Military is already in the process of switching to lead free. That is being driven primarily from the large amounts of lead that accumulates at the firing ranges.
Those "lead free" efforts with Bismuth-Tin bullets will fail just as previous attempts have.
Bismuth-Tin is LESS environmentally friendly than lead. Calculate the environmental costs of mining Bismuth and Tin, both of which is quite high, and lead comes out as the more environmentally friendly choice.
Bismuth is actually quite scarce, only about 8 times as abundant as gold. So I have no idea where the hell they are getting the supply.
Looking at current metal prices, this is the best info I could find:
Lead is selling for about $1,600 a ton
Basic steel is selling for about $415 a ton.
Copper is selling for about $6,300 a ton
Tin is selling for about $17,000 a ton
Bismuth is selling for about $16,000 a ton.
The supply of Bismuth is heavily dependent on recycling old Bismuth. Start using it like this in bullets on a massive scale and the price is going to greatly increase as demand outstrips supply.
Then again, watermellons don't care about whether something is good for the environment. As long as it "feels good" it must be right.
Once the ammo bills start piling up lead is gonna come back VERY quickly.