BCM thermo fit upper fun

[mv1arms]

Installing the thermo fit blem upper from BCM was quite a challenge. Took about 10 iterations of cooling the barrel extension under the cold water faucet, then quickly heating the upper receiver, and pounding on it with a mallet to get the barrel in. I also used some green loctite 620.

The barrel is proof research stainless and the extension measured at 0.9995. The inside of the receiver was 0.9990 before ceracote.

Looking forward to some accuracy testing with it because that thing isn't getting pulled any time soon. It wasn't very fun to install!

[BlogSarge]

[mv1arms]

I think the inside was ceracoted, ya. I probably should have requested that be left alone.

[mv1arms]

Oh I should also mention that my factory criterion barrel was a very sloppy fit inside the BCM upper and slid right in. I couldn't shoot anything under 1 inch with that barrel.

[BlogSarge]

I think the inside was ceracoted, ya. I probably should have requested that be left alone.

Well, at least you have a tight, solid fit!

The proof will be in the precision. Post up to let us know how it does.

[rabiddawg]

[A5BLASTER]

It's like someone should have told him that you have to freeze the barrel. And to lose the stupid glue.

[mv1arms]

Three cold water actually helped because after a while the barrel extension would heat up and the thing would no longer budge. Definitely doing the freezer next time.

[Old Bob]

Three cold water actually helped because after a while the barrel extension would heat up and the thing would no longer budge. Definitely doing the freezer next time.

I recently installed a loose fitting barrel using the thermal method & .002" stainless steel shim stock. The cold barrel went in only so far into the heated upper before I could no longer push them together by hand. It was about a quarter inch shy of being fully inserted so I threaded on a barrel nut & used that nut to pull the barrel the rest of the way into the upper. Torqued to 45ftlbs it's a good, tight, solid connection. Here's hoping it will shoot gnat's eye groups.

[StoneHendge]

Luckily you have a Proof barrel and you won't have to pull it because chances are you won't get it out. When the barrels shot out, it will make a unique tomato stake with the receiver on top.

[mv1arms]

unique tomato stake with the receiver on top.

No doubt

[BlogSarge]

The freezer for the barrel and a heat gun for the receiver are the way to go. Or just leave it outside like I did last winter. It got down to about 10 F. I used a paint stripping gun to heat the receiver til it was good and hot. The barrel slid right in kind of snug. After a few seconds the barrel was in for good.

If it ever needs to come out, a suitably sized dowel in from the rear of the receiver and a small sledge should do it.

[PVBoom]

I think the inside was ceracoted, ya. I probably should have requested that be left alone.

Um, irrelevant.
BCM uppers (and Noveske, VLTOR, JPE) are machined to require thermal fitting.

If you are getting one, you will be thermal fitting, and using any simple liquid to chill the barrel is a waste of time.

[mv1arms]

Um, irrelevant.
BCM uppers (and Noveske, VLTOR, JPE) are machined to require thermal fitting.

If you are getting one, you will be thermal fitting, and using any simple liquid to chill the barrel is a waste of time.

Ceracote adds 0.001 thou so not sure how that's irrelevant. Also thanks for explaining that the method that worked for me was a waste of time, very helpful.

[tdbru]

if it's available, LN2 works pretty well at chilling things down. otherwise a deep freeze makes the barrel cold enough it hurts to hang on to it with bare hands.
-tdbru