RFI: BCM 11.5” GTG?

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Originally Posted by Wake27

I love BCM but they sound like they may not be the most balanced on gas. From what I’ve seen and heard (no personal experience) they have produced 11.5 carbine barrels with gas ports anywhere from .073 to .076. The former is likely a good balance but the latter is probably overgassed. I have no doubts that it’ll still work but personally I’d prefer it on the smaller end. I don’t know if these are normal variances (doubt it) or they went from one to the other over time and if so, whether they opened it up or shrink it down. I do know that several people have asked and BCM refuses to answer.


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I've experienced that variation in gas port sizes first hand. The .073 was on a .625" ELW barrel and the .076 was on a .750" govt profile barrel. The only explanation I could find is an old thread on either LF or M4C that alluded to the theory that they went with the larger port on the larger diameter barrel to offset the gas traveling that extra .0625" through the gas port. That was a theory and not from BCM.

It makes sense, but at the same time seems like it wouldn't or shouldn't matter unless it was on the ragged edge of reliability, which anything with a .07 measurement on an 11.5" barrel is certainly not on the edge of reliability.

@Totem Polar every BCM upper I have owned has been great, even if they are a little generous with the gas port. It's not that bad, and nothing like the OG MK18 with the .082" gas port that chewed through gas rings every 2500 rounds. If you find one I think you'd be well served by it.

With that said, my 6933 absolutely dunked on the BCM 11.5" uppers I had. It was softer shooting while still maintaining reliability across many different ammo types, and consistently held tighter groups at 100.

Good info. The one I had a line on sold (go figure), but they’re a notch up on the watchlist over the general opinion here.

I've got a brand new 11.5" BCM ELW fluted barrel in the mail that will end up posted on the EE when it arrives. Just in case anyone needs one and wants to save me the restocking fee . . .

Not sure if this type of post is permitted outside of the EE - apologies and please let me know if not.

I bought an 11.5 BCM pistol and SBR'd it. I really like it so far, no issues.

https://i.imgur.com/uZzOgoe.jpg

My N of 3 BCMs that were purchased over the past 7 years or so have been outstanding. BCM is one of the best values out there, IMHO.

I've got the lower, still trying to track down a BCM 11.5 upper.

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Originally Posted by RancidSumo

I've got a brand new 11.5" BCM ELW fluted barrel in the mail that will end up posted on the EE when it arrives. Just in case anyone needs one and wants to save me the restocking fee . . .

Not sure if this type of post is permitted outside of the EE - apologies and please let me know if not.

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I may be interested

Would I be too hipster for saying get a 12.5? I just don't see the point of going less than that and not having 300 BLK unless cost is a factor.

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Originally Posted by Mike C

Would I be too hipster for saying get a 12.5? I just don't see the point of going less than that and not having 300 BLK unless cost is a factor.

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A 12.5 won't fit in my backpack.

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Originally Posted by Casual Friday

A 12.5 won't fit in my backpack.

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Bummer, but I completely understand.