M3 PMAGs won't lock in to lower

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[ARCHIVED THREAD] - M3 PMAGs won't lock in to lower (Page 1 of 2)

Posted: 12/11/2016 1:05:37 AM EDT

I think it's because of the over insertion tab. USGI and M2 PMAGs lock in fine. Does this mean the lower is out of spec or is it nothing to worry about?

Posted: 12/11/2016 1:38:07 AM EDT

[#1]

Quoted:
I think it's because of the over insertion tab. USGI and M2 PMAGs lock in fine. Does this mean the lower is out of spec or is it nothing to worry about?

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I made a thread about this a couple of weeks ago, I've got a billet lower, Aero M4 upper and Aero mil-spec bolt carrier, mine takes gorilla strength to lock in a gen 3 Pmag, USGIs are a little better but still way more force than any other AR I've owned. Tried a forged lower with the same result, don't know what the problem is, took it to a WECSOG smith who thought it was hard but "normal", but I've owned enough ARs to know it's not.

I neck-bearded out my other stuff while prices were high so I don't have another upper or carrier to compare.

Sorry I don't have anything useful to add, just posted to let you know someone else may be having a similar problem, I've got more parts coming so hopefully I'll find a solution, and maybe it'll benefit us both.

Posted: 12/11/2016 2:55:30 AM EDT

[#2]

M3 Pmags take a little extra "umph" to seat in both of my PSA lowers while M2, USGI and Lancer mags seat easily. M3's won't seat at all in my neighbor's Anderson lower but everything else does without a problem. The over insertion tab on the M3 appears to be causing the issue.

Posted: 12/11/2016 3:20:38 AM EDT

[#3]

You need to pop them hard to get them to seat, it has been floating around the .net for a while now that they don't lock well.

Posted: 12/11/2016 7:52:24 AM EDT

[#4]

Quoted:
I think it's because of the over insertion tab. USGI and M2 PMAGs lock in fine. Does this mean the lower is out of spec or is it nothing to worry about?

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The AR-15/M16 was not designed to work with Pmags. If USGI magazines (you know, the magazines that were originally and still are intended to work with the platform) work fine, then nothing is out of spec.

Posted: 12/11/2016 9:50:14 AM EDT

[#5]

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The AR-15/M16 was not designed to work with Pmags. If USGI magazines (you know, the magazines that were originally and still are intended to work with the platform) work fine, then nothing is out of spec.

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While the ar was not designed to work with pmags, pmags were designed to work with in spec ar's. Magpul says they will function at either end of the tolerance spectrum. The USGI is more forgiving to out of spec loweres, but I would argue that if it doesn't work with a pmag it is out of spec. The pmags are a consistent size and lowers very because of things like tool wear.

Posted: 12/11/2016 10:15:26 AM EDT

[#6]

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Quoted:
While the ar was not designed to work with pmags, pmags were designed to work with in spec ar's. Magpul says they will function at either end of the tolerance spectrum. The USGI is more forgiving to out of spec loweres, but I would argue that if it doesn't work with a pmag it is out of spec. The pmags are a consistent size and lowers very because of things like tool wear.

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Quoted:

Quoted:

The AR-15/M16 was not designed to work with Pmags. If USGI magazines (you know, the magazines that were originally and still are intended to work with the platform) work fine, then nothing is out of spec.

While the ar was not designed to work with pmags, pmags were designed to work with in spec ar's. Magpul says they will function at either end of the tolerance spectrum. The USGI is more forgiving to out of spec loweres, but I would argue that if it doesn't work with a pmag it is out of spec. The pmags are a consistent size and lowers very because of things like tool wear.

The magazines need to fit the rifle. Not the other way around. M3 PMAGS feature decreased compatibility.

Posted: 12/11/2016 10:52:03 AM EDT

[#7]

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The magazines need to fit the rifle. Not the other way around. M3 PMAGS feature decreased compatibility.

