Thank so fellas! I've been looking for blind mags for the stagger feed and haven't had much luck for some reason my google due is broken! I'm not 100% sure on the Grendel or a 6mm Fat Rat but either way I ordered a bolt head from ptg as it's going to be chambered in one or the other and both use the same case. I've got to get my 300wm finished first BUT planning for the next one :) Later,

Kirk