It prolly uses a rifle length tube. There are 3 main gas tube lengths: rifle mid and carbine. Best thing is to get a new bolt with a new barrel. The old bolt carrier will work.
"Gun control: The theory that a woman found dead in an alley, raped and strangled with her panty hose, is somehow morally superior to a woman explaining to police how her attacker got that fatal bullet wound." — L. Neil Smith
The problem with being stupid is you cannot simply decide to stop doing dumb things...
"I crapped my pants to avoid the draft!!" -Ted Nugent