BCM Lower not compatible with PMAG Gen3

[26 Inf]

Just to be clear, I'm a bcm fan. Will buy and recommend anything they make, except for their lower.

In two posts you've mentioned 'anything they make.'

I'm curious just how much some of the companies actually 'make' versus 'have made' versus 'assemble from OEM sourced parts.'

I'm sure in most cases, either way, it's all good stuff, but in some cases we might begin to wonder were the extra 400 to 500 dollars worth of value lives in Brand A versus Brand X. Or the extra 20 to 30 bucks in the LPK.

[26 Inf]

Well I'm sure you can go back to your PSA budget build forum if you like.

Edit: Not relevant

[wetidlerjr]

PMAGS I and PMAGS II fit BCM lowers. MAGPUL makes PMAG III and now a few (but not anywhere near all) don't fit BCM lowers that haven't been changed. PMAG III aficionados and mavens now declare BCM must change lowers. MAGPUL doesn't have to change anything and can do no wrong.
Old saying; File on the cheap part.

[themonk]

I sent BCM an inquiry about this issue and this is their reply:

Hello,



Thank you for contacting us.



The M3 version of the PMag adds an “over insertion tab” on the rear spine of the magazine. Unfortunately, it interfaces with an area of the lower that can vary substantially during the manufacturing of a milspec lower receiver group.


For this section of the weapon you have 2 sets of tolerances; forging tolerances and machining tolerances. When you add them up the Mil-Std TDP finished product has a range. For over 5 decades, the dimensions controlling the lower end of the magwell have been generous with tolerances. Allowing as much as +-.060” of tolerance in the M16, and even more within the M4 requirements, with the majority of the tolerances in the forging. That means lowers can vary by 1/8” in this area!



BCM lower receivers are built within the semi auto versions of those prints. Any AR15 lower built to the correct print could still have this issue with the over insertion tab.

It is not fully backwards compatible. Based on our analysis, the location of the tab is based on a lower built to the center of the tolerance range, which leaves the possibility of up to 1/16” of interference in some cases. We have gone over the documents many times to ensure this is not an oversight on our part. If it was, we would scramble to make it right. We have not found this to be the case though. Due to the allowable tolerances in the mil-spec prints, the tab will work with some lowers, and not in others. This is not specific to BCM and similar situations will arise from many other makers whose tolerances may even exceed the TDP allowances.



The PMag is obviously an excellent design, but this tab has the possibility to cause issues with any milspec lower. As a result it is possible even within the same manufacturer to have it fit some and not on others. If you want an inventory or load out of fully cross compatible mags we recommend you file off a bit of that tab, because while it may fit in the couple of your lowers, and then it may not fit in the next couple of your buddies AR.



Please let us know if we can further assist.



Bravo Company USA, Inc

I liked BCM products, but at this point I will no longer recommend their products to any of my friends. I just don't want them to have to go through the same thing I am going through now.

Awesome that they now have a form email for the issue.

I have a feeling this would have been fixed already if Pat was still alive. I am disgusted they are still fighting the issue.

[GH41]

PMAGS I and PMAGS II fit BCM lowers. MAGPUL makes PMAG III and now a few (but not anywhere near all) don't fit BCM lowers that haven't been changed. PMAG III aficionados and mavens now declare BCM must change lowers. MAGPUL doesn't have to change anything and can do no wrong.
Old saying; File on the cheap part.

I agree. If you put enough $$$ in marketing you can make half the world believe anything! With the exception of a handful of Lancers I transitioned away from plastic magazines years ago. Mil spec OKAY magazines work in every lower I've tried including BCM. Since when did MagPul magazine become mil spec??

[themonk]

Since when did MagPul magazine become mil spec??

When they started being issued to troops.

[wetidlerjr]

Originally Posted by Bolverk93
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.

Originally Posted by Renegade
Being MIL-SPEC and being issued are two different things.
PMAGS are not MILSPEC nor are they STANAG 4179 compliant.

Originally Posted by GH41
Since when did MagPul magazine become mil spec?

When they started being issued to troops.

Hmmm...

[Pokgai]

Hmmm...

I think for my personal usage as a SHTF rifle, I don't really care if a type of mag is mil-spec or not, but rather how widely spread its market is. If 90% of the population is using one type of mag, I better make sure my rifle is compatible with that type of mag, mil-spec or not. If only 10% of the population is using one type of mag, even if its mil-spec it wouldn't be on my priority list for compatibility.

[themonk]

Hmmm...

Bill I retract my comment. It was based out of being lazy. Milspec is not the proper term. They are being issued. They DO NOT have any issue with any Colt or FN lowers I have seen or handled. I think it is likely that pmags will become the new standard. Some may like it and some may not. I don't really care and I personally think that the 3rd gen pmags suck. But it doesn't change the fact if you make a lower that is tier 1 or battle ready you lost the battle and your lower should now work with gen 3 pmags. Carrying around a file to alter any said pmag to fit you gun when you need it is ludicrous.

[wetidlerjr]

Bill I retract my comment. It was based out of being lazy. Milspec is not the proper term. They are being issued. They DO NOT have any issue with any Colt or FN lowers I have seen or handled. I think it is likely that pmags will become the new standard. Some may like it and some may not. I don't really care and I personally think that the 3rd gen pmags suck. But it doesn't change the fact if you make a lower that is tier 1 or battle ready you lost the battle and your lower should now work with gen 3 pmags. Carrying around a file to alter any said pmag to fit you gun when you need it is ludicrous.

I haven't had any problems with IIIs and my BCMs but it is probably just as ludicrous to expect someone to mod lowers they already have to accomodate a mag. PMAG IIIs changed; BCM lowers didn't as far as I can tell. Boils down to a "blame game" I guess and like you, I don't really care all that much either.