barrel length and muzzle velocity question


max popenker
October 4, 2004, 02:10 AM

Does anybody knows how barrel length change affects the muzzle velocity for any given round in handguns?

I mean, if we'll shorten 5" barrel of a 1911 to 4", how much of MV we will loose with the same standard ball ammo?
Or, if we will increase the 4 1/2" bbl of some standard 9mm auto to say 5 or 6 inches, how much the gain in MV will be?


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October 4, 2004, 06:16 AM
There are the rules of thumb that indicate about 30 fps per inch of barrel, but it really depends upon the burning rate of the powder. Fast burning powders in a given caliber may be completely combusted within the first 3 or 4 inches of barrel, while slow burning powders may need 6 or 8 inches for complete combustion. So I can't say there is a hard and fast rule about this.

October 4, 2004, 10:45 PM
As stans said...there are a lot of variables that you have to factor in.

I've got some information on some chronograph testing that I did a while back with 9mm.

Remington 100rd Box of 115gr 9mm JHP. Gun used was a Kahr T9. 4.0" Barrel.

1. 1154
2. 1149
3. 1134
4. 1138
5. 1158

Average=1146.6 FPS

Now the figures from a 14.5" barrel 9mm AR15 . Remington 115gr JHP, 100rd bulk pack.

1. 1312
2. 1297
3. 1294
4. 1307
5. 1317

Average= 1305 FPS

This is an example of a fast burning powder and the relatively low velocity gains for the extra 10.5" of barrel.

In my limited chrongraph testing with a 3.0" 9mm PM9 vs a 14.5" 9mm AR I didn't find a lot of velocity gain as well.

Speer 124gr +P Gold Dots= 1093 fps vs 1374 fps.
Win USA 115gr JHP= 989 fps vs 1212 fps
Win USA 147gr JHP= 863 fps vs 1002 fps
Fed PD 135gr JHP= 926 fps vs 1133 fps

Hope this helps.
Good Shooting

max popenker
October 5, 2004, 02:19 AM
Red, thanks

But i more interested in gain in velocity by minor barrel enlargement, i.e. from 4" to 5" or 6".

Actually, i found one some very old and ugly design of pistol, in which the OAL of the gun is only 1 1/2 inch longer than barrel length. And i wonder if all the troubles of designer are worth the resulting gain in the MV and ME

October 5, 2004, 10:25 AM
Depends on the caliber. I tested some .38 Specials once in 4 inch and 2 inch revolvers and found standard loads lost 25-30 FPS while the hot, high performance loads lost more, like 80 FPS. Still not a huge drop.

October 6, 2004, 02:00 AM
Also, autopistol cartridges generally are shorter and have limited powder capacity, having been created after the use of smokeless powder.

Revolver cartridges often were developed before smokeless and were higher volume. There was a tendency to stretch the case to prevent higher pressure rounds from fitting in an older shorter weaker revolver. Now add in the magnums.

Generally, the auto pistol cartridges burn out quicker, givng only a couple hundred feet per second more velocity out of a carbine barrell.

In contrast, look how the 357 and 44 mags show a 400 to 600 FPS gain when fired from a carbine.

October 6, 2004, 02:53 PM
I think I understand what you are asking. The relationship between muzzle velocity and barrel length seems to be a curve. As the barrel is lengthened the muzzle velocity increases, but the gain in velocity slowly decreases. It is not a constant. Does that help?

max popenker
October 7, 2004, 01:52 AM
NMshooter, that will help if i will know the shape of the curve for any round like 9x19 or .45...

actually i'm lloking for cronograph data for some loads tested in pistols with different barrel lenghts, i.e. from 3.5", 4" and 5"... just to see how much difference is.

Island Beretta
October 7, 2004, 11:35 AM
I don't know if this helps but we once calibrated some steel plates on racks set at 10yds. for a match using my 9mm Beretta compact (4.3 inch). The calibration was tight as we wanted center hits and not peripheral hits to topple the plates. Surprisingly guys shooting it with Glock 19s and Walther P99s (4 inch barrels) even with center strikes could not topple it. We had to recalibrate using the Glock 19. I don't know how much of a difference there is in velocity but in hindsight I could have calc. the energy needed to topple the plates based on their mass.

By the way, the guys who used .40 S&W and .38 Supers sent the plates flying when they hit it even those with the compact Beretta 9000s (3.4 inch barrels). None of the 9mms did that, not even the big Beretta with the 5 inch barrel.

This was all very surprising to us as looking at textbook chrono figures we never knew that there would be such a significant difference in force between what we call minor barrel length differences in the same caliber and even in different calibers.

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