I met with an old collector earlier today. He offered me an ammunition can/box for 200 rounds of linked .50 caliber. It is WWII vintage and appears to be made of brown plastic or the same material as a helmet liner. It has rollers on one side and an opening on the same side. I thought it might be for an airplane (he thought a P-51 wing can). He also offered me 200 linked .50 cal brass with projectiles (not live). Any ideas on what the box is for and what the stuff is worth? Thanks!