a few years back i got one hell of a deal with a rifle, boatload of mags and three drums. Little did i know, one drum was a 75 round and two were 100. Ive been googling and can never find 100 round drums? Am i missing something here? Its not the hinged back, butterfly key style (norinco). Any insight on whats up here? Was there a short run of 100rnd drums or something?