Accuracy of Manufacturers Ballistic Data

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jjjjeremy

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Has anyone here chrono'd stock ammo and compared it to the FPS that the manufacturers claim? I don't have access to a chronograph, but I'm interested in buying an XR turret for my Nikon scope and I'd like to know what the general margin of error for the manufacturers' claims.

Thanks!
 
even if you tested a group of benchrest quality barrels from the same mfg, you would find some variation by individual barrels probably on a normal distribution. then there is much more variability based on how many grooves and their shape, how tight it is, how long it is, what chamber was used (e.g. tight neck or short throat or what)

from an ammo mfg perspective, they have no idea if you are going to shoot their stuff from a long 30" or short 16" barrel, one with a gas port or not, or if your barrel just happens to be fast or slow. best case, their number will tell you what length barrel they tested it from.

then the ammo itself will have some variation based on whether it's match ammo with a consistent powder drop and consistent neck tension, or if it's hunting ammo that they just threw together and crimped, etc.

beyond that, it's just a guess. if you asked specifically about which ammo and which gun, there might be some members here who could give you a data point or two
 
Numbers can be all over the place, depending on wear, rifling twist, tolerance stacking, temperature, throat dimensions, etc. Manufacturers use SAAMI standard pressure barrels that are sized to minimum dimensions to produce highest pressures which they then measure to verify they're within safe limits. YOUR firearm probably isn't bored/chambered/throated as tight, so you probably won't get catalog velocity.

And if your barrel is shorter than what the factory used, well, that's another potential source of velocity loss.

I've found that my rifles will typically lose 100-200 FPS (sometimes more) over factory claimed velocity, using barrels of the same length. And this varies by ammo manufacturer. Other shooters I've spoken to have generally found the same.
 
At best the data is an approximation. When I was a sniper instructor, we chrono'd match grade ammunition, from the same box, through the same chronograph, using several M24 sniper rifles- which are very high Q-C rifles built by the Remington custom shop for the Army, (guaranteed 1 MOA, but mine fires closer to 1/2 MOA) and they had different MV's by as much as 48 fps from different rifles, but got consistent results from individual rifles shot-to-shot (indicating the chrono was working properly). Also, the MV from a 308 Ruger American predator (18" 1:10 RH 6 groove) is going to differ significantly from a M24 (24" 1:11.25 RH 5 groove) for example. In most if not all cases, ammunition manufacturers don't provide data such as the specs or make/model of the rifle used when they tested the ammunition. Even if they did, and I had an identical rifle, I still wouldn't believe it until I tested the ammo- if for no other reason, based upon my experience described above.
 
Thanks for all the info!

To give you guys some more details, this is in a Win 70 .270 with a 24" barrel, shooting Barnes VOR-TX (TTSX monolithic copper, 3060fps), Hornady Superformance (GMX monolithic copper alloy, 3190fps) and Hornady Full Boar (GMX, 3050fps) with 130gr in each.
 
I can assure you that it got that speed in the barrel they tested it in. But the speed from your barrel could be slower by more than 100 fps. Or it could be right on the money. There really is that much difference in individual barrels.

Custom or higher quality barrels manufactured to closer tolerances tend to shoot faster. Most of the ammo makers test their ammo in high quality barrels and most common factory barrels are usually somewhat slower. The few times I've chronographed factory ammo it has been a little slower, but within 20-30 fps most of the time.
 
You've gotten good information here. In general, the manufacturer number are accurate, but because speed and energy sells they do a lot to ensure the number is as high as possible. Usually their test barrel is longer than typical for caliber, and the chamber is minimum spec (also required for pressure testing) and as a result the numbers are higher than what you'll actually get.

Personally I would chrono before buying a ballistic turret, or if that's not possible for some reason I'd subtract 100 ft/s from the box value as a guess.

Bullet manufacturers BCs also tend to be measured at higher velocities than you'll actually achieve, which also makes loads shoot low relative to ballistic turrets. I'd probably take a couple 1/100s off the supplied G1 BC if there isn't a Brian Litz number you can trust.
 
I have tried some different brands. Some are very close and some is over and some is way under it is also what the weather is hot cold. It has been years so know they do have new powders that is not affected by the weather as bad.
 
Bullet manufacturers BCs also tend to be measured at higher velocities than you'll actually achieve, which also makes loads shoot low relative to ballistic turrets. I'd probably take a couple 1/100s off the supplied G1 BC if there isn't a Brian Litz number you can trust.

Good point, but note that Sierra provides G1 BC numbers over various speed ranges in their published detailed bullet chart. This helps you figure out a realistic BC for your speed range. Some of the bullets have widely changing BCs by speed and others change by tiny amounts.

Berger and Sierra offer accurate ballistic data on their bullets. With all other brands that I know of I would agree with the quote.
 
JJ, Looking at the info you provided I would expct your MV to be very similar to the stated MV on the ammo you are using. Companies like Hornaday,Winchester and Remington do a good job of not overstating their MV to much. That being said, if you were shooting a 16 inch barreled AR with ammo rated at 3240fps there's a good chance your measured velocity would be closer to 1800-1850 fps at the muzzle. I have a Nikon Custom Turret and love the longrange accuray it goves me.
 
soooooo, I broke down and picked up a Caldwell chronograph. I'll post up a list of my results. I found one range near me that rents chronographs, but at $15 per use, a $70 tool seems worth it.
 
