In case anyone else wasn’t aware of this. I wasn’t.
Apparently not all BCM lowers are compatible with M3 PMAGs. I just completed a build using a BCM lower. When I took it to the Range I realized that I could not fully seat any of the Gen3 PMAGs I brought. The issue is that this version of the PMAG has a tab on the spine of the mag to prevent over insertion. On this lower that tab prevents the mag from being fully inserted.
I e-mailed BCM about it, and their response was that this sometimes happens with their lowers, and I should only use mil-spec mags with their “mil-spec” lowers. They claimed that there are no tight controls on this area of the lower.
The issue that I take with their answer is that M3 PMAGs are mil-spec in that they have been issued an NSN (1005-01-615-5169) and are approved by the Army and the Marine Corps. In fact the mags I was using were issued to me, and are what all my teammates use in our Colt M4s with no issue. I have also never had issue using these mags with my DD rifles or guns built on Spike’s lowers.
Live and learn. I’ll stick to Colt and Daniel Defense, or even Spikes lowers when I want to build something.
Perhaps I should not have claimed the PMAGS to be mil-spec. I’m not prepared to argue what constitutes mil-spec or not. Regardless they are approved by the USA and USMC, which indicates a certain level functional testing with mil-spec weapons.
The purpose of this thread was really to make people aware of an existing issue.
*Edited to be more cordial.
Looking at MagPul’s description of their M3 mags it states “the GEN M3 is optimized for Colt-spec AR15/M4 platforms”.
Colt-spec is apparently now a thing.
I will stick with Colt and Daniel Defense from now on.
I’m not going to sign up for photobucket.com just to post pictures, but there is a discernable difference between my DD lowers and this BCM.
The DD lowers are flush with the trigger guard at the magwell. The BCM magwell extends a fraction of an inch below the trigger guard.
There is no wearing in of these mags to fit. Also, I have already run thousands of rounds through these mags in my work gun.
Also the M3 magazines state that they sometimes need to be worn in a bit to fit all lowers. It took more than a few times inserting and removing the mags probably several minutes per mag until they fit in all of my lowers.
My BCM has never had a problem with any of my Gen M3 PMAGs, but I’m aware of the issue. At one time I read the entire thread on here about it, and I really wasn’t impressed with BCM’s attitude toward the issue. The mil-spec excuse is pretty lame when Colts don’t seem to suffer the same problem.
Guys,
This is a known issue.
BCM has known about it for a few years and has done nothing about it. They blame MagPul and say there is nothing in the TDP as the length of the magwell where the over insertion tab hits.
If you ask MagPul then they blame BCM for out of spec lowers.
Yes. And probably not.
I’m sure the specs on the pmags have more tolerance than the lower. Out of all the lowers BCM puts out I’ve only heard of this a handful of times so it’s a small percentage. But what gets me is BCM won’t do anything about it. They should machine the back of the magwell to properly length on the forged lowers that are a little off.
I’m glad all my BCM lowers work with gen3 mags or I would be pissed. And the OP should be rightly so. I think BCM is held to a high standard here and they fall short on this one.
I have a KAC like that that I refuse to build out and no one will buy off me for far less than I paid. I have plenty of high end lowers that have no issue with gen 3 pmags. It’s tolerance stacking and in my opinion is BS.
I don’t think there is an issue of tolerance stacking. As previously stated the Army and USMC approved the M3 PMAGs for combat use after thorough testing. I don’t want to talk out of my ass, but I’m sure that potential tolerance stacking issues would be identified. There’s no way they would approve a mag that would fail to function in a percentage of their weapons.
I tried 7-8 M3 PMAGs in the lower in question. They all failed. This lower is clearly off. On all my other rifles the magwell is even with the trigger guard. On the BCM lower the magwell extends below the trigger guard. I don’t want to be a crybaby, but I am dissapointed. Something either meets the standard or it doesn’t. This item clearly doesn’t meet the standard.
I’ll probably either sell this lower or put it on my beater gun.
See the picture below. I should add both trigger guards are the same design. The only difference is the logo on them.
Hell, M3s rack in my cheap crappy plastic 80%s… you know there’s something SERIOUSLY wrong when my $25 Bubbafied homebrew EP Armory plasticrap works and your expensive BCM doesn’t.
Not to diss BCM, the parts I’ve bought from them I’ve been impressed with and I’m thinking about asking them if they can do an unassembled “kit” version of their C8 URG for the GF… but there’s just something head-scratchingly “WTF?!” with them on this one.
This is the first I’ve heard of this, and I have quite a few BCM lowers (and quite a few gen 3 PMAGS). I’ll have to grab an empty PMAG and try all my lowers.
