I posted this item earlier during my hello and I thought you guys might get a kick out of it. Basically, I bought 2 used Bazooka Bros American 180 drum adapters for $60 and modified them for various hosts including my new M&P 15-22. I've been using the contraption with E&L Mfgs 165 and 220 round drums. With the 17 spacer rounds necessary to lift the last round into the chamber, it will shoot 147 rounds from the 165 and 203 rounds from the 220 round drums. It has proven very reliable with both drums. I've has 2 FTF in the last 1500 rounds.

I'm not a manufacturer, just a garage tinkerer. I don't sell these but I'll try to have a instructional demo up soon when I get some free time. It should be possible for those with intermediate fabrication skills and tools. Most of the work was done with a hand saw, files, drill and a few moments on a TIG.