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The Pmag fits any rifle that is to USGI spec, how can they be expected to fit ones out of spec? Or, more appropriately, ones built to a different spec. They feature increased reliability rifles that are in spec. A buyer makes their choices. You want a nice looking billet lower? You may have to give up ability to use a m3 pmag with it's over insertion stop. You want to pay 50 bucks for a lower? You may run into manufactures that run their machines longer and exceed when you normally would replace mills and bits, with the lowers drifting out of spec as they try and save money on replacement costs.

Posted: 12/11/2016 11:16:23 AM EDT

[#8]

OP and Mike_Deezy,

Have either of you tried inserting mags with the upper taken off the lower? I have seen a few mags that were the wrong shape/size at the top and would scrape on the inside of the upper. They fit the lower fine and would insert and drop free normally without the upper. When I put the upper back on they were very difficult to lock in and would not drop free. A bit of work with a small file on the outside of the very upper edge of the feed lips made the mags fit much better. These were stainless mags and if you looked inside the upper you could see marks where they were hitting.

Posted: 12/11/2016 11:21:19 AM EDT

[#9]

There are numerous threads about canted rounds in the M3 magazines. Magpul says it's a non issue, but it happens to all of my M3 magazines and they changed the Sand mags to mitigate the issue.

M3 problems

Posted: 12/11/2016 11:24:47 AM EDT

[#10]

I had a BCM lower that wouldn't let Gen3 PMags lock in. BCM ignored me completely when I asked about it. I ended up slightly filing the lower, had to take off barely any material and now they lock in fine. A little alumablack and its looks brand new. I posted pictures of it in an old thread and people went ape shit that I dare to touch a BCM lower with a file. To me it was worth it, I have about 20-30 gen3's and I didn't want to be in a situation where some mags don't work with any particular gun.

Posted: 12/11/2016 12:03:51 PM EDT

[#11]

Topic Moved

Posted: 12/11/2016 3:41:04 PM EDT

[#12]

Quote History

Quoted:
While the ar was not designed to work with pmags, pmags were designed to work with in spec ar's.

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And that rifle is in spec if it works with the magazines it's designed to work with....USGI aluminum. If a Pmag isn't compatible with a rifle that works with its intended magazines, the Pmag is the problem. Why do you think they have multiple generations? How long has the USGI magazine remained untouched?

Posted: 12/11/2016 3:47:17 PM EDT

[#13]

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There are numerous threads about canted rounds in the M3 magazines. Magpul says it's a non issue, but it happens to all of my M3 magazines and they changed the Sand mags to mitigate the issue.

M3 problems

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I am aware of this issue but this is not the problem. The over insertion tab is contacting the lower before the mag can lock in.

Posted: 12/11/2016 4:53:06 PM EDT

[#14]

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And that rifle is in spec if it works with the magazines it's designed to work with....USGI aluminum. If a Pmag isn't compatible with a rifle that works with its intended magazines, the Pmag is the problem. Why do you think they have multiple generations? How long has the USGI magazine remained untouched?

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I don't have a stake in it. There has been more generations of usgi then pmag, not to mention followers. All I am saying is you have a choice. An in spec lower will work with a usgi or the superior to usgi (in lots of peoples opinion and by testing). You can go with an out of spec lower that might have extra features or some other benefit that the pmag doesn't work with. Although a pmag will work with most of them. The benefit of the usgi is that it will work with anything. You just can't blame the pmag when it doesn't work in your lower. Pmags are molded not individually machined or broached. I am guessing they have a lot less variance dimensionally then an ar. You can't expect it to work in ar's that are not to spec.

Posted: 12/11/2016 6:14:32 PM EDT

[#15]

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I don't have a stake in it. There has been more generations of usgi then pmag, not to mention followers. All I am saying is you have a choice. An in spec lower will work with a usgi or the superior to usgi (in lots of peoples opinion and by testing). You can go with an out of spec lower that might have extra features or some other benefit that the pmag doesn't work with. Although a pmag will work with most of them. The benefit of the usgi is that it will work with anything. You just can't blame the pmag when it doesn't work in your lower. Pmags are molded not individually machined or broached. I am guessing they have a lot less variance dimensionally then an ar. You can't expect it to work in ar's that are not to spec.

