I have some M1 and some M2 Pmags that will not go into a new to me AR-15.  It is a S&W M15 upper (need chrome lined barrels) and DPMS lower.  The friend I traded items to had three PMAG Moes from 2015 and they fit.  Then I tried sme PMAG M2 from 2018 and some fit well some were a pain to insert.  Then I tried a PMAG FDE from 2007 and it fit and dropped from but a PMAG Black from 2008 was a pain in the rear to insert in the magwell.  

Foilage M2 PMAGs, Sand, Black and FDE M3 PMAGs, Lancer, Troy, Hexmag series 1 (free), Brownells, DPMS, Center Industries, Colt, Labelle, D&H, Okay mags all insert fine and no issues with any of them.  

So basically I guess the DPMS magwell might just be on the tight side of tolerances?  Any remedy for this or just run it as is?

Also I know I should not have gotten this lower rifle combo but $425 was a good deal because it was a basically brand new M&P upper with a MPI bolt and the barrel was chrome lined and I could move this Rifle to my parents house for a plinker.  I just tried PMAGs while I had it in hand and it came with the that inserted fine but did not drop free but I have that same issue of dropping free from my Factory Colt 6920 so I was not concerned.


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Definitely no expert here, and perhaps because of that, I'd just go grab a new lower  


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Early gen pmags did not play well with some lowers.   Something about how the lowers had extra thickness on the rear of the mag opening to reduce mag jiggle and pmags were also made a bit thicker in the same place for that reason.   I had a smith lower that did not run gen 1 or 2 pmags.    It is fine with the later models.  

There may be a few old, old threads on it if you search   


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My few Pmag genM3 mags do not drop free from any lower I have tried, including Stag, Colt, DPMS.  Gen M2 and MOE mags drop fine.  I have had no issues inserting any mags in any lowers, just dropping.  I'm fine just buying new MOE mags.  Oh, wait.  I can't buy anymore useful Pmags in CT anyway.  Never mind.  

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Looks like it is just a few black ones have an issue inserting most do not, The colored pmags from m1 and m2 and my few black window mags no issues.  No only the m3s drop free but that is like that in a friends LMT.

I will just move those mags to training mags/range mags piles.

I had a gunsmith do some dimensions of the AR in question and it is in Spec just on the tighter side of tolerances and he said would pass if he still worked for brand X making USGI M4s.  

He did ask why I bought this because he could have gotten me a factory lower for $200 or less.  

I said most of my good rifles are out of state and I wanted something that I could use with my Comp M2 for around the house and it has a S&W factory upper (even the BCG is marked correctly) and I wanted a Chrome lined barrel in my upper.  



Now he is trying to sell me a KAC none ambi lower with a Geissle S3G trigger for $550.   

This topic came up in a recent Semper Paratus armorer class.

During the last several years, lowers have been made for brands (incl major brands) that this area of the magwell was a little generous. 

Couple that with the  anti-overinsertion tab on Gen 3 PMAGs, and you can get tolerance stacking that prevents the mag from full seating and locking in the magwell. 


A - grind on the most inexpensive part first

B - use high quality GI style mags

C - use Gen 2 pmags, they lack the anti-overinsertion tab 


Actually its the Gen 2 PMAGs that some are tight going into the magwell. 

I have had zero issues with the M3 Pmags and for some reason FDE Gen1 Pmags.  In fact I have it sighted in with my Aimpoint M2 and it has a M1 PMAG that inserts fine does not drop free but its my go to mag and I have a Old GI bandoleer with USGI mags from Bravo Company. 

For some odd reason its the Black recently made M2s that are giving me the most insertion issues not the M1s. 

I know K.O.A.M, I had a DPMS lower and a BCM upper at one time and it ran well with the H buffer and he was surprised on it running during the 3 day class.  I sold it to buy a Henderson Defense M4gery when they made them.  That is why I did not have an issue getting one again.

Ironically I have been pulling M2 PMAGs in and out of this lower and the troubled one is okay now and a lot of issues with mags are better.  Do not drop free but they are not sitting better in the magwell.  I do prefer the DPMS magwell to a Anderson I put together (bought two before my deployment) that has a real loose Magwell.  



Well this is an odd issue.  My 2017 PMAGs 15 of them all fit and fall out with out any issue.  Tried a 2007 OD Green Window fit fine and slide out fine empty.  Hung up a tad when full. 

I am wondering if there might be an issue with buying PMAGs from PSA and buying PMAGs from other places.  I got these 15 of them I bought from DSG Arms vice PSA.  The DSG I had put on backorder in Nov 1, 2016 with DSG while I was on deployment.  They were made in Feb 2017.

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