Thanks to the new DLC weapons it's real easy to get a lot of military grade ammo.     In the Lost Tunnels you can find a volt driver near the bandit's campfire.   Pick it up and trade it at Market for an auto shotgun and get over 100 rounds back.  Or if you like the volt driver, go ahead and keep it at least until Armory.  When you meet Andrew the Blacksmith there will be another volt driver and the heavy auto shotgun on his bed you can take.   Trade your original volt driver for a Duplet at the weapon shop if you still have it.   Then go back to Andrew's room, take the one you don't want and trade that for a Duplet as well.  Hell, if you don't want either of the new weapons trade the other one as well.