Good point, but note that Sierra provides G1 BC numbers over various speed ranges in their published detailed bullet chart. This helps you figure out a realistic BC for your speed range. Some of the bullets have widely changing BCs by speed and others change by tiny amounts.

Berger and Sierra offer accurate ballistic data on their bullets. With all other brands that I know of I would agree with the quote.

Good point. Berger you can trust their G7 number. Sierra gives G1, but they give them at several speeds so you can get an idea of what's what. Of course you need to make sure your turret makers takes all this into account, or you'll get a sketchy turret.
 
Don't forget that velocity data is obtained from test barrels set in universal receivers that don't move under recoil. You will get faster MV numbers from that set up compared to being shot from the same barrel in an arrangement that allows the barrel to move rearward.

For the record, I get 50 fps faster average MV shooting Hornady 6.5 CM 140gr Match ammunition from my AI with a 24" barrel compared to the 2,700 fps on the box.
 
Has anyone here chrono'd stock ammo and compared it to the FPS that the manufacturers claim?
Yes, have done it many times with .22LR, .38 Special, 9mm, 45acp, 38 Super, .243, 308, .30-06, etc., and found that MODERN factory ammo velocity specs are pretty close. Not so for the vintage stuff, whose performance was often overstated.

Industry standards for handgun ammo were changed in the late 1970's, and you no longer see those unreasonable numbers advertised. This is what makes some folks think factory ammo has been reduced in power over the years, but in reality those .38 Specials are no longer being quoted out of 10" unvented barrels. Plus, now days anybody that wants to can have a chrono for themselves, so the factory cannot claim as much misleading info as in the past.
 
Of course you need to make sure your turret makers takes all this into account, or you'll get a sketchy turret.

Additional tip to OP: if you're going to rely on a ballistic turret or reticle, it's a good idea to zero at the longest distance you're likely to shoot, using the turret or reticle mark for that distance, then work backwards and find what your impacts are at shorter distances. This is much more likely to get you on target at the farther distances. You will probably find some difference between the aiming point mark and the impact at shorter distances, but 3" off at 200 or 1" off at 100 is insignificant compared to maybe 24" off at 500.

Another option is to chrono your intended load in your rifle and use that velocity plus the bullet information to generate a ballistic chart providing either mil or MOA adjustments required at various distances. This may sound like more work, but isn't much compared to doing things right with a ballistic reticle or turret, and lets you use one scope for a wide range of bullets just by checking muzzle velocity and doing a new calculation. There are several free online ballistic calculators that will do the calculations for you.
 
Additional tip to OP: if you're going to rely on a ballistic turret or reticle, it's a good idea to zero at the longest distance you're likely to shoot, using the turret or reticle mark for that distance, then work backwards and find what your impacts are at shorter distances. This is much more likely to get you on target at the farther distances. You will probably find some difference between the aiming point mark and the impact at shorter distances, but 3" off at 200 or 1" off at 100 is insignificant compared to maybe 24" off at 500.

Another option is to chrono your intended load in your rifle and use that velocity plus the bullet information to generate a ballistic chart providing either mil or MOA adjustments required at various distances. This may sound like more work, but isn't much compared to doing things right with a ballistic reticle or turret, and lets you use one scope for a wide range of bullets just by checking muzzle velocity and doing a new calculation. There are several free online ballistic calculators that will do the calculations for you.


Thanks for the info! Good tip to verify and zero at the longest range expected.

I've already done a few ballistic cheat sheets for MOA, graphing out range/MOA on an xy axis. To be honest, it's a mixture of laziness and cool factor. I don't imagine changing loads often enough to make the turret an issue.
 
Not usually a rifle caliber but germane to manufacture’s data.
Winchester 30 Luger, 93 grain hardball. Winchester claims 1220 fps from a 4.5 inch barrel.
For some calibers SAAMI calls for a tight test barrel, for some calibers SAAMI calls for the same identical specs for test and production barrels. In the case of the 30 Luger SAAMI calls for the same barrel specs for both.
In a semi-auto pistol between 10 and 20 fps will be lost due to the recoil of the upper.
For pistol calibers such as this there is a significant gain in velocity with longer barrels.
Tested in 4 inch, 4.5 inch, 5 inch, and 6 inch barrels in two different makes of lugers and a Ruger P85. It’s worth noting that having measurements for more than 30 luger barrels in 30 caliber I found they have much tighter tolerances than you sometimes hear.
So what did the chrono reveal? I don’t have the actual numbers to hand but well recall the general results.
Average velocities ranged from around 1050 for the 4 inch to around 1175 for the 6 inch. No single round reached 1200 fps in the 6 inch.
In all cases, the load had barely enough steam to cycle the action.
I contacted Winchester about this but they gave me short shrift. I contacted Ruger and they gave me a couple of recoil springs to play with gratis. (The P85 in 30 Luger has a different spring and guide rod than the 9mm version.)
The original DWM specs called for 1220 fps from a 4.5 inch pistol, not a fixed test barrel. I have reason to believe this figure was spot on. And this was not muzzle velocity but average velocity over about 15 meters starting a meter from the muzzle. I went to the trouble of researching how they measured the velocity, and while what they were measuring was slightly different, the accuracy was quite good.
 
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