View Full Version : PMAGs not locking bolt open...figured out why
I've had random issue of my 30rd PMAGs not locking the bolt open on the last round. I was chalking it up to possibly the WOLF ammo just not always providing enough gas pressure until last weekend.
I was at the range and the first mag of the day didn't lock open, so I marked the mag. Went on to the next mag and it did lock open...same lot of wolf ammo. Then I loaded the first mag with some 5.56 and again it did not lock open.
When I got back to the table I compared this mag with the one that did lock open and the difference was immediately obvious....the follower was not coming up as far on the mag that did not lock open.
Didn't see anything blocking the movement so I pulled them apart and found two different follower designs, one with a shallower channel for the follower stop.
Pics:
Left is the one that did not lock open, right is the one that did.
http://farm7.static.flickr.com/6186/6138652339_15c9dea13b_b.jpg
http://farm7.static.flickr.com/6171/6138656687_5c85c9c99e_b.jpg
http://farm7.static.flickr.com/6061/6138654305_4b543df9a2_b.jpg
The mags that have the shallower stop channel do not always fail to lock the bolt open, but it happens often. When I got home I emptied all my mags and checked them. I have 12 standard 30rd PMAGs and one windowed. 6 of the standards and the windowed have this shallow channel follower.
All of the mags with the issue are marked M7 and M8, W2 for the windowed. The others are mostly M3 and M4, but there is one M8 that is OK. All of the mags appear to have been made in various months of 2009.
I've emailed MAGPUL but haven't gotten a reply yet.
Just thought I would post my findings for any others who might be having problems PMAGs not locking the bolt open...may want to have a look at the follower.
I found one thread from last year with a similar comparison, but the posters issues were related to FTF malfunctions. None of these mags have caused any malfunction other than failing to lock the bolt open.
Magpul is usually pretty good about this. You should hear something positive from them soon. Keep us posted.
O
I was having this exact same problem with all 6 of my PMAG's! I'd relegated them to range-only use and replaced them with L5's, but now I'll have to see if I can modify the followers. Nothing to lose, right?
Belmont31R
09-15-11, 01:31
Just contact Magpul.
Once I honestly posted a thread on TOS many years ago about how I knocked one off the top of my bed while playing with the wife. It fell about 5ft down onto our hard wood floor, and split down the back. They gave me two free mags no questions asked even though I broke it by knocking it off a bed post 5ft tall.
I am sure they will also want to take a look at them if they aren't already aware of an issue.
Like it or not when you are dealing with high volume stuff made on machines things happen. I would just PM the guy Dozer on here. If you want a resolution contact the guys direct not some 800 number.
billybob19606
09-15-11, 20:52
Are these things common after you use them awhile?
Magic_Salad0892
09-15-11, 21:27
Once I honestly posted a thread on TOS many years ago about how I knocked one off the top of my bed while playing with the wife. It fell about 5ft down onto our hard wood floor, and split down the back. They gave me two free mags no questions asked even though I broke it by knocking it off a bed post 5ft tall.
You guys call it ''playing''?...
billybob19606
09-15-11, 22:47
LOL! More "play" may equate in more free mags...
BufordTJustice
09-15-11, 23:29
You guys call it ''playing''?...
That's classic self-censorship. They must have kids. ;)
SSRacer,
Can you take a few shots of the magazine in the lower to see how much of the bolt catch engages the follower? We have seen issues with some bolt catches not being long enough to engage the follower. Thanks.
When I got back to the table I compared this mag with the one that did lock open and the difference was immediately obvious....the follower was not coming up as far on the mag that did not lock open.
I recon Dozer has already posted, and that you might as well be working out a solution.
But something intrigues me:
Did you see any markings on the followers?
For my untrained eyes they seem to be different molds/tooling.
Once I honestly posted a thread on TOS many years ago about how I knocked one off the top of my bed while playing with the wife. .
You guys call it ''playing''?...
Must not have had any kids. ;)
ApacheTactical
09-16-11, 15:11
Interesting Post. Thanks for the information that may save alot of us issues later.
I knocked one off the top of my bed while playing with the wife. It fell about 5ft down onto our hard wood floor, and split down the back.
Apparently PMAGs have uses the rest of us must not be aware of. 5 foot drop is pretty impressive as well.
(Yeah, I know. Now back to the actual topic...)
I've beat the snot out of my 30s and 20s, never had a single issue like this - always locked back every time. Multiple purchases spread out over years. I'll have to go back and compare them.
Thanks ssracer for posting the pics.
Magic_Salad0892
09-16-11, 15:58
Apparently PMAGs have uses the rest of us must not be aware of.
Can't say a PMAG has ever gotten me aroused....
Different strokes for different folks I guess.
Doc Safari
09-16-11, 16:42
SSRacer,
Can you take a few shots of the magazine in the lower to see how much of the bolt catch engages the follower? We have seen issues with some bolt catches not being long enough to engage the follower. Thanks.
Great idea. Minor variations in the mags might be pointing to something about the rifle instead.
SSRacer,
Can you take a few shots of the magazine in the lower to see how much of the bolt catch engages the follower? We have seen issues with some bolt catches not being long enough to engage the follower. Thanks.
