I use green high temperature bering sleeve retaining loctite. The barrel extension is like a sleeve and not threaded ... and really strong and high temperature, like a hot AR barrel.
Do Not need heat for taking the barrel out of the upper receiver...Just use Johnson Paste wax on the area of the upper receiver and buff out leaving a slick polished ares where the barrel extension fits into the reciever bore...now lightly dab the green high temperature bering sleeve retaining adhesive to the barrel extension...and assemble and tork to 60 ft/lbs. Use a quality barrel only one of 3 BA barrels were of spoty acceptable accuracy...even the 1" moa guarantee...yeah sometimes 3 shots will achieve 1" but never 5 shots....mostly 1.5" to 2.5 " 5 shot groups.
To remove glue in barrel with waxed reciever is simple: Use a 30 mm oak AR 10 or (1" oak on AR 15) cut down to barrel extension dia. for 1.5" in length . No heat just insert your special 30 mm Oak dowel about 2.5 feet long into the reciever. Hang on to the barrel with the nut removed of course and bang on the concrete floor, soon the barrel will begin to separate from the glued receiver...all the glue on the barrel none in the waxed reciever.
There are other things I do that require lathe and milling machine, to enhance accuracy in an AR. Squaring the reciever, centering the bolt carrier, glue in, high end barrel...and always the same torque, I mill a groove for the gas tube if it doesn't line up, at 60 ft/lbs . Except for 9 mm blow back...all buffers and springs are mill spec. So all lowers are inter changeable AR 15 for all AR 15 calibers, and AR 10 lowers are interchangeable with uppers ...they all have the same buffer and springs. The barrel gas system sets up the AR function for individual calibers, with adjustable gas blocks if necessary and /or drilled out gas ports.
The buffer and its spring has slight tension on the bolt carrier as the AR is hinged together and the take down pin pushed in. I do not mess with that. It should go together easily with the buffer being pushed back slightly into the buffer tube, when the firearm is closed..machine a slightly larger chamber on the front of tbe buffer helps close it if it hangs up a bit.
An AR will shoot 5 shots under .5" when assembled correctly with a good barrel, even in the .2" .3" and .4" area but .4" to .6" very common. Or 12 shots into .59"
But not everyone has the tools to do everything, much can be accomplished, starting with a premium barrel, aftermarket trigger, good scope, & good handloading practices...costs money and time, few short cuts, and all learned over time.
