How much does .40 factory gain in a carbine barrel?

[Surplussoldier]

If you are firing FMJ factory .40 caliber out of a carbine barrel (10-18"), will it gain in velocity? If you are firing 9mm and .40 factory ammo out of the same length carbine barrel, which will have more KE?

 

[R.W.Dale]

If 40 is faster than 9mm in a handgun it'll also be faster in a carbine. I have no expertice with .40 carbines but with a 9mm I would usually see a 150 to 200 FPS gain in a 16" barrel.

I would expect 40 in a rifle to practically be the equal to a 10mm in a handgun. I actually think it would make a nifty short range whitetail cartrige.

 

[JA]

I have never shot any 40 carbines but I have chronographed 9mm and 45acp pistols/carbines. Both resulted in 150fps or less increase in velocity with factory loads in the carbines due to the fast burning rate powders used in factory ammo. Using the slowest medium buring rate powders I could find to make reloads resulted in a velocity increase of a maximum of 230fps. The limited case capasity and pressure limits of cartridges designed for semi auto pistols precludes the use of the slowest burning rate handgun powders that really show large increases in velocity in the longer barrels of carbines.
Handloading 357 magnum cartridges really showed some amazing results due to being able to use the slowest burning rate handgun powders in the large volume of the 357 magnum cases. Depending on bullet weight the results were 400fps-800fps increases in velocity in a 18" barreled carbine versus a 6" barreled pistol.