Optimum barrel length for Pistol caliber carbine

[Onslaught]

I've got a little $$$ that I want to spend on a 9mm carbine. It will either be an upper for my pre-ban AR15, or a friend's pre-ban Feather AT9.

I've read many times that you don't gain much from a 9mm in a 16" barrel when compared to a 4" or 5" barrel because after all the powder is burned, the extra length of the barrel slows the bullet back down.

So at what length is the powder fully burned? It's still going at 5", judging from the fireball coming out of my wife's PT99. Would a 10" or 11" barrel have higher velocities than a 16" barrel? Most of the MP5's and other full auto carbines seem to have 10.5" barrels, so maybe they know something?

I know that 16" is the legal minimum, but since both options are pre-ban, I could always have a LOONG flash supressor permanently installed to make it legal.

Anybody do any actual testing or have some credible data on the subject?

Thanks!

 

[Chainsaw]

Hey Buddy, I did some testing
Ammo S&B 115fmj
Kel-Tec P-11........................... 1068 fps
S&W 5904...............................1175 fps
16" Marlin Camp Carbine........1283fps

About the same with my reloads as well.

I suppose one could work up a load for the carbine only making adjustments to soup it up. I would suspect one would have to check for strength of the action to make sure you could do this.

 

[Art Eatman]

Generalizing, 16" and longer barrels benefit cartridges like .44 Mag or .45 Colt more than the small-case cartridges like the 9mm.

Given the small capacity of a 9mm case, the gas pressure curve is falling quite rapidly by 12 to 16 inches of barrel, and there is little if any further gain. There is a gain over the common 4" or 5" pistol barrel...

Stuff like the MP-5: Those are really machine pistols, and short barrels not only provide adequate velocity but are much easier for rapid maneuvering in CQB.

I dunno. Seems to me that the camp-carbine type of gun is fun, and there's nothing wrong with that, but the utility is rather limited. Same for pistol-cartridge CAS rifles/carbines. Fun; adequate for close-range self-defense, but that's the general limit for utility. Again, purely IMO, but these sorts of guns are adjuncts to one's collection of "workin' guns".

Art