Now that I look more closely at the rifle, Only the inner portion of the rail system could come down and over the lipped portion of the upper receiver.

I decided to try an replicate the problem with my gun which is a very early ACR being under 300. Although this is very subjective, I used what I considered to be normal low stress mag insertions with the a full 30rnd Pmag and a USGI mag, no issues. I did the same thing with alot more force, causing slight discomfort in the palm of my hand, and could not get the mag to over insert. I tired it one more time; I hit the magazine very very hard once inserted, much harder then you would ever have to hit a magazine, causing noticeable discomfort in my hand. With both the Pmag and the USGI mag the first round was ejected from the magazine, with slight over insertion with the USGI mag. I released the bolt button, and the bolt went into battery correctly with the round.

I tired this a couple more times, and could not replicate the problem again, but I noticed my whole hand was holding the pistol grip due to the force I was hitting the mag with, which is not normal. Generally my finger is resting in the area of protective lip of the mag release; as it helps me stabilize the rifle better when reloading. I put my trigger finger where it is normally, slightly turned over the rifle as I would to reload it slammed the magazine in place. Sure enough the mag catch was in the disengaged position, as it seemed I was also applying unintended pressure on the mag release. I turned the rifle over and the first round was partially disengage from the magazine, just as before.

Now I haven't seen Tokarev's videos so I am not sure how he was inserting the mags, but I generally insert the mag firmly, then give a a nudge further and a pull to make sure it is seated fully. Doing this I couldn't get the mag to over insert, even slamming the mag relatively hard, hard enough that my hand now hurts. Based of what my rifle is doing it seems if you insert the magazine with a very swift hard initial insert, not giving the mag catch enough time to reset; it may over insert without any pressure on the mag release.

If I do that, I can get the first round pop out of the mag and the rifle, however unless I hold the mag in the over inserted position, I can always let the bolt release go and it will send the round in to battery just fine.

This being said, It would be nice if there was a means to prevent over insertion, but it took alot of force, which is not needed in magazine changes to get the magazine to over insert. Before this thread came back to life this was the first I had ever heard of this issue arising. I would personally be interested in a means to alleviate this from happening, just to cover all bases, Though I had to go to some effort to get my rifle to do it, far oustide of what I consider normal magazine changes.

 

 

 

Well, Gen 3 PMAG magazines don't appear to be the answer. They don't spit rounds but the over-insertion tab on the spine of the mag is too low. The mag catch takes all the force and is the only thing keeping the mag from going too far into the mag well. This mag has only been used a few times and now sticks up beyond the catch since part of the plastic has been broken off. Pushing down on the bolt release pushes the mag down but it wall fall out of the rifle about half the time without being caught by the mag catch.

 

Well, Gen 3 PMAG magazines don't appear to be the answer. They don't spit rounds but the over-insertion tab on the spine of the mag is too low. The mag catch takes all the force and is the only thing keeping the mag from going too far into the mag well. This mag has only been used a few times and now sticks up beyond the catch since part of the plastic has been broken off. Pushing down on the bolt release pushes the mag down but it wall fall out of the rifle about half the time without being caught by the mag catch.

FWIW, I too have noticed similar damage to polymer mags (PMAG and Lancer) in the catch area. This damage occurs if the magazine is slammed up into the lower receiver. I've looked at the lower and how the magazine interacts with it, and the protruding latch is the only thing stopping the mag from moving upwards any further. If the mag catch were to go past the latch, then the last thing to stop the mag's upward travel is the bolt release mechanism. This isn't a problem if the bolt is already in battery as the carrier itself would prevent the magazine from going any further into the upper receiver. If the bolt is locked back and a magazine is slammed upwards, then the mag latch (or under extreme circumstances, the bolt release) will stop the upward movement but as a result can sometimes cause a round to eject from the magazine.

With regards to a round being released from the magazine by rapid, forceful insertion, I can see where in a high-stress combat environment that this may become an issue. This becomes especially evident if the operator does not realize a round is floating loose in the breech then proceeds to release the bolt.

