BCM Lower not compatible with PMAG Gen3

[BravoCompanyUSA]

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 of any manufacturer, and not in others of any manufacturer. 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 just 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.




Thanks for reading,
Hope this info helps.

[Doc Safari]

In support of your position, Bravo Company, I just finished reading this a few minutes ago:

http://www.thefirearmblog.com/blog/2...ont-use-pmags/

PMags are problematic in several different rifles, not just BCM, and not just AR's.

My take: I'm rethinking this; it's not a BCM problem. I think MagPul is in denial about just how compatible their mags really are. I'm going to go out on a limb and say that the over-insertion tab is a bandaid solution to a design that is not perfect.

Seen here is a few examples of when a PMAG has to be manually removed: a problem that isn’t present most of the time with plain old aluminum magazines.

Next up is damage to the SCAR.

Using PMAGs can actually do irreparable damage to an FN SCAR rifle.

The mags cause the bolt catch to rise ever so slightly and drag on the bolt lugs, which results in significant damage over time.

PMAGs are pretty notorious for not wanting to work in various platforms, including guns like the HK-416 and M27-IAR.

Note here that this PMAG will not insert into this civilian version of the HK-416, due to the odd body geometry.

Also, PMAGs had trouble fitting in firearms like the British SA-80/L-85, and will not fit in the FN FS-2000 without the user modifying the weapon by removing a component that serves to seal the weapon from dirt and debris.

To my knowledge, no PMAGs will work in the FS-2000 to this day without modification.

[Bolverk93]

"The Magpul GenM3 PMag was the only magazine to perform to acceptable levels across all combinations of Marine Corps 5.56mm rifles and ammunition during testing. That magazine has, therefore, been approved for use for both training and combat," Marine Corps Systems Command (MARCORSYSCOM)"

"GENTEXT/RMKS/1. PURPOSE. THIS MESSAGE PROVIDES UPDATED GUIDANCE REGARDING THE USE OF MAGAZINES FOR THE M4/M16 SERIES AND M27 INFANTRY AUTOMATIC RIFLE (IAR). 2. BACKGROUND. MARINE CORPS UNITS WILL NO LONGER RECEIVE THE LEGACY MAGAZINE WHEN ORDERING NATIONAL STOCK NUMBER (NSN) 1005-01-561-7200; THIS NSN WILL DEFAULT TO THE U.S. ARMY ENHANCED PERFORMANCE MAGAZINE (EPM), NSN 1005-01- 630-9508. AUTHORIZATION TO USE THE EPM FOR TRAINING USE ONLY WITH THE M4, M4A1, M16A4, AND M27 REMAINS THE SAME. 3. ACTION 3.A. PM IWS AUTHORIZES UNITS TO USE THE FOLLOWING POLYMER MAGAZINES WITH THE M4, M4A1, M16A4, M27, AND M249: NSN 1005-01-615-5169 (BLACK) AND NSN 1005-01-659-7086 (COYOTE TAN). UNITS ARE AUTHORIZED TO REQUISITION THESE MAGAZINES WITH UNIT FUNDS. 3.B. PM IWS WILL UPDATE SL-3S FOR THE M4, M4A1, M16A4, AND M27 TO LIST THE ABOVE POLYMER MAGAZINE NSNS. NO OTHER POLYMER MAGAZINES ARE AUTHORIZED FOR USE. 4. IOT PROVIDE IMMEDIATE AND SUSTAINING ACCESS TO ALL USERS, A PUBLICATION CONTROL NUMBER (PCN) WILL BE ASSIGNED TO THIS MESSAGE FOR ACCESS VIA THE WEAPONS SYSTEM ID NUMBER SEARCH IN SL-1-2.// "

The truth is when I spend my own money on mags I buy Lancer mags, but I have a crap load of pmags.

Out of hundreds of Colt rifle's where I work we have no issues with PMAGs.

My take away from this experience is BCM is not at the same level as Colt or other top level manufacturers. I will get rid of this lower, and move on. I'll also refrain from future purchases of critical components manufactured by BCM.

Not trying to shit talk at this point but my BCM factory BFH upper is the least accurate out of two uppers built with Noveske barrels and an upper built with a Colt barrel.

I do love BCM's charging handles, grips, and VFGs.

[HeruMew]

Moral of the Story:

I am glad I just stuck to buying reputable GI mags.

I have a few PMAGs, some the Second Amend mags, but overall. I just stick to what I have the most invested in: Aluminums.

In the SHTF scenario, I hope my lower will fit, but I also know it likely wouldn't be a fantasy game-like situation where I'll be ripping clips off dead enemies going for a 25 kill streak for the Tactical Nuke.

ETA:
Ironically, I can thank Adams Arms for selling me my first AR with aluminum Colt Mags.

[JediGuy]

After reading through this thread and a detailed prior thread including a Magpul response, I will certainly be checking this when my new BCM lower arrives at the FFL in a couple days. I understand that this isn’t a BCM fault, and I appreciate their response here, but if the lower doesn’t function with my Pmags, I’ll return it to Primary Arms and order a less expensive Sionics. I fall to the side that one of these items has a government contract for use in battle en masse, and I would want my equipment to match that, if reasonably possible.
I hope mine is in the functioning range, as it seems that most BCM lowers really don’t have this issue.

[Beat Trash]

Beat Trash had the same problem a few years ago.

https://www.m4carbine.net/archive/in.../t-169913.html

I had this issue in 2015 when putting together a gun to be used as a personally owned/departmentally approved patrol rifle. The lower I bought was going to be paired with a BCM factory assembled upper. When I observed the issue with the MagPul M3 magazines not seating properly, I contacted BCM's customer service, hoping the issue would be resolved. To their credit, they had me ship the upper and lower back for inspection.

