Ballistics by the Inch

[3leggedturtle]

Don't know who posted about this, but I thank you for it. Lots of interesting info on it. Especialyl with 25, 32 and 380 ACP ballistics.

[Blaine]

Was there a link to go alone with this?

[FWiedner]

Maybe it's something cryptic like:

http://www.ballisticsbytheinch.com/

[Blaine]

Maybe it's something cryptic like:

http://www.ballisticsbytheinch.com/

Your abilities with the arcane are truly amazing....

[3leggedturtle]

Was there a link to go alone with this?

No don't have a window to surf my other site; while reading ballistics when I'm alone

I just type in Ballistics by the Inch. Guess I'm just simple minded and my laptop helps me thru it.

[Blaine]

(Reluctantly letting dog lick egg off my face)

[AJMD429]

Maybe it's something cryptic like:

http://www.ballisticsbytheinch.com/

Your abilities with the arcane are truly amazing....

I'll bet he has a job in IT somewhere. . . maybe we should get Hobie to make him FWiedner instead of just FWiedner...

[Blaine]

Maybe it's something cryptic like:

http://www.ballisticsbytheinch.com/

Your abilities with the arcane are truly amazing....

I'll bet he has a job in IT somewhere. . . maybe we should get Hobie to make him FWiedner instead of just FWiedner...

I second that motion....HMFIC of Tact and diplomacy....

[Ji in Hawaii]

I especially like the info on the 357 magnum supporting the fact that 16" is the optimum barrel length for this cartridge efficiency wise. You start losing energy when you go any longer.
I love my 94AE 357 mag Trapper!

[BAGTIC]

I suspect the 'optimum' length will vary according to the load and powder charge with heavier charges of slower burning powder topping out at longer lengths.

[Model 52B]

I especially like the info on the 357 magnum supporting the fact that 16" is the optimum barrel length for this cartridge efficiency wise. You start losing energy when you go any longer.
I love my 94AE 357 mag Trapper!

This chart is a great example of the many flaws in the "ballistics by the inch" approach.

If you look at 16" versus 17" velocities across the board, you see a drop in velocity in every single round tested. However when you compare the 17" and 18" numbers you again see an increase in velocity in all but one instance.

Now...you can look at the 16" and 17" numbers and conclude that bullets start slowing down after 16" and that 16" is the optimum length - but you'd be wrong. Sorry - that's just the statistical reality here.

First, the sample sizes they used in this experiment are small, and it makes it difficult to show that the changes in velocity are statistically significant. That's not the case at this point in the data - as this data is consistently wrong across the whole row, not just for one round, but it is evident at various points through out the various charts they use. If you saw the raw data, you'd see the effect a single fast or slow round has on the average they then use. They take some crude precautions against that in their test protocols, but it is not enough to make up for inadequate sample sizes. So when it fails to pass the smell test, you need to acknowledge the bogus data points.

Second, the regularity of the barrel is a confounding variable. Unless the barrel was air gauged and was known to be consistent through it's entire length you can't discount the possibility of looser or tighter sections of the bore and/or at the muzzle have an effect on increasing or deceasing velocity to a degree that exceeds the difference due simply to length. That's a real possibility in the kink in the trend line that occurs in the 16"-17"-18" data.

Third, cutting and re-crowning the barrel takes time and differences in ambient temperature has an impact on the measured velocity. If I shot the 17" numbers in the morning when it was cool, then cut and re-crowned the barrel and shot the 16" numbers in the afternoon when it was hot, then the increase in velocity due to differences in ambient temperature may well exceed decrease in velocity due to the shorter barrel.

Fourth, shooting a large number of rounds through the bore creates heat. If I used a greater rate of fire and warmer barrel temps at the 16" mark than I did at the 17" mark, then my higher velocities at 16" may be due to experimenter error in not maintaining consistent bore temps.

That may be unintentional if I assume it won't make a difference, if I was getting pressed for time, etc, or it may be a form of experimenter bias if I expect to see the "break" at this point and test accordingly.

Fifth, there are other potential confounding variables. For example it could simply be a very minor error in distance between muzzle and chronograph due to different placement of the chronograph or even placing the barrel and test fixture farther forward or aft on the bench.

All of that has to be considered to explain the discrepancy in the trend line from 18" to 17" to 16" in the data. All you can really conclude without having access to all the raw data, and some very detailed test conditions (consistency of the bore, sample size, ammunition lots, ambient temp, bore temp, time between shots, dwell time of the unfired round in the warm chamber, distance from muzzle to chronograph, etc) is that there was a flaw in the test protocols that produced a nonlinear result in the data.