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What variations have there been in the body of an aluminum USGI mag since the 1960's? How have they changed? And polymer will swell long before aluminum. BTW, as far as your "superior" comment, I decided to read a little in that "high round count AR" thread by Henderson Defense. Somewhere in there, he stated that USGI magazines have been more reliable than Pmags.

Posted: 12/12/2016 6:01:40 PM EDT

[#16]

I have one P mag that does that same thing. I really have to give it a little extra push to make sure it seats in there.

Posted: 12/12/2016 6:13:05 PM EDT

[#17]

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What variations have there been in the body of an aluminum USGI mag since the 1960's? How have they changed? And polymer will swell long before aluminum. BTW, as far as your "superior" comment, I decided to read a little in that "high round count AR" thread by Henderson Defense. Somewhere in there, he stated that USGI magazines have been more reliable than Pmags.

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Link

Also Magpul has done a lot of innovation with magazines and the gen 3 is a very good magazine.

If PMags won't fit your lower but USGI do it's because your lower is at the extremes of the specs. I've had a few over the years and wound up selling those lowers. All of mine I have now will seat any generation of PMag.

Posted: 12/20/2016 12:44:20 PM EDT

[#18]

Quoted:

And that rifle is in spec if it works with the magazines it's designed to work with....USGI aluminum. If a Pmag isn't compatible with a rifle that works with its intended magazines, the Pmag is the problem. Why do you think they have multiple generations? How long has the USGI magazine remained untouched?

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That's not how specifications work. They don't give machine shops a print that says "this dimension has to be enough to let this batch of mags we gave you drop free." There's an actual dimension the magwell is supposed to be. It could be that per "spec" the mag well is designed with a .025 inch minimum gap on each side of an in spec USGI mag. That means that the well could still be .020 inches too narrow per side and still fit a USGI mag. The lower is out of spec, but the USGI mags still fit.

It's possible pmags are designed to fit with a .015 inch gap to create a more snug fit. They should still fit all in spec lowers. It's possible that a lower could be too narrow for pmags while still allowing USGI mags. It could be out of spec with this situation, and still fit USGI mags. Note these numbers are totally made up, but I used them to illustrate the point. If I had to guess, they design them tighter as thermal expansion isn't as much of a factor for plastic as it is for aluminum, so they can bring the gaps down more than a comparable aluminum mag that may change dimensions due to temperature or minor dings from handling.

Basically, a lower can be out of spec and still fit some mags and not others. Tolerances can also play a role as well if something is slightly out of spec. I had a lower from Aero recently that only dropped free with half of my pmags. It was returned for service and when I got it back it was 100%. My other lower fits them all fine.

Posted: 12/20/2016 1:13:43 PM EDT

[#19]

It's the lower.

In my experience LMT and Colt machine the best lowers and are always compatible with the Gen M3 Pmags.

PSA sells super cheap aluminum mags for the 'Just as good as' crowd.

Posted: 12/20/2016 6:33:51 PM EDT

[#20]

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It's the lower.

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If everything else works fine but a M3 PMAG, it's the mag. M3 mags don't drop free from my Daniel Defense rifles. Everything else does. I guess I bought substandard rifles?

Posted: 12/20/2016 6:42:00 PM EDT

[#21]

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If everything else works fine but a M3 PMAG, it's the mag. M3 mags don't drop free from my Daniel Defense rifles. Everything else does. I guess I bought substandard rifles?

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It's the lower.

If everything else works fine but a M3 PMAG, it's the mag. M3 mags don't drop free from my Daniel Defense rifles. Everything else does. I guess I bought substandard rifles?

They are on the extreme end of the spec for the magwell, as has been repeatedly said.

