Barrel Length question for AR-15 Pistol caliber uppers

[Greywolf]

I have the SBR forms approved, and am now ready to get the 9mm AR upp and .45 AR Upper cut down for eventual suppressors.

9mm - what barrel length? I was thinking of 8"-10" - have read a lot, but no one seems to have THE answer - will be shooting 147 grain subsonic almost exclusively through a suppressor.

45 - Looks like 7"-9" again may be the best bet. Again, will use subsonic (duh) and mostly through a suppressor.



Any ideas, guys? I want to optimize my accuracy and fps, but given my subsonic parameters and suppressor use I want the barrel as short as reasonably possible to get the ballistics performance I want.

 

[DMK]

So basically you want to know the barrel length for best velocity before the powder burns up and friction starts slowing the bullet down again?

 

[Greywolf]

Yes - exactly!

 

[happy old sailor]

reading in a book about gun laws it said making a rifle from a pistol was ok, but making a pistol from a rifle or shotgun was a no-no. just what i read, i did not read this in a BATF publication. you might look into it for being sure.

 

[kfranz]

He's making short barrelled rifles, not pistols.

 

[Greywolf]

Nothing wrong with taking an AR-15 lower that is properly registered as an SBR and putting a pistol caliber upper on it and chopping the barrel down. It is done all the time.