Will do. Shooting tomorrow, once some of them are empty I'll get some shots with the upper off the rifle with both follower types.
FChen17213
09-17-11, 01:16
I am also interested in this bolt catch topic used with PMags. I have a well used rifle with well used PMags. Sometimes, the Pmags aren't locking the bolt back. If I put the used PMags with a newer rifle, the bolt locks open fine. If I use GI Mags or new PMags in the well used rifle, the bolt locks back. It's only when I use the well used rifle and well used PMags that the bolt fails to lock open. I notice a larger amount of fore/aft play in the bolt catch of the rifle. The mag followers are sometimes not catching the bolt catch and instead sliding past and then binding.
I'm guessing that in my situation, it is a combination of worn mags nad a worn rifle. Anyone else have this issue?
RogerinTPA
09-17-11, 06:57
I own about 100 of the older Pmags. I've had several where the bolt catch slips off the follower, down in to the gap of the mag body, causing the same issue.
The issue is intermittent with these mags. Used all six of the standard mags with this follower today at the range and only had the bolt fail to lock back once.
Belmont31R
09-17-11, 15:34
I am also interested in this bolt catch topic used with PMags. I have a well used rifle with well used PMags. Sometimes, the Pmags aren't locking the bolt back. If I put the used PMags with a newer rifle, the bolt locks open fine. If I use GI Mags or new PMags in the well used rifle, the bolt locks back. It's only when I use the well used rifle and well used PMags that the bolt fails to lock open. I notice a larger amount of fore/aft play in the bolt catch of the rifle. The mag followers are sometimes not catching the bolt catch and instead sliding past and then binding.
I'm guessing that in my situation, it is a combination of worn mags nad a worn rifle. Anyone else have this issue?
Try installing a new bolt catch (Colt). I standardized on them in all my AR's because they are usually correct length to catch the follower. Some other brands vary in size so much you can run into the issue. Not saying its guaranteed to work but there is quite a bit of geometry involved with how things are laid out and supposed to interact.
Fchen17213 the channel in which your bolt release sits in maybe worn or cut to wide, a thin small waster placed on the left side around the roll pin will straiten the release as it maybe slouched over do to excessive gap. You may be able to find a tiny washer or e clip at a hardware store. I done this on several out of spec Sharps Rifle Company lowers and they work great now.
Finally got around to getting some pictures. There is not much play at all in the bolt catch as far as wobble and it makes good contact with both followers. I wiggled and jiggled as much as the stop would move and there's no way it can slip off the follower. You can see that on the follower with the shallower stop channel that the front of the follower isn't coming up as far as the other.
From the front:
http://farm7.static.flickr.com/6169/6168169798_7b3bb05a38_b.jpg
Shallow channel follower
http://farm7.static.flickr.com/6152/6168167992_fe79d69bb9_b.jpg
Deep channel follower
http://farm7.static.flickr.com/6166/6168168894_aa0e5e1750_b.jpg
From the rear:
http://farm7.static.flickr.com/6173/6168170828_605dc11db2_b.jpg
Shallow channel follower
http://farm7.static.flickr.com/6171/6167636197_cf6ca8f331_b.jpg
Deep channel follower
http://farm7.static.flickr.com/6161/6167637409_3b95f25f3c_b.jpg
Is that a BAD lever? is it possible it could have anything to do with it? I've heard about them exerting a slight pressure, which in my mind would exacerbate any issue there might be. If this were my rifle I'd try removing that just to see what happened.
I'm just a 90% lurker ar noob though, so take anything I say with a grain of salt. I just wanted to throw that out there.
I've heard the same stories. But I played with it for a good half hour tonight and just don't see how it could possibly cause any issues. I just don't see how it has enough mass to it to cause any ill effects. I inserted the empty mag, pushed the follower down and let it rise back up, there was no hesitation of the mag catch to move. And when shooting my finger stays firmly on the trigger and I haven't been wearing gloves so there is no chance of me riding the bad lever.
Belmont31R
09-20-11, 22:45
Take that contraption off, install Colt bolt catch.
If you still have issues I will swap you lowers with something that works (minus that BAD contraption).
Next time I go out I will see if I can get one mag to fail consistently, like I said, this issue is intermittent. If I can get one to do it I will remove the BAD lever and try again, as that is an easy check. I'm not about to start blaming the lower and the LPK for the issue when I see no issues with them but can point out a distinct difference in follower design. The followers with the shallower channel would not be exerting as much force on the mag catch because they are not trying to push it up as far. I wish I had access to a force gauge to verify this.
I believe that Belmont's advice will be your best course of action. Replacing your current bolt catch with a Colt bolt catch will help alleviate any issues you have. Either way, feel free to call our customer service line to have your magazines replaced. I know you emailed them but considering the amount of email traffic they receive I would suggest you call instead.
I hope this helps.
I appreciate the advice. I'm just curious, how would the Colt bolt catch differ from the one currently on my rifle?