-----

In my experience with .45 Colt, where the bore volume expansion ratio per inch is even higher than in .357 Mag, is that I get higher velocities with a 20" barrel than a 16" barrel, and I get higher velocities with a 24" barrel than I do with a 20" barrel. Plus, I get lower standard deviations with the longer barrels, suggesting better consistency in powder burn in the longer bore.

Don't get me wrong, I like a short handy barrel as much as the next guy but I never kid myself by thinking the shorter barrel is faster even in a pistol caliber - I've chonoed thousands and thousands of rounds in a number of calibers in a variety of rifles and I've never found that to be the case.

You will see definite points where the velocity gain per inch flattens out and additional inches may not be worth it in terms of the velocity gains - but the extra length never creates a net loss in velocity - and in most cases longer bores improve consistency as measured through a reduced standard deviation in measured velocity.

Realistically, you will not see a loss of pressure behind the bore sufficient to create "suction" (relative to the aerodynamic pressure in front of the bullet and the frictional drag from the bore on the bullet) that slows the bullet until you've got a barrel length measured in yards.

The only common exceptions here are with a) very light center fire loads, and b) the small gallery rounds in .22LR powered by the primer compound only, and then the issue is more often than not the choking that is often done in the end of the bore in a .22rimfire.

[KWK]

... differences in ambient temperature has an impact on the measured velocity...

Excellent points.

In my experience with .45 Colt, where the bore volume expansion ratio per inch is even higher than in .357 Mag

I don't follow this one, though. The case and cartridge lengths as well as the bullet SD's are nearly the same in both. The expansion ratio should, then, be nearly the same as well. Your results--that 20" is better than 16"--for a rifle makes sense to me.

[Mike Rintoul]

Using the BBTI data is a stuff shoot at best. Case example - I have a client that wanted more velocity from a 45 ACP with a 3 1/4" barrel. With client chosen 230 grain bullets, a change of powder and primer on my end with a certain crimp added nearly 45 fps. This was still short of the clients goal but nothing more I could do without exceeding safe parameters. The client had a custom barrel-maker address the issue. I was not sure how the process and technology would play out. A certain twist combined with particular and specific depth of grooves and shape of lands with the chosen bullet added another 22 fps average and put the ballistics where the clients wanted them so the bullets would consistently function as designed. A load change and a custom barrel achieved 67 fps more velocity over a factory load with the same bullet, with a minimal increase in pressure.

Second instance: Experimenting with some vintage .22 rimfire rifles, a 1950 Marlin with cut rifling pushed a CCI stinger 1690 fps average. Other rifles with different rifling and different barrel lengths from 16 1/2 inch to 26 inch did not achieve that much velocity, with the next highest coming in at 1621 fps average. Why/how does this specific rifle push the bullet to that speed is an unknown.

My point is that BBTI shows a specific load in their specific test barrels of various length. You can ballpark the same exact factory load but the science is flawed, as there are numerous other effects on velocity that cannot be accounted for in their charts.

[piller]

Mike, I would rather not change the barrel on a firearm just to get a few feet per second more velocity. In the relatively tiny amount of handloading I have done (compared with your knowledge, and the experience of many others here), I have just lucked into finding that one of my firearms likes the loads at maximum for best accuracy, and another likes the velocity to be on the low end of the scale. Each firearm is slightly different.

[Model 52B]

... differences in ambient temperature has an impact on the measured velocity...

Excellent points.

In my experience with .45 Colt, where the bore volume expansion ratio per inch is even higher than in .357 Mag

I don't follow this one, though. The case and cartridge lengths as well as the bullet SD's are nearly the same in both. The expansion ratio should, then, be nearly the same as well. Your results--that 20" is better than 16"--for a rifle makes sense to me.

In a .452 diameter bore, the volume will increase by .160 cubic inches for each inch of barrel length. In a ,357 bore you have only .100 cubic inches for inch of barrel, so for each additional inch of .452 barrel you are gaining a lot more volume.

Even assuming similar starting pressures (which is not accurate as the .357 operates at higher pressure than even a Ruger only .45 colt load - 35,000 psi versus 32,000 psi), the .357 is going to maintain more pressure in a barrel of any given length than the .45 Colt. The point being that if a .45 Colt is still gaining velocity from 16" to 20", the .357 will still be gaining velocity as well.

[Pete44ru]

.



Phew ! I'm perfectly happy that my head's where the Sun don't shine.............. .




.