I brought this up in another thread, but I thought I would share my AW magazine 12rnd modification. Depending on cartridge (I run 6xc), most people can already load 11rnds into a standard AW magazine, but who doesn't want MORE ROUNDS right?
Step 1: Cut a hole in the box
---After removing the spring and follower from the magazine body, I used the bottom of the spring as a guide to trace the outline, roughly centered, on the bottom of the magazine. This does need a little wiggle room, but I would say I left about 3/16-1/4" of material all the way around the edge of the magazine. I drilled the corners out, then connected the dots with a Dremel cutoff wheel. Total time, 5 minutes.
Step 2: Put the spring in the box
---As easy as it sounds, place the spring/follower back into the magazine, with the spring hanging out of the bottom. I stretched out the flat sprint a little bit, but nothing crazy.
Step 3: Put the Extension on the box
---Again, as easy as it sounds. I slid on the Area 429 magazine extension and locked it on with the supplied set screw. While this mod does not take full advantage of the A419 +4 extension, the cutout in the bottom of the magazine gives just enough room for the follower to bottom out on the bottom of the magazine, rather than stopping on the compressed spring. This allows me to fit 12rnds, with about a 1/2 round compression that allows me to seat a magazine on a closed bolt.
Testing - I've ran about 500 rnds through this magazine, all loaded to 12rnd max, through my boltgun over the last 2 weeks. I've had absolutely ZERO issues.