Colt is actually held to the TDP. The difference could be in the bar that makes contact with the follower or the width of the section that mounts into the lower. Any dimensional difference in any of the areas can potentially cause a problem. The worst we have seen is DPMS but without having your particular catch to compare to a Colt I could not say with certainty what the actual difference is.
a308garand
09-21-11, 21:48
What make is your receiver? It may be your receiver and not the magazines....
Parts manufactured at different times can have slight variations in size, so there is a + and - size that is considered to be within spec.
Colt rifles are held to a very tight standard, as are the other parts they put in their rifle. The parts all come together and are supposed to work together.
When you get a receiver from one maker, and parts from another, very slight manufacturing tollerances (the + and - sizes) can come into play and cause performance issues.
I have an early PWA receiver that either has the magazine well broached slightly forward from the bolt catch channel OR the bolt catch channel is slightly rearward from the magazine well.
That PWA receiver works 100% every day with USGI magazines, but when PMags hit the market, the bolt catch would fail to lock open. Another PWA receiver does not have this trouble and it works well with every magazine I have tried.
Upon digging into the measurements of the troubled receiver/bolt catch,,,the catch was just barely able to miss the rear of PMag followers. Looking at the PMag magazine body and also at the USGI magazine body, you will find the USGI body offers slightly more depth to allow the magazine follower to hit the bolt catch. The thinner USGI magazine body construction allows this.
I tried many bolt catches but none would measure long enough to be pushed reliably by the PMag magazine follower in my troubled receiver. I just bit the bullet and altered a Colt 9mm bolt catch to fit the receiver, allowing a longer "finger" to get pushed up by the follower.
So, in my case, it was only run USGI magazines in that rifle OR modify the bolt catch to ensure reliability. This is a training rifle, so no problem in leaning on this fix- if it fails, not sweat. It has been working well and showing no signs of failure for some time now.
Here is a link to TOS where I posted pictures regarding the fix for my rifle. http://www.ar15.com/forums/t_3_66/479984_Problem_bolt_catch__help_____Fixed_01_29_2010________.html
http://www.hunt101.com/data/500/ar04.jpg
The altered 9mm bolt catch.
My receiver is an Accurate Armory and the LPK came from them as well. There is no issue of the bolt catch missing the follower. I moved them both around as much as possible and there was no way for them to move far enough in opposite directions for the follower to slip past the catch.
The other PMAGS that I have run reliably 100% of the time. These run reliably most of the time.
capt_jerry
09-22-11, 06:00
Glad I checked this thread. It may solve my intermittent problems also.
Math is a powerful thing,
You can either have the polymer magazine weaker by being thin like the metal magazines in the back spine, or you have it where it is and just experience some market variances.
Short of making a pop out tail on the follower that would make it cost more..... you know how there is a stop on the front of the follower to bias the spring to bring up the tail to lift the bolt hold, well maybe this surface could be angled and push the follower to the rear of the magazine to get the best possible scenario for market compatability. Imagine all the AR's in the world, imagine what's out there.
Does this discovery shed any light on the fail to lock open problems associated with using an ambi bolt release
I've been using the same eight PMAGs for three years now and haven't had a single issue with any of them. Thousands of rounds, three deployments to Iraq, and they still work great with the occasional breakdown and wipe out.
I guess the bottom line is that that sure looks like more than "error" or "tolerance changes" through production. It would be interesting to see what Magpul has to say concerning the different heights of the shelf, besides just the bottom of the shelf channel being completely different. Is it possible that the shallow shelf follower was designed to mate with a particular body or vice versa? Have they answered you yet?
RioGrandeGreen
10-08-11, 23:33
Don't worry about having kids. Have a soundproof bedroom.!!!!!:D
TangoSauce
10-10-11, 20:16
You should call Magpul, I don't think I've ever gotten an email back from them before tbh. They'll have some information I'm sure. Customer service has always been pleasant.
TangoSauce
10-10-11, 20:54
Glad I checked this thread. It may solve my intermittent problems also.
I noticed is that when I switched over to a BCM Gunfighter it wouldn't lock with my Bushmaster BCG but did with a BCM BCG...something to keep in mind too.
copy that...never got an email back. Shot a little this weekend with some of these mags and had no issues. I have them numbered now so when it does happen I can verify exactly which mag(s) are doing it.
Pandamonium
10-12-11, 15:54
http://i658.photobucket.com/albums/uu306/PandamoniumNZ/AR15%20Photos/BoltLock.jpg
I have had a similar problem with some of my AR's.
In the picture above the circled part of the bolt release tends to touch on the back of the mag where the yellow arrow points.
The quick fix is to remove a small amount of plastic from the back of the mag (might not be that quick if you have a lot of mags):sarcastic: or from the front of the bolt release to give it a bit more clearance.
The other option is the colt 9mm bolt release as pictured below which doesn't have the extra "Tag" to rub on the back of the magazine.
http://i658.photobucket.com/albums/uu306/PandamoniumNZ/AR15%20Photos/Colt9mmBoltLock.jpg
Thanks to the guys for the use of their photo's.
I'll give that another look to see if the bolt catch is contacting the mag body, thanks
Was shooting yesterday; 30 Rd PMAGs' worked fine, 20 Rd PMAG failed to lock the bolt back. Will have to take a closer look next week when I am back.
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