Except for state laws-- usually california, no limits on ammo purchases. Purchase 5 million rounds if thats what you need for um, deer hunting. Nothing over 50 cal, but 50 cal is fine. Mount it on your pickup truck or your own armored vehicle I guess. 50 cal ammo is 3 bucks per round for the cheap stuff so that adds up. Not a gun for the poors to own. You can own a tank if you want to, but theres a lot of laws around making it street legal, depending on the tank's weight.

Operating a tank is a paperwork nightmare, which is another reason why Americans are so cynical about their government.

(/s)