I have a 4" and 6" Highway Patrolman and I was wondering how much of a gain in velocity is obtained when shooting the same ammo in a 6" barrel over a 4" barrel? I don't have the equipment to do such a test and I'm sure others have already done it. I don't have any idea of the velocity increase and would like to know. TIA.

__________________
Bill

Someone already has, indeed.

BBTI - Ballistics by the Inch :: .357 Mag Results

__________________
Alan
SWCA LM 2023, SWHF 220

The old rule of thumb was 50 FPS per inch, but it really varies with different guns and of course different loads in the same gun.

Nothing firm on this, but about 25-35 fps per inch for rifle or handgun, and that's very general based on many years of chronographing. There are too many changeable factors at play to give anything better than a loose "average". Another good reason to chronograph loads.

A 4" gun with a .004 gap and and real smooth rifling may well get better velocity than a 6: with a larger gap and somewhat rougher rifling. One barrel is .3575 and the other is exactly .357. One load uses fast burning Bullseye and the other slow burning 2400 and there will be a bit less difference.

But, here is what I feel about that. The sighting radius will have more effect than the velocity. The effect on anything struck with a bullet going 100fps slower will be minimum and and anything poorly struck by either won't show much difference either. Your bullet being just 1" closer to fatal areas will have more effect.

That said I would rather be up against against a mediocre shot with a 6" gun than a good one with a 3" at 25 yards or more.

Which brings up another point. The ballistics of a handgun bullet. The drop from a bullet going 100fps less at 100 yards is negligible when compared to group size 99% can achieve at that range. At closer ranges the trajectory differences are even negligeble

I used to be a big fan of 6" guns and once built a Super Blackhawk 44 mag with a 14" barrel. Now, I mostly like to carry guns 4" or under. Walking around a 6" is ok on your hip, but sitting down, driving etc it is more problematic. Not terrible, just not as easy for what I think you gain.

On the average, you should see a increase of 50-60fps per inch in handgun barrels of 2-8 inches. The increase in velocity starts to fall off with longer barrels.

But this is just an average and your M28’s could be the exception to the rule. For example, I have a 6” model 66-1 that consistently outperforms my 8 3/8” model 27-2 by a bit over 50 feet per second using the same box of 158gr ammo despite having a shorter barrel. Only a chronograph can tell you for sure how your guns are working.

Years ago I tested several brands of 22 ammo in guns ranging from 2" to 29" barrel length. I was surprised at the results. I often hear a 22 peaks at around 16" but that was not my finding. Speed kept increasing with barrel length up to 25" or more. Now, the gains after 20" got pretty small but there were gains. Of course I was using different guns and not cutting down the barrel on the same gun so not a perfect test.

I did compare velocities of 38 Special ammo in 2" and 4" revolvers. My carry load clocked 1150 in a 4" gun and around 1100 in a 2" barrel. Should have tried a 6" gun for comparison.

__________________
No life story has happy end.

Having worked chrono on a lot of matches, IMHO guesstimates of what a given gun will chrono aren't worth spit. I have two "identical" Model 66s that consistently chrono 30fps different with PF 133 USPSA loads.
If you want to know, chrono.

__________________
Science plus Art

M-28 4 inch 145 grain Silvertip (1290 fps)
1129 fps avg
M-28 6 inch
1412 fps avg

M-28 4 inch Remington 158 soft point (1240 fps)
1178 fps avg
M-28 6 inch
1301 fps avg

your results will probably vary

Curious as to why the 4" gun is so much slower. Would expect some but 223 fps and 283fps seems like a bunch.

Just out of curiosity do you know the B/C gap on those 2 guns.

no idea on the cylinder gap as it may or not make much of a difference in the long run.

there is such a things as guns that are "fast" and some are "slow".

I had a Ruger #1A with a 22 inch barrel and a #1B with a 26 inch barrel in 270 Winchester. the #1A with the shorter barrel was within 30 fps of the 26 inch barrel.

every gun is different. I have chrongraphed several hundred loads of various caliber over an Oehler 33 chronograph and you learn something every time out.

different lots of ammo could be and will probably be different

Oh ya, things like actual chamber diamentions, barrel smoothness, and exact size of the bore and rifling can have effects. Just that the B/C gap is variable many point at. It does make me curious.

Thanks for all of the great input. Factors involved I hadn't even considered! I had no idea of the actual velocity but as stated in will be in the 25-50 fps per inch range.

__________________
Bill

The round that surprised me over my chrono was a 460 200gr Hornady!
8 3/8" S&W revolver was 2452fps and my 20" TC was 2999fps! The TC is much more pleasant to shoot!
jcelect

I agree 100%, and that is why I chronograph every time I load with new bullets.

The round that surprised me over my chrono was a 460 200gr Hornady!
8 3/8" S&W revolver was 2452fps and my 20" TC was 2999fps! The TC is much more pleasant to shoot!
jcelect

what is factory velocity for this load? that almost looks like you had the muzzle too close to the first screen

4” is too short for magnum, 6” is to long to holster in car or on horse, that is why 5” is best length for magnums!

__________________
V/r,
Markham

+1 , the rule of the thumb for 1000fps muzzle velocity on wards the variation is +-50fps for changes in barrel lenghts of +- 1",..
Regards
RR

__________________
"Off we go..."

6”/6.5”/7.5” shoulder holstered.? You can’t tell I got it on. Even in a car. I have a shoulder holster for a 10.5” barrel.

Your talking different FPS what about accuracy between the shorter vs longer barrels?

__________________
Plant garlic in the fall

Here is an answer to the OPs!
BBTI - Ballistics by the Inch :: .38 Special Results question
jcelect

For what it is worth, I have a 6 inch Model 29-2 I bought new in 1979. I also have a 4 inch 629-6 I bought new in 1995. The 4 inch gun averages 50 feet per second faster across the board with almost all loads I have chronographed in these two guns. I believe the newer gun has tighter dimensions than the old. I also believe that with 4 to 6 inch or so barrel lengths that other gun dimensions are more important than 2 inches of barrel length generally speaking.