Problem with a new BCM lower

AR/M4 AR Technical Discussion
1

I could use some advice.

I bought a complete BCM lower receiver (not a blem). I paired this with a factory built BCM upper (14.5” ELW-f with a 13” KMR rail and BCM BCG).

From a closed bolt, this setup would not permit a fully loaded PMAG (verified 30 rds, not 31) to be seated. Several different magazines tried. All magazines tried functioned in DD and Colt factory guns.

I contacted BCM and shipped the lower back to them. They eventually returned the lower, shipping it to my FFL instead of me. (Not a requirement as they are the manufacture and I already own the lower) This generated a second transferee fee.

There was no notation as to what was discovered, no communication from BCM, just the same lower returned to me. It would now seat a loaded PMAG, barely, with a closed bolt.

Yesterday was the first time I had a chance to shoot this gun. With the magazine seated on a closed bolt, and loading the gun by working the charging handle, it would fire that round, but it would not pick up the next round in the magazine. This continued to occur even as rounds were taken out of the magazine, as in it occurred with 30 rds in the magazine or even with 25 rds in the magazine.

Just to ensure it was not a magazine issue, I also had two Daniel Defense guns and a Colt 6720 with me. I tested the magazine in the other guns, no issues.

Before anyone tells me to load from an open bolt, or to download magazines, etc, this gun was intended to be my new “patrol rifle” while at work. Department policy mandates a fully loaded 30 rd magazine, and the gun to be stored in a manner referred to as “cruiser ready” which is bolt forward on an empty chamber, safety on and a magazine in the gun. Activate the charging handle to chamber a round as needed. Carrying a gun in this manner is not an issue with my personally owned DD or Colt guns. Nor is is an issue with the agency owned S&W or even the older Bushmaster guns.

As it is, I can not trust this gun for it’s intended purpose if I can not guarantee the second round will actually chamber after firing the first round.

The upper used was tested on a different lower receiver, and performed without issue. So I assume the issue is not with the upper receiver.

Any ideas of what the issue might be? I assumed initially it was a slightly out of spec lower receiver. But…?

2

Have you tried any other magazines besides P Mags? It does sound like something is slightly out of spec with the lower.

3

I would try a few other magazines, but yes, it really sounds like something is out of spec with this lower.You did the right thing by contacting BCM before addressing it on here. Hopefully some pros can nail down whats up.

4

Possibly try swapping the Colt magazine release assembly with the BCM and see if that affects the problem.

5

My intent with this topic is not to bash BCM. My intent was to see if the collective expert wisdom that is out there has ever ran into this type of thing.

I have decided to send it back to BCM one more time to see what happens. The customer service at BCM answered quickly to today’s email and they want to “aggressively look into the issue”.

Until then, I will ask the moderators to close this topic, as I don’t want the impression that I am bashing BCM in the internet. I’ll reopen this once they have another chance to look over the gun.

6

Honestly though, with how you worded everything I am not sure anyone here will think you were bashing the company at all.

7

Anxious to see how this turns out. OP, I’d not fiddle with it. Let BCM fiddle with it. They sound ready and willing.

8

I don’t think it was bashing, but let’s allow them an opportunity to address it again.

9

I asked that this topic be reopened as I have sent the lower back to BCM and they returned it.

As I mentioned in the original post, the BCM lower would not reliable seat Gen3 PMAG’s. Also, depending on the particular gen3 PMAG, the magazine sat just low enough that the second round would not be picked up after firing the first round chambered. The amount of rounds in the magazine were not a factor.

Off the lower went to BCM for a second time. This time, I received a phone call from someone from their Customer Service Department. After a lengthy conversation, he sent the lower to his engineering department. They stripped the lower and measured it. The attached note from the engineering department stated that “since this was a mil spec lower receiver, BCM only recommends the use of mil spec magazines for proper function”.

The CS rep stated that the lower was measured and that all measurements that were part of the TDP were with in spec. He said that there was a variation that naturally occurs during the forging process in which some forgings are slightly larger than others, and that although this lower was on the longer side, it was still within their spec’s. He was referring to the measurement from the area of the lower where the trigger guard mounts on the back of the receiver, to the bottom of the magazine well. Since this measurement was not part of the original TDP, they deem it to be acceptable. As the original magazine spec in the TDP did not include an anti-insertion tab, their stance is that the issue was with the design of the PMAG, and not of their lower receiver.

The problem is that the part of the lower in question is just long enough to hit the over-insertion tab on the gen 3 PMAGs. He said this issue occurs with any and all manufactures. I explained that I also own a couple of DD guns, as well as a couple of Colt 6920’s. In addition, I took the magazine that would not seat into this BCM lower to work and tried it in 6 different Agency owned S&W AR’s that I picked out at random. No issues with any of them seating the gen3 PMAG.

The CS rep was convinced that the issue was not with his product, but with the design of the gen 3 PMAG. He spent the majority of the conversation trying to convince me why the gen 3 PMAG should not be used in a carry/duty gun. Or that if I really needed to use gen3 PMAGs, that I should grind off the anti-insertion tabs on all of the mags first. They shipped the gun back to me, along with a hat.

I had planned on using this new receiver/upper combination as my Patrol Rifle at work. My agency issues gen 2 PMAGs with their pool rifles. I’ve been using the gen 3 mags since they came out and own more than a few gen3 PMAGS. Now the concept of owning a carbine that can’t use the same magazines as the rest of my guns, or that needs modified magazines to function just doesn’t sit well with me at all.

