I was talking to a guy today about various pistol carbines. I said one in .40cal or .45acp would be awesome. He tells me that .40 and .45 are piss poor carbine calibers. He states they actually lose velocity in the longer barrel and that 9mm is better because it gains speed heading out the barrel, which is why 9mm is the preferred .mil caliber for their sub guns. Furthermore, a .45 round coming out of a tommy gun is actually slower than a 1911?

How much of this is true and if its false give me some links to lay the hurt...

18 hits and no response?

http://www.ballisticsbytheinch.com/



 

My personal experience indicates the exact opposite.  A .45 ACP will produce more velocity from a 16" carbine  barrel than from a 5" handgun barrel.

I do believe this rumor has some slight basis in fact however.  People who report low velocities are usually using Marlin Camp Carbines.  My Cav/Oly .45 has always produced higher velocity than any of my Gov't models.

So people who claim this might occasionally be correct, but they are not correct most of the time.

another thing to consider, if you reload, you could use a slower powder to
utilize the longer barrel length for more velocity.  I have lost the link
but I found a recipe for 9mm for the "uhg" high point carbine that we have, it looked
promising.

speed