What I really don't understand about this argument, is if hard to regulate guns/drugs or anything illegal, it seems completely impossible to actually stop a bullet black market! If you could get your hands on 20 bullets (a really tiny amount!), you could most definitely cause a tragedy.
I'm not saying regulating guns is the solution, it may or may not be, but regulating bullets? That seems naive.
What people don't seem to realize is that ammunition is simple to manufacture at home with untraceable materials.
Lead bullets? Go down to the auto shop and ask for a stack of their discarded wheel balancing weights. Take them home, melt them down, and pour the molten lead into home-made dies.
Casings? Gather discarded casings and reload them. Dies and tools are commercially available. If there's a shortage of casings, appropriate dies can be relatively easily made and brass can be molded as needed.
Gunpowder? People have been making black powder at home for centuries. Smokeless powder is more difficult, but nitrocellulose is not that complex.
Primer? Boxer primers are US Patent 91,818. Berdan primers are patents 53,388 and 82,587. Active ingredient is potassium perchlorate, which is easy to get.
Regulating bullets will have negligible effect anyway.
I'm not saying regulating guns is the solution, it may or may not be, but regulating bullets? That seems naive.