BCM Lower not compatible with PMAG Gen3

[Wake27]

Here's a crazy thought...just buy M2's. Their cheaper too.

They’re*

And you should probably do some more research on the M3 mag.


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[ace4059]

"Pretty much" and "just about" is not how anything is made to a standard. I'm a machinist, I make parts to a print with dimensions and an allowable tolerance. It's a Engineer's job to make that tolerance reasonably large to keep the price low, while being fully functional in relation to other parts and their tolerances.

If I make a pile of parts most of them will be right about in the middle of the tolerance (if I do my job right) but that doesn't mean that the few that use almost all of the tolerance are wrong. It either meets the print spec and is 100% good or it does not and is 100% bad.

I’m not talking about industrial standard as a spec, I’m talking about industrial standard as in it is THE magazine that’s excepted as the standard in today’s time and it’s THE magazine as all others are judged by. It’s the magazine of the time in the civilian world

[17K]

I have a KAC lower that does not accept NHMTG mags, but works with every p-mag I own.

I'd let KAC know about that. NHMTG and Okay are the same mags and the same mags that KAC uses.

[usmcvet]

What came first, the AR15 lower and the dimensional specification required for it to function correctly or the Gen 3 Magpul magazine? Personally, BCM is still good to go in my book. YMMV. Is over insertion an issue generally? I’ve never experienced it? Mine works with Gen 3, but I have enough Gen 2’s that I don’t think I ever need to worry.

I've seen it twice and it was with a P Mag in an old Colt M16 lower(serial. Number 330,000 range) with a a a BCM upper. UNK what generation. The malfunction it caused was a complete Cluster and needed tools and quite a bit of time to fix. The rounds were on top of the BCG. Is this a PMag issue?


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[17K]

I had a couple of BCM lowers a few years ago that wouldn't accept M3s.

I don't think BCM's not Mil-Spec excuse holds water. If the mahs weren't compatible with the entire spec range of Mil-Spec lowers, then the military would have to weed out all their non-compatible lowers to use 'em.

[mack7.62]

Yeah not digging the BCM response in 2018 after Gen 3's being around since 2011, here is a Magpul comment from 2012:

"I asked Magpul’s Drake Clark about this issue. He made this statement …

The M3 design was based off years of feedback from endusers. We knew going into the design phase that there are some lowers that are not going to work with the M3 as the magwell spec they are built to is different from the original Colt design, specifically in the area where the over travel stop interfaces with the area just forward of the trigger guard. These lowers represent less than 1% of the total lowers in the marketplace. We already had direct communication with a few manufactures who build lowers with conflicting interfaces, including POF. Changes will be made to their design to allow comparability. When these changes will be introduced into full production I am not sure. I can say some that have recognized this issue have already been addressed it, such as Noveske.

And for those that have older design lowers that are not comparable with the M3, they have two choices. Use the MOE PMAG or modify the M3 by removing the over travel stop to allow for proper interface.

In all fairness to Magpul, the M3 is compatible with more firearms than any of their previous PMAGs. For >99% of users this will not be a problem. I expect the few manufacturers who are producing incompatible designs will soon change them, it being an easy issue to address."

[MWAG19919]

The reason it is “more flared” is because there is more material hanging down to flare. If it was the same as the colt then the flare would be the same.

I think if you buy a non blem lower it should work with a gen3 pmag. Pmag is an industrial standard. Hell, they maybe more popular than aluminum mags. Basically if we as a forum stop accepting BCM’s excuses then they would have to change it. I’m a bcm fanboy but if another company had this problem, especially ones m4 looked down on, this site would be bashing the shit out of that company. Let’s get real people.

Due to the thread from ‘15 I haven’t purchased any other BCM lowers. They have lost several sells from me due to their response. But now I several battle arms, and colt lowers that work perfectly with pmags. CS makes or breaks a company.

FWIW my BCM that works with M3 PMAGs is a "blem" lower that was bought from Grant. I'm not sure there's even a blemish on it to tell you the truth.

[0uTkAsT]

Just to add my two cents, my BCM lowers, both manufactured 2016-later, have no compatibility issues with any of the dozens of 20, 30 or 40 round M3 PMAGs that I have.

[JediGuy]

Since I mentioned I would be purchasing a lower, I wanted to follow up on that.

I received the lower and tested two 30rd and one 20rd M3 PMAG and all locked in easily and smoothly. No problems at all. BCM responded very quickly (before 0700 after my email at 2229) to my inquiry, and they stated a manufacture date of February 2017.

[TopPlinker]

My findings: I just got last night from my FFL a transfer on a brand new BCM Lower I purchased last week and I tested my older BCM Lower (Nov 2015) and both accept all my Magpul M3 Mags and I tested 10rd, 20rd, 30rd, 30rd Window, 40rd, 30rd 300BLK and a D60. Both lowers worked great with them all and did not seem tight when locking up and all the stick mags dropped free easily when empty. In fact the bigger ones shot out of the magwell better than my other lowers. I did not try the D60 for drop free.

The other people that shoot BCM Lowers ~3-4 people at matches over the past 2 years at my club also have run M3 40rd mags and they all seemed to work just fine. So I assume it is most likely a small subset of there lowers that are having issues. Would be nice to figure out how small or large that subset is though.