I do not think you have anything wrong with your lower per se - this is simply a design oversight that relies on the magazine catch to prevent over insertion. I concede it would have been better if Bushmaster had implemented a better solution like rails that would prevent over insertion. It still would not address the issue of a round being ejected if the operator was overly ambitious in mag changes. I've seen the same thing happen with the AR platform. With that said, I no longer use polymer magazines with the ACR and instead rely on USGI steel or aluminum magazines with good followers.

P.S. If it helps you, I can take calipers and measure the magazine well from side to side and front to back. Not a very scientific approach but it might give you an idea if something is grossly out of whack with your lower. I saw one of your videos where you tried 3 magazines and the amount of rounds ejecting from insertion is disconcerting. I have not experienced that many myself.

 

I'm starting to think you have something wrong with your rifle. Nobody else has these problems. It's kinda interesting. If bushmaster would listen they would probably fix it.

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Know anyone who's got a spare lower I can barrow? That way I can see if it's something unique to my lower specifically.

 

I actually had this happen at the range with a Lancer L5AWM...but I was pretty rough with the insertion. (twss)

 

Your most likely going to need precision tools to measure the components of each lower. Yes something could be off by that much. I hate to say this but you may have gotten a lemon, I'd contact BM about it and make sure they watch the video.

 

The ease with which that happens is startling, as I said before to get my rifle to do anything similar I had to literally had to abuse it and myself. If you have a set of calipers, I have alot of measurement from my lower that could be compared. However injected molded parts have alot of variance to them. Regardless, I would say a new lower is in order from BM.

Edit, thank you for reposting the videos.

 

I pulled them initially because I wanted Bushmaster to respond and didn't want my videos potentially hurting sales. I emailed the videos to Bushmaster shortly after filming and I sent them again earlier in the week. I've still heard nothing.

In frustration I emailed Remington with the videos and got a response within a couple days. Too bad the only advice Remington has is to email Bushmaster!

 

I had hoped that the new Gen3 PMAG magazines would be the "answer" to my troubles with the ACR. Initially the mags showed a bunch of promise. Now, after a few reloading drills, I see the block underneath the magazine catch slot has chipped. Now this magazine easily jumps past the mag catch and gets pushed up too far into the mag well and is stopped by the bolt catch tab. Pushing down the bolt catch lever will push the mag back down into proper position but it will fall beyond the mag catch about half the time and drop clear out of the rifle without feeding a round.

Also note, when using the magazine as a monopod, the bolt carrier is hitting the back corners of the feed lips.

 

Not for nothing, but I don't give a dam what any one says you should never (use the magazine as a monopod) and rest the weapon on the magazine. Your putting undo pressure on and interfering with the device that is responsible for feeding ammo and that is never a good thing. Use your weak hand to do that.

I'm convinced your lower is FUBAR. Put pressure on shrubmaster for a replacement.

 

I sent the photos of the Gen3 PMAG to one of the customer service guys from Magpul and he told me that they didn't see that kind of chip even after dropping a loaded rifle from a height of eight feet.

Ideally I need to find a new or recent production ACR and see how my mags fit in that mag well.

 

You need to find a local member so you can check this out. Or just go to a dealer that has one in stock to compare, just play dumb.

 

If it's the notch in the magazines doing it for him, maybe it's just the mag catch?

 

Remington needs to design and release a new Remington ACR with the upper receiver redesigned to prevent over-insertion of the magazines. Much like an AR upper. Either that or Marvin needs to release a new lower receiver designed to use the over-insertion tab on the new M3 PMAGs. Either way, I'm in for whatever comes to market first.

Oh, and I still need an AK lower receiver to use with my 7.62x39 kit. It runs great but the added reliability of the AK magazines would be a nice addition to the rifle.

 

Tabs cannot be added to the lower, The magazine passes through it into the upper receiver quite far, just shy of the ejection port. Material or a modified bolt bearing surface would have to be implemented in the upper.

