I know this has been done before, kudo's to the guy who thought of using mp7 mid cap mags. I did 2 of mine today and simplified the process, after trimming down the back edge of the insert mag with a 115mm grinder (makes quick work on plastic!) placed empty mag case in gun slid in insert for fit to hop unit, measured gap at the bottom made a plywood block to fit, also slid in stick like piece to hold top of mag in place, now there is a bit of side movement and I will fill gap with a splurge of silicone when satisfied all is well with the mag feed.
Measurement of bottom block is 50mm wide, 22 mm thick, height has a slight wedge shape, so 55 mm high coming down to 50mm. The stick piece is 75mm long, 20mm wide, 8mm thick.
Andy
I discovered on the second one, I didn't need to grind off as much as I did with the first one (see pic) both mags fire fine no more bloody wheely, wheely! Will infill with silicone when I can remember what I've done with it!
