I was bored yesterday, so I decided to tap my inner Dr. Frankenstein and created some custom 20 round Gen M2 PMAGS (in OD Green, of course.) I took inspiration from the Midwest PX 15 round design and using my Gen M3 20 rounder as a template, I went to work.

First, I cut the mag just below the third rib from the top. Then sanded and ensured the base of the mag was level. When all is said and done, there should be only a millimeter or two of mag protruding past the bottom of this rib. The rib serves as a make-shift guide for the baseplate and has a fatter surface area for any roll-pin pilot holes. It also allows for a stronger bond with super glue/epoxy, but more on that later.

At this point, if you were to affix a floorplate and load up the mag it would hold 20 rounds, but would be a tight fit on a closed bolt. To help this, I trimmed about 1/8" off of both legs on the Gen M2 follower. You need to be precise here, and ensure that you remove any excess trimmings and sand and clean the area thoroughly. (Removing a very small amount will not affect travel in the mag.) Yes, you could probably avoid this step if you cut the mag a little further below the third rib, but then you'd be sacrificing the extra strength the rib offers for your roll pin and epoxy. There is no need to cut the mag spring, as the gen M3s use a full size 30 round spring. It only helps ensure more reliable feeding.

Next, I drilled a 3/32" pilot hole through the floorplate, mag, and inner locking plate. Finding the right placement takes a few tries, but the halfway mark on the edge of the Gen M2 floorplate (right where it changes angle) allows the 3/32 1-1/4" roll pin to slip right under where the spring locks to the inner locking plate (at least that's the case with a magazine blocks branded Gen M3 locking plate). This length pin is slightly longer than the width of the floorplate and needs to be trimmed slightly to seat flush.

Lastly, I constructed the mag. You could just use the roll pin, or reinforce with a secondary pin, but since I have a ton of Gen M2 floorplates, and dont really care about destroying them, I opted for securing the floorplate with industrial grade super glue (HFT brand). The roll pin serves as the backup securing method.

The mags feed and function perfectly and offer another option for bench shooters or all-around 20 round freaks (I guess I'm one now, too). Hopefully this helps a few folks out. Some pics below. Also a side by side with one of my Gen 1 straight 20 rounders.

Fun Fact: trimming the self-lubricating / self-leveling Gen M2 follower emits a "mint-like" odor. It smells amazing...

I was bored yesterday . . . . .

Why not?  Nice job OP.

Pretty fancy work there OP!

Thanks guys. I like the curved 20 round profile. This would also be a good option for folks in ban states who would like a slightly longer mag than the 10 round "choad" pmags. Without the Gen M3 nub on the back you could just throw a mag block into the mix and use with your choice of pouch for easy access. Hard to do that with the super shorty 10 rounders.

"Necessity is the mother of invention"