A few months back I talked with James Malarkey with XS Products about their X-15 50 round drum magazine for firearms that use the STANAG AR-15/M16 style magazines. It might be no surprise to most of you that this high capacity magazine is always sold out and they take pre-orders for later months. I ordered mine back in October and it showed up last week.
I currently am in the testing phase with this magazine and plan to have a full review in the coming months.