i have an Aero upper and a Colt 11.5 that I am putting together that is sloppy as hell. it will fall right in and out of the upper. there is no tension holding the barrel extension to the upper so i was wondering what there is to use to bed the barrel to the upper other than loctite? I think i saw a guy on youtube use some brown substance in a brown squeez tube but that was a while ago and i can't find it now. What have you guys used and have you seen success?
also, since this is a short barrel im not worried too much about super duper precision but would like to see decent groupings... it is a colt barrel!!!

as always, i appreciate your guys opinions and info!

Darrin