Optimum Barrel Length for .45acp

[amprecon]

I've been looking at carbines in .45acp and got to wondering at what point does barrel length start to inhibit the velocity of the .45acp cartridge. I think the Tommy gun barrel length was 10.5" (?), was that the optimal length before barrel friction started to slow it down? The H&K UMP .45acp submachine gun barrel length is just under 8".
Since minimum barrel length for rifes/carbines is 16" without going through all that BATF crap, I'm not going to buy a .45acp carbine if 16" of barrel length starts to slow down the .45acp before it even leaves the barrel.
And no, I'm not interested in other calibers.

 

[Tape]

The longer the better "that's what she said" by Michael Scott.

The longer is better but not practical for a handgun.
For carbines perfect. Also, the longer the more the velocity without a slowdown, the barrel would have to be stupid long to when "slowdown" takes effect

 

[jon86]

Here's a good place to start.

http://www.ballisticsbytheinch.com/45auto.html

 

[Roughneck08]

But also remember that the .45 ACP was created around the 1911. Yes 9mm and 40 do good with barrel length and gain more velocity but aren't the same as 45. Wait till someone more inclined in this area chime in.

 

[Effigy]

Based on the above link, there seems to be little (~50 fps) gain in velocity from going from a 5" barrel to 18" barrel with standard pressure rounds. For high pressure loadings, there can be a significant increase. For instance, the Cor-Bon 165gr +P gains 212 fps in the 18" barrel versus the 5" barrel.

 

[TonyAngel]

I'm no ballistician, but I believe that the .45 is one of those rounds that does well in a short barrel. It is a low pressure round and is usually loaded with some pretty fast burning powder. Look at the numbers posted by Effigy. Even with the Cor-Bon, there is only a gain of roughly 20% velocity for an over 300% increase in barrel length. I'd say that for standard ammunition, 5" is probably ideal.

 

[merlinfire]

based on what BBTI is saying, for standard factory loads it tops out around 11 inches which would be a SBR, but if you're using the +P loads it tops out at 16" which would be ideal for a carbine.