07-15-2020, 02:53 AM
Criterion uses Loctite 609 for their assemblies. it takes the least amount of heat (300F if i recall correctly, but if i were you i'd double check) of their sleeve assembly compounds to disassemble. i think 620 takes like 450F to loosen. others measure OD of the barrel extension and ID of the upper tunnel and wrap in a shim in of the correct size to take up the gap. if i recall the BCM upper has a slighty undersize extension tunnel on their upper and you have to heat the upper extension tube area to get a barrel slid in. it's an interference fit. check for previous reply links in the forum on upper barrel bedding. there are a lot of them.
-tdbru
-tdbru