03-16-2012, 03:06 PM
The issue that you'll find with any mags designed for 5.56 is that the vertical ribs on the sides of the mags are designed to handle the narrower diameter of the 5.56 round. Consequently, when you try to stuff the larger diameter Grendel round in a 5.56 mag, the Grendel rounds can't stack properly and begin to buldge the mag like ttrmike wrote. The 10-round ASC mags have a much shallower rib that allow the Grendel rounds to stack properly, so those are your best bet.