Posted: 12/20/2016 7:16:15 PM EDT

[#22]

My cousin has a Troy rifle....
gen 1&2 Pmags will not drop free. Gen3 Pmags will , as will GI.
Supposedly, his lower is machined to tighter tolerances.?? Or so says he.All mags will seat, though some are stiff.

My cheapo Anderson lowers take all Gen PMAGS and USGI with zero issues. Thank God I am a cheap bastard.

Posted: 12/21/2016 12:21:53 AM EDT

[#23]

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If everything else works fine but a M3 PMAG, it's the mag. M3 mags don't drop free from my Daniel Defense rifles. Everything else does. I guess I bought substandard rifles?

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The Gen M3 is compatible with all mil-spec M16/M4 and M27 magwells and is a USMC issued magazine. It is compatible enough that they chose it over their own magazine that they designed especially for their ammo and rifles. I'm still betting on your lower.

Posted: 12/25/2016 11:31:03 AM EDT

[#24]

My colt le6920 won't take gen m3 pmags and that is as mill spec as ar's get. Magpul has a problem.

Posted: 12/25/2016 1:29:17 PM EDT

[#25]

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If everything else works fine but a M3 PMAG, it's the mag. M3 mags don't drop free from my Daniel Defense rifles. Everything else does. I guess I bought substandard rifles?

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Clearly one of the few who understands.

Posted: 12/25/2016 2:26:22 PM EDT

[#26]

I had a lower that was tight fitting m3 pmags and hex mags.
Turned out the tabs were hitting the front side of the aftermarket trigger guard.
I feathered down the trigger guard with a file and they seat fine now.

Posted: 12/25/2016 6:04:41 PM EDT

[#27]

I mean the adoption by the USMC pretty much resolves the whole issue. Pmags fit in spec lowers. It doesn't fit your lower your lower is out of spec. That isn't a bad thing. Just like bcm charging handles or midlength gas is not in spec. Manufactures make their parks to their own specs which may or not coincide with mil spec.

By definition they are mil-spec.

Posted: 12/25/2016 7:53:37 PM EDT

[#28]

It seems like people had little to no problems with the gen 1 and 2's, that was when Magpul had the Emag going strong. Supposedly (from what Ive read) the new M3's crossed over into the Emag specs to try to cover more 556 platforms.

Posted: 12/25/2016 11:07:25 PM EDT

[#29]

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The Gen M3 is compatible with all mil-spec M16/M4 and M27 magwells and is a USMC issued magazine. It is compatible enough that they chose it over their own magazine that they designed especially for their ammo and rifles. I'm still betting on your lower.

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Both rifles, both DD, don't drop M3s. I am not the only one with a DD who reports this. Guy in this thread has a Colt that won't take them either. Everything else from USGI to Lancer works fine.

I would bet the other way.

Posted: 12/26/2016 12:12:12 AM EDT

[#30]

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Both rifles, both DD, don't drop M3s. I am not the only one with a DD who reports this. Guy in this thread has a Colt that won't take them either. Everything else from USGI to Lancer works fine.

I would bet the other way.

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I've put hundreds of Gen M3s in numerous Colt and LMT lowers, never had a problem. The USMC has been using and testing the Gen M3 for over two years and they work better than anything they can afford to buy.

Don't know what to say about your DD lower other than find some mags that work in it.

Posted: 12/27/2016 1:56:00 AM EDT

[#31]

over insertion tab, a fix for people who need to stop taking so many steroids... wtf are you doing when you insert the mag.

I have a bunch of STANAG compatible guns, I don't want AR-15 only mags and then supposedly not all AR-15s.

Posted: 2/26/2017 8:25:34 PM EDT

[#32]

I have a Colt LE6920 and all five Gen M3 PMAGS that I bought didn't work. They either didn't lock up or didn't load the first round when I released the bolt. I sold them and bought more GEN 2's. They have never failed me.

Posted: 2/26/2017 8:50:00 PM EDT

[#33]

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Clearly one of the few who understands.

