So does asbestos exist in the environment but you don't load that into your shotgun and shoot it either. Depleted uranium is a big part of the or that is used to refine high quality uranium for fuel rods and weapons. They just take the uranium that they want to use for fuel and the low level depleted uranium is made into bullets. When it goes through a hunk of armor, it is vaporized or at least aerosolized and put into the local atmosphere. That is very different from laying on or in the ground locked away so it can't be inhaled or ingested.
If you are interested in airguns then read some of the stuff written by a guy named Gaylord. He has a regular column in Shotgun news, and some other stuff on Amazon or web sites if u look around. When I first saw his column I thought "Airguns? In SGN? Seriously?"
But once I found out that there are airguns that can hunt in Africa, I was a little more interested. There's one that shoots a heavier bullet than my Kodiak. Pow, zoom, to the farging moon!
Look around local thrift stores for things made of pewter.. Great source of Tin and a little extra antimony, When the SHTF you can just melt the posts off of old batteries (pure lead and mix 50/50 with the pewter you scrounged and have good bullet alloy.
I have collected close to 180lbs of pewter and over 2000lbs of wheel weight alloy and maybe 100 or so lbs of pure from cast iron plumbing joints. (my BIL is a contractor and he collects the pure lead when he finds it.)
for close range target shooting, what about plastic? sorry, I don't have any first hand knowledge with this, but there are injection molding devices suitable for the home hobbiest workbench. And, the plastic beads can be purchased by the 50lb bag, or by the train car.
You could try your local public works dept at your town or city. They might end up with lead pipe from replacing old water mains and could be happy just to get rid of it without paying some sort of enviro charges.