MAC10 Talk - Converting Argentine PAM2 magazines for the M11/9

Converting Argentine Magazines for the M11/9

Converting Argentine PAM2 Magazines for use in the M11/9

Submitted by MAC10 Talk Member StealthyBlagga

Like others on this forum, I ordered a bunch of converted Argentine PAM2 steel magazines for my M11/9 from Recon Ordnance. These PAM2 magazines are converted to work with the M11/9 by milling a magazine catch slot in the back of the magazine body, and slimming down the magazine body. Recon Ordnance also does a nice job of reparkerizing after the conversion. While many M11/9 owners are fortunate enough to have these magazines run right out of the box, in my case I had to do some work. The following steps allowed me to get my gun and steel magazines to run flawlessly together, with both the OEM (fast) upper and the MAX-11 slowfire upper. I hope others will find my experiences helpful.

Tight Fit
Original PAM2 magazines are too wide/deep to fit the magazine well of the M11/9. During the conversion process, the sides of the magazine body are sanded down to fit. However, in my experience, even the converted magazines are still pretty tight in most guns.

My first step was to inspect carefully how the magazines fit in my lower. What I found was that the magazines would start off entering the magazine well easily, but then they would bind about half way in. Interestingly, after about 1-2" of resistance, the magazine would again move more freely ! Upon closer inspection, I noticed some rub marks on the inside-rear of my magazine well - you can see them in the center of this photo (the two silver spots either side of the grip screw bushing):

These looked to be high spots left when the grip screw bushing was welded in place. I filed/honed these spots flat, after which I found that most of the magazines went in and out much more easily. Still not a true drop-free fit, but loose enough. Some magazines still needed a little sanding around the body to get them to fit the way I liked… if you need a drop-free fit, then you may want to invest more heavily in sandpaper than I did.

Feed Problems

With the improved fit, I found that the steel magazines ran fairly reliably in my M11/9 with the OEM upper. Still not 100%, but close. However, the magazines would not run at all with the MAX-11 upper. Specifically, the rounds would consistently nosedive into the gap between the feed ramp and the chamber. The failures with the slowfire upper were surprising; typically, the slower cyclic rate would be expected to be less demanding on the magazines, because the cartridge stack has more time to move into alignment with the bolt before the next round is stripped off. In contrast, my Cobray-marked Zytel magazines ran flawlessly with both uppers. For the record, all my testing was done with Winchester “White Box” USA9MMVP 115grn jacketed round nose factory ammo (the recommended load for the MAX-11).

At first, I was thinking of tweaking the feed lips to find the optimal feed angle. Some people have indeed found this approach to be workable. However, when inspecting the steel magazines alongside the Zytel magazines, the feed lip engagement was clearly different. Here are some comparison photos, steel magazine on the left and Zytel magazine on the right:

My observations were:

The location and feed angles of the top cartridge looked very similar; if anything, the steel magazine looked to be marginally better aligned with the chamber.
The Zytel magazine had what looked like an integral feed ramp, which could help in preventing the cartridge from nose diving.
The steel magazine's feed lips were much longer, and held onto the cartridge later in the feed cycle, compared with the Zytel feed lips.

In loading the magazines, I also noticed how a lot more force was required to slide the cartridge against the steel feed lips compared with the Zytel. This could possibly have been robbing the bolt of momentum, perhaps causing feeding problems.

Lastly, I removed my bolt assembly, reassembled the gun, and inserted each loaded magazine. I then used my fingers to push the top cartridge forwards until it touched the feed ramp. Here are the pictures:

Zytel	Steel

Again, the longer feed lips of the steel magazine clearly held onto the cartridge until later in the feed cycle. Note also how brass was being abraded from the cartridge case as it slid against the inside of the steel feed lips.

Based on the above data, and my experience troubleshooting pistol magazines, I suspected the problem lay in the feed lips of the steel magazines. Specifically, they were too rough and too long, thereby inhibiting the movement and release of the cartridge during the forward stroke of the bolt. Rather than bending the lips (they looked too beefy to bend easily), I decided to remove some metal from the front of the feed lips so as to replicate the profile and release point of the Zytels. This was quick work using a Dremel with sanding attachment. The photos below show how the feed lips compared after the modification:

Top: Original steel magazine. Bottom: Modified steel magazine.
Top: Original steel magazine. Middle: Original Zytel magazine. Bottom: Modified steel magazine.
Left: Original steel magazine. Middle: Original Zytel magazine. Right: Modified steel magazine.

