Basic Velocity Question

[Ptarmigan]

Is there any accepted rule of thumb for what the average muzzle velocity drop is when going from a 4" revolver barrel to a 1 7/8"--2" snubby barrel?

We will assume barrel/cylinder gap is identical on both firearms, and the exact same cartridge is to be fired.

Simplest example: A 158gr LRN bullet achieves an average MV of 800 fps when fired from a Model 10 4" barrel. What would be the average MV of the same bullet when fired from a Model 36 snub nose?

 

[OKFC05]

First thing you learn when you buy a chronograph is that the rules of thumb are just guesses that have little to do with specific barrels and loads.
First, if you assume the published tables represent the velocity in your gun, that's a guess. If you then assume another gun with a shorter barrel will be X amount less, that's just another guess.

I have two identical 4" S&W revolvers that are consistently 30 fps different with my IDPA load.

I've measured loads from a specific 3" model 65 that were FASTER than the same load from a specific model 10 4".

Years ago, an article in the Rifleman used the same barrel and cut it successively shorter, measuring different loads. Then they tried to get a regression equation vs length (scientific rule of thumb) and found it depended greatly on the specific powder used how much velocity was lost with the shorter barrel. So they concluded a general rule of thumb varied so much with powder and load as to be unreliable.

 

[427mach1]

^^^ What he said. I have two .41 magnums, a Blackhawk with a 6-1/2" barrel and a Redhawk with 5-1/2" barrel. I have measured the barrel/cylinder gaps but don't recall what they are. Chronographing my hand loads through both guns, the Redhawk, with the shorter barrel, had higher velocities. The load is 21.2 grains of 'Lil Gun with a 265 grain Cast Performance LWFNGC. Blackhawk averaged 1334 fps while the Redhawk averaged 1406 fps.

 

[REM 3200]

Chack out this site:

BBTI - Ballistics by the Inch :: Home

 

[ArchAngelCD]

The only rule that holds true is there are no real rules when it comes to ammo velocities in different guns. Sorry, I know that's not what you wanted to hear but it's true. It can be anywhere from a 50 fps difference up to 200 fps or more...

 

[Steve C]

I have crono'd three 158gr .38 spl loads through 2 different 4" S&W's and a 2" Detective Special revolver on the same day. Velocity loss through the shorter barrel was at least 86 fps to a maximum of 119 fps less average velocity. This was for 3 powders, 2 loads using Unique, and one each using Tight Group and W231. There is enough differences between guns with the same barrel length to make precise estimates impossible but a loss of 100 fps going to a snubbie froma 4" service revolver is likelly to be fairly accurate with 158gr loads.

 

[alwslate]

In my experience with handloads using 158 gr cast bullets over small
charges of fast burning powders in S&W revolvers, a realistic loss of
around 75 fps would be seen. Results can vary quite a bit when old vs
new guns or guns of different makes are compared. BC gap can be a
significant issue as well and I would pass on almost any used S&W
with a too large BC gap even if I wanted that model.

 

[Titegroups]

When you get a rough guess together plug those numbers into an energy calculator, energy is calculated by weight multiplied by the velocity squared, so a small reduction in velocity really effects the energy output.

 

[s&wchad]

It doesn't answer your question, but you might find this interesting. Scroll half way down in the post. http://smith-wessonforum.com/s-w-re...85299-500-magnum-nuts-faqs.html#post135892869

 

[riverrat38]

Buffalo Bore lists "real gun" measurements for their ammo. For example, for their "FBI" load, non plus P, 158 gr HPSWC, part 20C, they list the following:

S&W M60 with 2 in barrel, speed is 854 FPS
Ruger SP 101 with 3 in barrel, speed is 930 FPS
S&W Mountain Gun with 4 in barrel, speed is 979 FPS.

This ammo is optimized for short barrels, and the guns are from different companies. As you go up in barrel length, the differences per inch get less. Ammo optimized for longer barrels would likely show more difference is speed per inch of length.

rat