I struck out with BCM’s customer service. Big time…

The two BCM upper assemblies I purchased were my first venture into buying anything from BCM’s product line. These upper assemblies had me excited. My experience with this lower has left me extremely disappointed with the company. Not only did they loose a customer, but I can not in good faith recommend them to any of my officers.

I am going to sell off this lower (with full disclosure) and eat any loss. But I need another lower receiver to pair with the soon to be lowers upper.

Choices of reputable branded lowers are rather slim at this time.

DD doesn’t sell separate lowers.

Colt doesn’t either. I guess I could buy a complete Colt, like one of their 6920-OEM1 and sell off the upper. But that’s more hassle than I have time for right now.

Noveske sells stripped lowers. But I am looking for a complete lower.

While S&W does sell complete lowers, I’m not in a rush to go that route. My agency has about 250-300 S&W carbines as pool rifles. They have their own issues at times.

LMT sells a complete lower called the “Defender” for a price that is competitive to the BCM. Right now, this LMT lower receiver seems like the best option. But I have zero experience with the LMT rifles or lowers.

Does anyone have any experience with the LMT Defender complete lowers? Are they comparable with gen 3 PMAGs? An just as important, can anyone comment on LMT’s customer service?

Any other thoughts?

10

I have two BCM uppers purchased separately that I mated to two BCM complete lowers. They are tight and run Gen3 Pmags flawlessly. I am very surprised to read this based on my experience. I would ask BCM for a replacement lower.

11

Sorry to hear about your issues. Regarding the LMT lower, I have one and I recommend it. They use good parts in their lowers just switch out the buffer to what you normally run as they come with a carbine buffer. Other than that my experience with 2 LMT uppers and 1 lower has been great. My rifle I have now is all LMT and I’m satisfied. No issues seating a loaded gen 3 PMag on a closed bolt.

12

I’m honestly very surprised to hear this result. This certainly isn’t the BCM CS we are used to hearing about. I know this is one a single issue, but I hope this isn’t a foreshadowing of what is to come from BCM.

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13

LMT lowers are good to go. I have two that I Form 1 SBR’d and they are fine with Gen 3 PMAGS, as are all of my other lowers, including a BCM. Sucks that they treated you like this. KAC lowers are where it’s at IMO.

14

I asked for a replacement lower and was told that it was in spec as far as they are concerned.

Will decide tomorrow if I want to go with a LMT lower or buy a Colt 6920 OEM-1, and sell off the upper.

I found someone who doesn’t use gen3 PMAGS who is willing to buy my BCM lower. He’s a friend and there is full disclosure. And he’s getting a deal.

I too have heard great things about BCM’s customer service. Hence my extreme disappointment.

15

I would call again and try to get a different rep.

16

Would it be possible to file away material from the lower to make it function? I’m not familiar with exactly where the anti insertion tab interfaces. Sure it isn’t ideal or cosmetically pleasing, but neither is spending more money or time. That said, I’m surprised that BCM won’t make it right, as pmags are ubiquitous.

17

I don’t understand what BCM did wrong. They told you the receiver you have doesn’t like gen 3 Pmags but is within spec. If it works with mil spec magazines how can you fault BCM CS? I do understand your reason for selling it.

18

Have you tried gen 2 pmags? I have a colt that didn’t want to seat gen 3’s, but the gen 2’s work perfect.

19

It will work with gen 2 mags.

BCM’s engineer stated their “mil spec” lowers should only be used with “mil spec” magazines to ensure proper function. Yet the CS rep after explaining why the MagPul gen3 was such a bad design, uses TangoDown ARC magazines. A non-mil spec magazine.

They did not say the lower was in spec. They said that the parts of the lower receiver referenced within the TDP was within spec. They are the ones who determined the crucial measurement which prevents the use of gen3 magazines was “Long”. But if I were to buy another BCM lower, odds were that the next one would work with gen 3 PMAGs, due to the variance of the forgings they use. When I replied, “So it’s a crap shoot then?” The response was, “yes”.

One gen3 magazine would seat, but when shooting the gun, the second round would not be picked up after firing the chambered round. Unacceptable for a duty weapon.

I own a lot of PMAGs, both gen2 and gen3. I don’t want to have to modify magazines. I don’t want a particular AR that will only function with selective magazines. I don’t want a duty weapon that can’t be relied upon to use magazines that another officer may have.

This is why I am selling off the lower. And this is why I am disappointed with my personal experience with BCM. Especially after two trips to the factory, only to be told not to use anything but mil spec aluminum magazines.

I have found an acquaintance willing to buy the lower, with full disclosure of the issues. He won’t be using it as a duty weapon or for HD.

I appreciate all the feedback from the LMT users. I was set to buy an LMT defender lower, but found a deal on a Colt 6920 OEM-1. And a friend who wants to buy the NIB 6920 upper.

20

These Gen3 mags seem to be causing a lot of comparability problems with lowers. I too have the same problem with one of my lowers. I contacted Magpul and they sent me the latest batch of magazines, but that still didn’t correct the issue. The lower works perfectly with mil-spec mags and previous generation pmags. Since then, I have shifted my supply of magazines over to NHMTG magazines since they perform flawlessly in every rifle I own.

I understand your frustration, It sucks having a rifle that you can’t trust with every magazine you own, but I think this may be a magazine issue.

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