Upon test firing, the modified magazines definitely fed better in my MAX-11 than the original unmodified magazines, releasing the cartridge earlier in the feed cycle like a Zytel. However, even though the modified magazines fed more reliably, they still suffered from the same fundamental feed malfunction about 20% of the time (1 in 5 shots). Clearly, the magazine feed lips were not the whole story.

When I compared the feed ramp area between my OEM M11/9 upper and my MAX-11 upper, I found that the gap between the feed ramp and the barrel throat of the MAX-11 was visibly wider than with the OEM M11/9 upper. Moreover, the feed ramp and the barrel of the MAX-11 were not well aligned; the feed ramp sat a little low relative to the barrel throat, leading to a pronounced and sharp "step" that the bullet nose had to get over during feeding:

I am fortunate to live within a few miles of Richard Lage, designer of the MAX-11 upper, so I ran over to his place with my gun and a set of calipers. I found that, in comparison with Richard’s gun, the top of my feed ramp was significantly lower relative to the rest of the gun. I concluded that the feed ramp needed to be properly aligned with the chamber. Taking a deep breath, I adjusted the feed ramp on my lower; I removed my trigger group (to get clearance) and then used a small crescent wrench to tweak my feed ramp upward. I checked it by feel with my fingertip, tweaking a bit at a time and then reinstalling the upper and feeling with my fingertips to determine when I had minimized the sharp step between the feed ramp and the barrel throat. As a point of reference, I measured the distance from the floor of the lower receiver to the top of my newly adjusted feed ramp; it measures right around 0.70":

This misaligned feed ramp would explain why the Zytel magazines ran OK; Zytels have an integral feed ramp that would have diverted the bullet nose past the step to the chamber, whereas the steel magazines have no such integral feed ramp and thus are more dependent on the feed ramp of the lower receiver to get the rounds into the chamber.

There are some other consideration for feeding:

Although it did not cause me any difficulties, the vertical alignment of the magazines should be reviewed. In some guns, the combination of magazine and magazine catch can allow the magazine to sit low in the gun, thus creating a steeper-than-desired feed angle. In other guns, the magazine can sit too high, causing the bolt to rub on the feed lips, robbing it of momentum. Both issues are worth attending to if the previous steps do not make your magazines run 100%.
Some others have recommended bending the feel lips out rather than cutting them back. If you feel more comfortable with this approach, by all means try it.
Several people have recommended some combination of new magazine springs (notable, those made by Wolff for an Uzi magazine) and new followers (Lage and/or Zytels followers). I did not find this necessary in my case, but some people like them for their ease of loading (my magazines need a loader for sure), and they are certainly cheap enough to try.

Magazine Stops

After the Famous Sam’s 2006 AZ State Subgun Match, I noticed I could not remove the bolt from my MAX-11 for cleaning. Closer inspection revealed that the sheet metal of the MAX-11 upper, just below the ejection port, had become battered and bent inwards. The root cause of this damage was found to be the vigor with which I slam magazines home during a speed load; the steel magazine feed lips hit the bottom of the MAX-11 upper, causing the damage indicated in this photo. My solution was to install magazine stops to prevent over insertion of the magazines.

Normally, welding on steel magazine stops would be easy, and some people have been satisfied with this approach. However, the magazine well of many M11/9s can be soft, and steel magazine stops could peen the expensive lower receiver… not appealing. I wanted to find a softer magazine stop with a replaceable, sacrificial point of contact. My first attempt was to glue squares of aluminum to the back of the magazine body. The aluminum stops worked OK while they held on, but I could not find an epoxy that lasted through more than two subgun matches. My final solution was to weld on steel magazine stops and then place a rubber o-ring over the steel (the sacrificial part). Although time consuming and complex to fabricate, and requiring a TIG welder, these stops have proved to work very well.

Note also my use of bicycle inner tube to cover the magazine base plate – unless you like the bleed for your sport, I suggest you investigate this low-cost protective measure. The inner tube material works equally well for steel and Zytel magazines.

Ammo

My last recommendation is to avoid Wolf ammo. In my experience, the steel case and/or its polymer coating tend to drag a little more than brass cased ammo. While not a huge effect, I have found it can cause occasional feed stoppages because the rounds are a little tardy moving up the magazine body. Personally, while I use it for blasting, I avoid Wolf ammo for serious applications where reliability is important.

Happy Ending

After 15 months, thousands of rounds and numerous subgun competitions, the above modifications have allowed me to enjoy 100% reliability (with brass ammo) using both the OEM M11/9 upper and the MAX-11 upper. I have since sold all my Zytel magazines, as the steel magazines run so well I no longer need the plastic ones.

My sincere thanks go to Richard Lage, who took the time out of his busy schedule to work with me on isolating and resolving this problem, and also to everyone else who responded to my pleas for help.

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