"Sufficient" for what? The answer for "no more available, better stock a lifetime supply" versus "how much do you keep on hand for weekend range visits before you re-order next month" is gonna vary a lot. Also, what is the purpose and caliber of the firearms? The .30-06 bolt action deer rifle may get a whole box of 20 shot through it every year between pre-hunt sight verification and the actual hunt, a few hundred rounds would be an almost lifetime supply for that gun and the tasks it is normally used for. A belt fed 1919A4 with a crankfire attachment? Real easy to go through a thousand rounds in an afternoon, that's just 4 belts.