BCM Prototype upper?

[Biggy]

just tossing this out there but these do not work with a geissele rail, the tabs on the lower corners of the rail do not clear the added material on the upper.

It looks like I will be breaking out the file , because to get it to fit the MK16 handguard you will have to remove about .080" thousands of an inch off the inside of both lower anti-rotational tabs, and approximately .015" thousands of an inch off of the inside of both the upper anti-rotational tabs. Yeah, a hassle for sure, but there is still *plenty* of thickness on all the tabs to more than do their job. The bare aluminum where you filed will be pretty much unnoticable on the inside of the tabs,

[hobbes221]

Modding the rail is an option and I agree that it would work and should not be too hard to do but I just wanted to let guys know that its not a drop in. I have a mk16 and 2 mk8 rails and might take a file to one for a test

[26 Inf]

I put an upper together using mine a couple days ago with a Roscoe 13.7" stainless barrel I wanted to try out.

I've used over a dozen of the 'blem' BCM uppers on builds and have never had to resort to heating the upper. I heated this one up and still had to tap the barrel home with a rubber mallet.

Don't know if it was the upper or the Roscoe extension. We'll see how it shoots in a week or so, it's off getting a JP flash hider pinned and welded.

[grizzman]

I forgot to test mine with a Geissele MK4 while I was pairing it with a different upper.

I used it to replace the upper in a MK12 Mod 4. I was surprised to see the MK12's upper receiver had been lapped.

The MK2 upper had a tighter fit than the MK12's, which had a tighter fit than a standard BCM stripped upper. I only needed to heat the MK2.

I've used two MK1s with BCM barrels, without heat required. I was surprised.

[Blackhalo]

I put an upper together using mine a couple days ago with a Roscoe 13.7" stainless barrel I wanted to try out.

I've used over a dozen of the 'blem' BCM uppers on builds and have never had to resort to heating the upper. I heated this one up and still had to tap the barrel home with a rubber mallet.

Don't know if it was the upper or the Roscoe extension. We'll see how it shoots in a week or so, it's off getting a JP flash hider pinned and welded.

Interesting. All my builds have BCM blems and all have had to be heated and tapped home. DDs, FNs and BA barrel.

[rainman]

Interesting. All my builds have BCM blems and all have had to be heated and tapped home. DDs, FNs and BA barrel.

This has been my experience as well with multiple brands of barrels including Colt and Mega to name two.


-Rainman


-Rainman

[26 Inf]

Interesting. All my builds have BCM blems and all have had to be heated and tapped home. DDs, FNs and BA barrel.

I have two BA's installed, no DD or FN. Don't get me wrong, they've been snug, but no heat required.

[alx01]

I put an upper together using mine a couple days ago with a Roscoe 13.7" stainless barrel I wanted to try out.

I've used over a dozen of the 'blem' BCM uppers on builds and have never had to resort to heating the upper. I heated this one up and still had to tap the barrel home with a rubber mallet.

Don't know if it was the upper or the Roscoe extension. We'll see how it shoots in a week or so, it's off getting a JP flash hider pinned and welded.

In my sample of two BCM uppers (new blem and non-blem) vs two Aero uppers (both new):
Aero uppers had a tighter barrel fit and much better lower to upper fit vs BCM. BCM were not a tight fit at all for barrels and were pretty sloppy for upper to lower fit. Barrels tried - BA, Rainier CHF, Colt. At that point I figured that BCM mil-spec uppers were probably over-hyped for what they were and just not worth it for me. Maybe I got out of spec or edge of the spec BCM uppers both times - who knows. Again, this is my personal opinion and limited experience.

I find it disingenuous for BCM to claim that their MK2 upper is fully mil-spec compatible, yet fail to mention that most popular aftermarket rails (Geissele) do not fit. BCM MK2 upper has been seen in a public for at least two years - I find it impossible to believe that BCM did not test with the Geissele rails.

[CrowCommand]

I put an upper together using mine a couple days ago with a Roscoe 13.7" stainless barrel I wanted to try out.

I've used over a dozen of the 'blem' BCM uppers on builds and have never had to resort to heating the upper. I heated this one up and still had to tap the barrel home with a rubber mallet.

Don't know if it was the upper or the Roscoe extension. We'll see how it shoots in a week or so, it's off getting a JP flash hider pinned and welded.

Could be the Rosco barrel, I put my 11.5" Rosco in the freezer for and hour or two to get it to fit into the Aero upper I was building.

[QuickStrike]

Damn, bummer that it won’t work with an LMT mars lower.