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If everything else works fine but a M3 PMAG, it's the mag. M3 mags don't drop free from my Daniel Defense rifles. Everything else does. I guess I bought substandard rifles?

Clearly one of the few who understands.

If I understand it right, the M3 was redesigned to accommodate the new feed angle needed to feed the M855a1 ammo due to a combo of conventional mags and the hardened tip causing premature throat erosion. The M3 has new feed lip angles and I believe USGI mags are being redisgined as well. As far as the overinsertion tab stuff, I refuse to own M3's as gen 2 and USGI work great in everything I have.

Posted: 2/27/2017 12:35:55 AM EDT

[#34]

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over insertion tab, a fix for people who need to stop taking so many steroids... wtf are you doing when you insert the mag.

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I believe it's also intended to help absorb the impact when a rifle is dropped on the magazine. I think that's part of what contributes to M3s surviving drops better than M2s (at least in the video tests I've seen).

Posted: 3/23/2017 9:13:26 PM EDT

[#35]

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I mean the adoption by the USMC pretty much resolves the whole issue. Pmags fit in spec lowers. It doesn't fit your lower your lower is out of spec. That isn't a bad thing. Just like bcm charging handles or midlength gas is not in spec. Manufactures make their parks to their own specs which may or not coincide with mil spec.

By definition they are mil-spec.

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Tons of shit bought by the military doesn't fit together. Just because the military buys two things that are supposed to fit together and that are designed to fit together doesn't mean they will fit together.

Posted: 3/24/2017 2:09:47 AM EDT

[#36]

Also just because the USMC is buying contracted PMAGs, doesn't mean you're buying the exact same PMAGs they receive. I'm not saying you aren't; I'm just saying it's possible. It wouldn't be the first time a GI contractor sold rejects to the civilian market, or didn't use the newest improved molds for their commercial production.

All tolerances stack. Any deviation increases the variance.

Posted: 3/24/2017 10:27:05 AM EDT

[#37]

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Tons of shit bought by the military doesn't fit together. Just because the military buys two things that are supposed to fit together and that are designed to fit together doesn't mean they will fit together.

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It is as simple as this. If your lower adherers to the TDP, m3 mags work. There haven't been any problems with USMC adoption.

Posted: 3/25/2017 2:39:51 AM EDT

[#38]

I was sad to find out that all three magwell adapters on my Lancer L15 lower would not work with with gen3 Pmags.

Posted: 3/26/2017 5:36:54 PM EDT

[#39]

I think the M3 roll out has shown a lot of lower manufacturers are slightly out of spec, either just off enough which never really mattered enough, or they made lowers with nice custom features which placed the bottom of the mag well out of true spec.

Somewhere I read Magpul gave a quick list of big name lower makers which did little changes to ensure the magwell - trigger guard area was in GI spec.

Posted: 3/27/2017 4:11:13 PM EDT

[#40]

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I think the M3 roll out has shown a lot of lower manufacturers are slightly out of spec, either just off enough which never really mattered enough, or they made lowers with nice custom features which placed the bottom of the mag well out of true spec.

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Not following your logic. Is the M3 more in spec than the M1 or M2?? I assumed each aftermarket brand stuck to one set of specifications regarding the dimensions that let it fit into the lower.

Posted: 3/27/2017 4:31:00 PM EDT

[#41]

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Not following your logic. Is the M3 more in spec than the M1 or M2?? I assumed each aftermarket brand stuck to one set of specifications regarding the dimensions that let it fit into the lower.

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The M3 has has the over insertion tab, if a lower is 'too big/long' in the magwell - trigger guard areas it won't go in. The M1 & M2 didn't have the tab.

Also, the M3's body meets the skinnier NATO spec, the M1 & M2 were designed a little larger than NATO spec to fill the magwell of the AR, M4, M16 series.

Posted: 3/28/2017 10:59:13 PM EDT

[#42]

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The M3 has has the over insertion tab, if a lower is 'too big/long' in the magwell - trigger guard areas it won't go in. The M1 & M2 didn't have the tab.

