Thoughts on BCM blem upper receivers? (2024)

Thinking of using one of these to build a short 5.56 upper. I have used a couple of the standard BCM upper receivers and they have always been great. What is your experience with these?

Thanks

quiksilv81 said:

I’ve used 3 and all were in great shape. 2 of the 3 I couldn’t really see any blemishes.

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Thats similar to other things i have read online. Thanks for the info.

I bought one and the blemish was insignificant. My only complaint is my barrel (daniel defense) would not fit in the upper, even when heated up first. I put my barrel in the freezer for an hour then blasted the upper with a heat gun. Still no go.

I had to spend some time sanding down the interior of the upper so the barrel would insert. Once it did go in, it almost immediately locked in and wouldn't come out by hand. Going to be a real pain to change if I decide to. Not a big fan of the extra tight fit that BCM intentionally creates.

black5.3 said:

Thanks for the info guys.. the standard BCM upper i built my sbr 300blk with was tight but not like what you described. I smeared a little grease on the barrel extension and had to wiggle it in. It was a good nice fit though. Not overly tight.

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I suspect the daniel defense barrel extensions are slightly oversize for normal uppers to fit snug. So pairing it with an undersized upper made an impossible fit. I did measure it with my calipers, but can't recall exact numbers. It was well over a reasonable interference fit.

lightmup said:

I have built three AR uppers with the "blem" BCM uppers. They have been tight, but I haven't seen any noticeable defects in them. I wouldn't hesitate to build another with them. You can save a few bucks on buying the blems.

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Yeah the blems are about half price and i just have to spend a few minutes installing ejection port cover and forward assist. Great info guys

I've used a handful of them, and chose them specifically because of the tight fit to the barrel extension for accuracy. IMO that is the one thing that sets BCM receivers above most others. Plenty of other uppers are available out there if you want something that fits loose.

All of the BCM blems I bought had scuffs on the left side of the receiver that were visible even after being oiled and rubbed down well, but not through the anodizing so it didn't affect anything. A shot of Krylon "ultra black" camo paint covers it up and blends in well.

KZP said:

I bought one and the blemish was insignificant. My only complaint is my barrel (daniel defense) would not fit in the upper, even when heated up first. I put my barrel in the freezer for an hour then blasted the upper with a heat gun. Still no go.

I had to spend some time sanding down the interior of the upper so the barrel would insert. Once it did go in, it almost immediately locked in and wouldn't come out by hand. Going to be a real pain to change if I decide to. Not a big fan of the extra tight fit that BCM intentionally creates.

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How did you heat the upper?? How long?

I've used 40-50 of these and have another 20 or so in the safe. I have recommended them to.numerous people. Most of.then come brand new in a BCM retail box. A fee come.wrapped in a non labeled box. Only 1 or 2 had a minor blemish I could find.

They are undersized for a nice tight fit. After heating them up on a reaction rod and greasing the extension they tap.right in with a rubber hammer. My go to favorite forged upper.

padom said:

How did you heat the upper?? How long?

I've used 40-50 of these and have another 20 or so in the safe. I have recommended them to.numerous people. Most of.then come brand new in a BCM retail box. A fee come.wrapped in a non labeled box. Only 1 or 2 had a minor blemish I could find.

They are undersized for a nice tight fit. After heating them up on a reaction rod and greasing the extension they tap.right in with a rubber hammer. My go to favorite forged upper.

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Heat gun on high for 8 minutes, had some aeroshell grease I applied but the upper got so hot it was drying up. Even froze the barrel for an hour then re-heated the upper. From what I remember, the difference in size from the barrel extension and the upper was was 0.009" give or take a little. Enough that it wasn't going to fit normally.

Makes me think the Daniel Defense barrels have an oversize extension to fit snug in a normal upper. But when paired with a snug upper like BCM, it was an impossible fit.

I remember the barrel extension fit perfectly in the upper if I slid it in the backside where the BCG goes. So if the BCM was not intentionally undersized, it would have been a perfect fit.