The upper and lower were returned with a note saying they were within spec for BCM. The note stated that portion of the forging that was an issue was not part of the original TDP, therefore, they did not consider it an issue, so long as one used Mil spec magazines. I called the CS department back and was given the same information about only using mil spec magazines in their lowers. Once that was said, the CS rep proceeded to convince me that I should purchase and use the Tango Down ARC magazines that his company sells (Not a Mil Spec Magazine...).

My agency had around 300 S&W M&P15's fielded at the time. And the agency was transitioning over to the MagPul M3 magazine (They have since purchased a substantial amount of additional rifles). These guns didn't have an issue with the MagPul M3 magazine, nor did any of the Colt 6920's in my safe. When I mentioned that during my conversation with the CS rep, he proceeded to share his opinion on why an agency should never issue the M3 magazine as it's a liability issue that could get people hurt or killed. I distinctly remember this conversation when I first read that the Marine Corps was adopting the MagPul M3 magazine as their go-to issued magazine. As a Former Marine, I tend to believe the the Marine Corps knows a thing or two about small arms. Apparently they do not think the MagPul M3 magazine is a liability issue.

I realize that now, as well as in 2015 when I started the linked topic that there are a lot of BCM supporters on this site. I actually caught a lot of hate for starting the original topic. My intent then was not to bash a company, but to let other consumers know of a potential issue. Especially any fellow LEO's who planned on using this product as a Patrol Rifle. BCM can make some outstanding products. In 2015, I owned two of their factory uppers built around their ELW barrels and using their gunfighter comp. The paring of the two made for an excellent upper. But my personal experience in dealing with their company, especially the followup phone conversation I had with their CS, left a very bad taste. so much so that I should off every BCM product I owned.

If you own a BCM lower that will seat a MagPul M3 magazine, or if you own a BCM lower and never intend on using a MagPul M3 magazine, more power to you. I'm sure it will give you good service. But after my personal experience when dealing with their company, I will not purchase another one of their products. When officers approach me for recommendations or advice, I can not in good faith recommend BCM after my experience. Especially when working for an Agency that issues the MagPul M3 magazines.

[Doc Safari]

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.

Attachment 51043

We've seen this photo now, and a diagram posted by Bravo Company.

Note how in the photo the front trigger guard portion of the receiver clearly protrudes past the trigger guard on the receiver that is a "No Go" with Gen 3 Pmags.

I'm wondering if this photo is a "ballpark" approximation of whether a Gen 3 PMag will work in a BCM lower without having to get out the calipers and take measurements. In other words, if you own a BCM lower, it would be helpful to know if you can purchase Gen 3 PMags for it before you place an order.

Is that photo enough that you can get out your own BCM lower and "eyeball it"?

How about it? Is this photo a good rule of thumb? Or does it take actual measuring?

[themonk]

First off I love BCM and use a 11.5 BCM as my go to upper. Its sits on a Umbrella Corp lower for just this reason. Personally I think this war is lost. BCM, KAC and any other lowers that have any issues with gen 3 pmags in anyway need to solve this issue like Noveske did. If I was BCM I would be pissed but now that they are issued the conversation should be over.

[Doc Safari]

First off I love BCM and use a 11.5 BCM as my go to upper. Its sits on a Umbrella Corp lower for just this reason. Personally I think this war is lost. BCM, KAC and any other lowers that have any issues with gen 3 pmags in anyway need to solve this issue like Noveske did. If I was BCM I would be pissed but now that they are issued the conversation should be over.

I hate to say it, but I tend to agree.

Magpul mags are ubiquitous: it's unlikely that will change. They are not some niche accessory. They are more than mainstream, warts and all.

If BCM were dedicated to making a 100% milspec weapon I might think that they are right to stand their ground and stick 100% to print. HOWEVER, I just bought a BCM lower with the Gunfighter stock, BCM polished nickel teflon BCG, and Mod 3 pistol grip. The upper came with the gunfighter compensator.

Clearly none of these additions are what you'd find on a dot-mil-issued weapon (unless I'm horribly mistaken), so BCM is basically conceding that not every component has to be 100% what the military issues. These are fine accessories, but they are NOT what you'd find on a strict military configuration. (Again, unless I'm totally mistaken).

Therefore it's not that much of a stretch for BCM to start making lower receivers with a slight modification that isn't technically "milspec."

I would think that this controversy over Pmags would end up costing them sales. Just read some of the replies to this thread. They would be smart to allow this one deviation to their copy of the TDP in order to please customers. As I pointed out in the accoutrements added to my rifle above, they have already set the precedent to deviate somewhat from strictly military configuration.

Yes, it sucks to have to change a dimension or two just to accomodate an accessory, but it sounds like that's what the market will bear.

MagPul made their Gen 3 mag to work in a lower receiver of Colt specs, right or wrong, and that is becoming the acceptable standard just because Pmags are everywhere and not going away anytime soon.

I realize this could result in a major supply or manufacturing change on BCM's part: not a cheap prospect. But the alternative might be to gain a reputation for not working with magazines that have taken over a huge portion of the market.

As an analogy, imagine an AK that only works with bakelite mags even though cheap steel surplus mags are everywhere and you can see how that would hamper sales of that particular weapon.

[Todd.K]

We live in a World made to a dimension with a tolerance.

BCM just tells it like it is, and knows what the spec is to back it up. Most have no idea what the spec is, will test fit a mag in a replacement lower, and hope you don't complain about them on the internet.

Now imagine both are waiting on a single part to come in so they can ship a large rifle order. Who is going to ID parts that are out of spec? More important who do you think will send those parts back and wait for parts that are in spec?