference in the acceleration curve of a pellet out of a gas piston gun as opposed to a springer. I suspect that there's less piston rebound in a gas piston gun and that might help the pressure peak stretch out a little instead of dropping so abruptly.

 

[ChaoSS]

. In addition, there is a fair amount of mechanical noise produced by the discharge. Silencing a springer doesn't usually give you more than about a 30% overall noise reduction, even if you completely eliminate the muzzle blast.

So, in your opinion, how would one go about silencing a springer? A stock made of a different material to dampen some of the mechanical noise? I'd imagine the silencer would still dampen some mechanical noise, since the mechanical noise still comes out, partially, through the muzzle?

 

[JohnKSa]

I actually wouldn't recommend any of that unless you just see tinkering with the gun as a hobby in itself. If you actually want good results, the best approach is probably go with one of the better quality integrally supressed PCP airguns on the market.

 

[ChaoSS]

I actually wouldn't recommend any of that unless you just see tinkering with the gun as a hobby in itself. If you actually want good results, the best approach is probably go with one of the better quality integrally supressed PCP airguns on the market.

I intend to, one of these days, I was just thinking about quieting the springer for now. Just thinking that if most of the noise is mechanical, there really ought to be a way to quiet it a little bit.

 

[Chevota]

I’m sure I have the velocity data somewhere, but for now just a summary in a file for reference.

Chaoss: The quietest factory springer I’ve shot would be a Benj Trail AW in .22 with a heavy pellet. I say the AW because the heavy rubbery stock helps dampen sound too. A tune/mods can reduce it a little further. You can’t really do much more than that unless maybe you sprayed the gun with a thick layer of plasti-dip or something ridiculous like that.
A generic coil spring gun like a Crosman Quest which is almost identical except for the spring and barrel shroud is much louder. I can’t say by how much, but a Trail is day and night quieter. Most is due to the quiet nitro spring, then the majority of the rest is the suppressor. This is as perceived from the shooters perspective or someone next to them. From the targets perspective the suppressor makes a bigger difference.
A coil spring gun like a Quest can be made to shoot as quiet and smooth as a nitro with a little work, then by adding an inexpensive barrel from a Trail you have an equally quiet coil spring gun which is rare.
If you want to quiet one I can explain in more detail if needed.