Also, the M3's body meets the skinnier NATO spec, the M1 & M2 were designed a little larger than NATO spec to fill the magwell of the AR, M4, M16 series.

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I (and I assume many others) always thought they were all built to NATO specs. Back in the day when people would complain the mags didn't drop free the mantra always was "your lower is out of spec". I don't pay too much attention to the specifications of aftermarket parts but I thought I remember the claim from the get go that they were built to government specifications.

Posted: 4/22/2017 12:59:18 AM EDT

[#43]

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I had a BCM lower that wouldn't let Gen3 PMags lock in. BCM ignored me completely when I asked about it. I ended up slightly filing the lower, had to take off barely any material and now they lock in fine. A little alumablack and its looks brand new. I posted pictures of it in an old thread and people went ape shit that I dare to touch a BCM lower with a file. To me it was worth it, I have about 20-30 gen3's and I didn't want to be in a situation where some mags don't work with any particular gun.

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Don't feel bad I had to do the same thing on my KAC SR-15 lower to get my Gen3 pmags to fit.

Sorry I have 150 of them and they worked fine in all my lowers but the KAC one.

It was a easy fix

Posted: 4/24/2017 10:10:32 PM EDT

[#44]

I just scored two of the new ~~MCT~~ Sand M3 mags off the EE... I will try them in my LMT and BCM lower and report back... not a big deal if they don't... I just wanted to score a few of them mags to see what all the fuss is about..

Posted: 4/26/2017 10:08:06 AM EDT

[#45]

The lower is slightly out of spec. Before the over insertion tab came along, a little extra length in the magwell never mattered, and producers could vary on dimensions or make customish magwells without issue. Now it matters.

Magpul has stated some manufacturers have had to get their magwells back in spec to meet the public's expectation the M3 mag should fit.

Posted: 4/27/2017 6:40:05 PM EDT

[#46]

Got my two M3 MCT mags today
both fit and drop free in both my BCM and LMT lower with no issues....

And as to the color....too light for my tastes.... Krylon, once again is my friend.

Posted: 5/3/2017 7:59:21 PM EDT

[#47]

they work fine in my anderson lower but are tight to lock in in my spikes unit. it works in the spikes but i wont use them in the event i *need* to use them

Posted: 5/11/2017 5:03:58 PM EDT

[#48]

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Don't feel bad I had to do the same thing on my KAC SR-15 lower to get my Gen3 pmags to fit.

Sorry I have 150 of them and they worked fine in all my lowers but the KAC one.

It was a easy fix

https://www.AR15.Com/media/mediaFiles/20856/IMG-1065-183266.jpg

https://www.AR15.Com/media/mediaFiles/20856/IMG-1067-183265.jpg

https://www.AR15.Com/media/mediaFiles/20856/IMG-1066-183268.jpg

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I had a BCM lower that wouldn't let Gen3 PMags lock in. BCM ignored me completely when I asked about it. I ended up slightly filing the lower, had to take off barely any material and now they lock in fine. A little alumablack and its looks brand new. I posted pictures of it in an old thread and people went ape shit that I dare to touch a BCM lower with a file. To me it was worth it, I have about 20-30 gen3's and I didn't want to be in a situation where some mags don't work with any particular gun.

Don't feel bad I had to do the same thing on my KAC SR-15 lower to get my Gen3 pmags to fit.

Sorry I have 150 of them and they worked fine in all my lowers but the KAC one.

It was a easy fix

https://www.AR15.Com/media/mediaFiles/20856/IMG-1065-183266.jpg

https://www.AR15.Com/media/mediaFiles/20856/IMG-1067-183265.jpg

https://www.AR15.Com/media/mediaFiles/20856/IMG-1066-183268.jpg

I took a close look at my PSA lower and noticed that one side of the magwell was noticeably higher than the other. After a little filing the M3's are working great. Who doesn't love filing on an SBR lower right?