04-23-2021, 10:55 PM
(This post was last modified: 04-23-2021, 10:59 PM by drewthebrave.)
I've used a handful of BCM uppers on builds, and it seems like every fitting is a little different. My LaRue PredatAR, Bergara SPR, and Alexander Arms barrels took a heat gun and a few light taps of a mallet to get set. A Wilson Combat SR barrel was juuust able to slide in without any thermal fitting needed at all, so I bedded with some Loc-tite to take up the very minimal slack. FWIW, that same WC barrel wiggled like crazy in a standard upper receiver.
The toughest assembly was an Anderson Mfg Grendel barrel that I couldn't get past 1/8" into the receiver with heat alone. So I put the barrel in the freezer overnight. I heated the receiver over my stove (right next to the fridge) to get everything together while the temp differential was most extreme. It got the barrel about 75% of the way in to the receiver before it got stuck. Each part was literally just seconds away from their heat/cold source when it stopped moving. I hammered it the rest of the way with a mallet before the fit had time to get much tighter. Despite the tight fit, that particular barrel wasn't a great shooter, whereas all the others were solid performers.
The toughest assembly was an Anderson Mfg Grendel barrel that I couldn't get past 1/8" into the receiver with heat alone. So I put the barrel in the freezer overnight. I heated the receiver over my stove (right next to the fridge) to get everything together while the temp differential was most extreme. It got the barrel about 75% of the way in to the receiver before it got stuck. Each part was literally just seconds away from their heat/cold source when it stopped moving. I hammered it the rest of the way with a mallet before the fit had time to get much tighter. Despite the tight fit, that particular barrel wasn't a great shooter, whereas all the others were solid performers.