[345 DeSoto]

If a .45 ACP round chronographs at 850 (+/-) fps out of a 5" barrel, aproximatly what fps would the same round chronograph out of an 18" barrel...

[ForneyRider]

30-50fps per inch is a fair guess.

[351 WINCHESTER]

Depending on the powder and bullet weight it's in the vicinity of 1,000fps. The 9mm does better.

[rcmodel]

Not as much as you'd think.

The small powder charge runs out of steam & bore friction starts to take over in an 18" barrel.

I have a test of a Marlin Camp Carbine with a 16 1/4" barrel.

Win 185 Silver-Tip clocked 1,145.
Fed 230 Hydrashok clocked 1,071.
230 FMJ clocked 931.

From a 5" 1911:
Win ST 982.
Fed HS = 939.
230 FMJ = 849.

SO,
Win ST gained 163 FPS
Fed 230 HS gained 132 FPS
230 FMJ gaind only 82 FPS

That's a only little over 11 FPS / per inch average between 5" and 16 1/4"!

rcmodel

[jfh]

Below the nominal 5" barrel length is where velocity changes for a given barrel length get interesting.

For example, Power Pistol in a 38 Special +P / 140 gr. LTC load picks up about 80+ fps from a 2" to a 3" length, and another 70 fps or so from 3" to 4".

AA#5 picks up about 50 to 60 from 2" to 3" in the same nominal spec.

Jim H.

[taliv]

http://www.thehighroad.org/showthread.php?t=215654