While going through some boxes I came across a container in which I had placed several rounds of what I believe to be military ammo, but for the life of me can't identify what it is. In looking at the headstamp, at the top is the number 85, at the bottom is the number 12 and surrounding the primer are three "hash marks", one being in the 3 o'clock position, one in the 7 o'clock position and one in the 9 o'clock position. Anyone have any idea what this might be? (I'm thinking it is .308, but not really sure). Overall length is 2.75 inches.
Thanks!!

The headstamp on military ammo usually doesn't indicate caliber. Rather, the codes indicate the production date and where (factory) the ammo was made. There's a reference to a "12" in the link below, but nothing else. I think the "hashmarks" you mention are a primer staking feature.

http://cartridgecollectors.org/?page=headstampcodes