 

I'm thinking a tapered "sleeve" that goes in from the top into the mag well. It would be (very) thin on top and the sides except for some 'ribs' that would act as stops for magazine insertion from the bottom. Act as a sort of collar for the magazine.

I can't even duplicate this though so mostly idle speculation. Imagine a combination of mags and something with his mag catch and/or the tolerances in the lower itself. Since the firearm is the upper, I'd be more loath to do anything to that, though Remington could certainly put a change in future iterations.

 

I personally think this is not a big enough issue to address. It would be nice if there was an easy fix, but a complete design change is not worth doing.

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Tabs cannot be added to the lower, The magazine passes through it into the upper receiver quite far, just shy of the ejection port. Material or a modified bolt bearing surface would have to be implemented in the upper.

Marvin could easily add tabs to his lower, as it has not been released yet. Over-insertion tabs or stops, if you prefer, could easily be made into that lower. I feel that a better fix would be a new upper from Remington that uses a new AR type bearing surface. Remington could easily modify the upper but probably won't do this. Honestly, in addition to a new improved Remington upper, I'd like to see one convertible lower manufactured that would use all the different magazines: AK-47, AR15, AK-74 and the new 6.8 mags. This would truely make the ACR modular.

As I go forward with the ACR, I will be focusing more on streamlining caliber choices for my use. The 6.5 Grendel/264LBC is a must have caliber for me. This caliber makes the ACR a truely do-everything rifle. Shooting the 7.62x39 and 5.45x39 Russian calibers would be nice in a survival situation but could be replaced with the .300 Blackout ballistically. The ammo would be costly and supplies iffy. Massive tradeoff there! The 5.56 NATO is also a must have caliber but a 1/7" twist barrel is needed.

 

A modified lower will not solve this issue. I had, and currently have my rifle on my lap with a magazine in the well. The ACR upper extends much father down then an AR, and therefore the lower cannot effect any real change, as the problem area is 5/8" above the top of the lower. A sleeve may be able to be inserted which could alleviate this problem.

Since the ACR bearing surface are two C channel steel rails which bolt in, this could be an easy fix. The non ejection port side could be modified to be two prongs, which could skirt around the raised portion of the upper which is beneath the steel rail. This could provide over insertion protection.

This being said, no one else has had this problem, and we're still exactly sure what is truly causing the problem. Is is mag latch out of spec? or is the injection molded lower out of spec, and therefore the mag latch is out of spec as well. We need to narrow down the problem. This will allow us or Remington to provide the best solution.

On a separate note, what changes have been made to the Remington upper?

 

Only change in the Remmy upper is the riveted latch for the folding charging handle IIRC.

 

that and the smoother rounded rails with the engraving marks between them

 

I a while back I tried slamming a mag into my rifle with the carrier locked to the rear and wasn't able to get it to pop out any rounds with a few different mags. I've heard of a couple of other people having this issue though.

 

Got any threads or anything where other owners have commented about ejecting rounds? In one of my conversations with Bushmaster Customer Service, I was told that nobody has ever had a problem with this type of stuff before. It would be nice to be able to provide additional proof.

 

I posted on arfcom, but if I give my mag a real "where's mah money, bitch?" slap, I can get a round to pop out of the mag, so it's not one guy making it up.

 

If you slap the mag out of the gun you can have rounds pop out as well

 

True but not with the limited amount of force I used making the videos. I believe the sudden stop of the mag body coupled with flexible plastic and no internal feed lip supports allows the inertia of the ammo stack to force a round out of the mag.
I find it interesting that the IWI Tavor does have internal feed lip supports built into the top of the mag well.

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Have you tried the m3 pmags?

 

Yes. Gen3's have been made more compatible with more AR lowers so they're pretty sloppy in the ACR mag well. Shooting prone with a magazine as a monopod results in shaved plastic from the bolt carrier hitting the feed lips. Also, the Gen3's are more brittle so the over-insertion tab on the magazine will chip away in short order.

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