Tax ammunition sales by weight at $3,000/lb

Guns don't kill people; bullets kill people.
The lethality of a round is proportional to its weight, not its caliber. A 0.22 is far less lethal than the 0.243 rounds used in Sandy Hook and in Orlando. At $3,000/lb, a 0.22 bullet is $22.50 while the 0.243 = $135 each.
Late Sen. Patrick Moynihan tried to get this passed in 1993.
Law abiding citizens paying hundreds of dollars for a weapon for safety would only pay about as much, or less, to load it. Make an exception for licensed gun clubs and gun ranges where people can shoot recreationally, on the condition that number of rounds used there are reported and tracked.