I have found range scrap to be a good free source also. However for me not so consitant.
The range that I get most of my range scrap from is a proverbial mix.
It contains slugs,muzzle loader balls, and all kinds of pistol and rifle ammo including home cast. (I have even found some "Elvis Ammo" PC Zinc .223. Which I toss.)
I have been putting the Range Scrap into pucks and testing BHN. They can range from 6 to 16 BHN depending on what I pick up that day.
So I pick out anything 9 to 12 and put back for the 357.
Anything less then 9 goes for my muzzle loader balls, and gets mixed 50-50 with lead roof sheeting and 1%tin. Just kinda makes them just the right size and weight for my 50.
I imagine the stuff I am picking up after local CCW classes probably would match your chemistry.
However thanks to a generous gift from a member here,, and also some scrounging I did amongst my old car days buddies. I have amassed a little over 200 lb of mostly vintage, mostly lead coww.
So COWW are still out there. You just got to throw enough inquiry's out there, and see if any stick.
I am in the process of melting them down in small batches and fluxing them clean with saw dust.
Then one day have a smelting marathon, and try and mix the COWW's into 1 big batch of chemically identical ingots. So I can start making my own bullets for the 06.