There was a time when a man could go into any hardware store and buy four cartridges to go deer hunting. Then the 1968 Gun Control Act required record keeping of all ammo sold, so hardware stores began to require you to buy a full box.
You also could not buy handguns, rifles or shotguns across state lines.
Then in the 1980s, Ronald Reagan signed a new law that did away with the record keeping of ammo, and allowed you to buy rifles and shotguns only across state lines.
That's really inconventient, not to be able to buy a firearm from your local gun dealer.