OK the question for today is...
How does barrell lenght effect velocity in 9MM?  If a round is loaded to sub-sonic speeds for a pistol with a 4" barrel, will it stay there when shot out of a 16" carbine barrel?  How about a 22" barrel? Or will it gain velocity, given the longer time that the gas is acting upon it?

One last.  Has anyone crono'ed this and come up with a good load?  (I know this part belongs in the reloading forum but i kind of blended the topics together.)

Generally, you will gain about 125-200fps with various 9mm loads in longer barrels. Anything over 10-12in. is not going to add much, even to +P+ loads and while I have never tried it, I would not be surprised if a 22in. barrel did not actually see a small velocity loss, especially with heavy bullets. IIRC, the Uzi / MP5 / Colt SMG's with nominal 10in or so barrel lengths usually can add about 150-175fps to standard 124gr. loads...meaning around 1300-1350 fps from NATO ball. (Been a long time since I chronographed any, though)

I've heard that the powder is pretty much burned up in the first 6-10" of barrel. I think a 16" barrel is a flash supressor in itself, but sshhhhh....dont tell the JBT's BATF!




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