I did some searching around here and hadn't seen this posted yet, so here it is. I did notice several people have or use the Smith & Wesson M&P 15-22 for Appleseed, so I thought it might be of interest.
For anyone with an M&P 15-22: If you haven't been over to the Smith-WessonForum.com you should check out the "M&P 15-22 Mag development" thread. The guy there is designing a new high capacity low profile magazine, that if it lives up to the hype will be pretty amazing. He's nearing the final stages of development and about ready to release the final product information and start a preorder/group buy.
The speculation so far is that the magazine will be up to 50 round capacity, low profile enough that it won't extend down below the bottom of the pistol grip, and that the loading system will be fast and easy without requiring a speed loader tool or load assist button. Cost should be below $40.
If you're at all interested head over to the thread at: http://smith-wessonforum.com/smith-wesson-m-p-15-22/275185-m-p15-22-mag-development.html
He is looking for people to let him know many they are interested in (via email address he posted) to figure out the initial production run. Hopefully more interest means more production, with a lower cost, while helping to recover the development cost.
Also, the guy developing the magazines is actively involved in the thread. A quarter of the almost 600 posts there are him responding to question and suggestions. I searched within the thread for all posts with him as the author for a quicker read through of the entire thing without a bunch of extra clutter.
He is also trying to get as many of the standard capacity magazines made as soon as possible. Later there will be reduced capacity magazines available with the same design features.
that's interesting
Ramline made a compact 30 and 50 round double stack mag for the 10/22 back in the 1980s. It's main problem was the feedlips not the feeding mechanism.
He says he has over 4000 rounds through the prototype. If it works well, hopefully it can be adapted to other models as well.