Bismuth/tin for round ball.

[keith66]

Bismuth is not viable because it is a rare metal with very limited production from very few mines. It was used as a neutron absorber in the nuclear industry so one would expect most production to go that way.
It is also very brittle & frangible & liable to fragment going down the barrel. This was quite common with early non toxic shotgun loads where you fire 3's & dust comes out the end after its been through too tight a choke.

[BaskervilleDog]

Bismuth is not viable because it is a rare metal with very limited production from very few mines. It was used as a neutron absorber in the nuclear industry so one would expect most production to go that way.
It is also very brittle & frangible & liable to fragment going down the barrel. This was quite common with early non toxic shotgun loads where you fire 3's & dust comes out the end after its been through too tight a choke.

I wouldn't try Bismuth on it's own for the very reason you state but I am pretty sure that Rotometal uses Bismuth, Tin and Antimony by percentages. Some of the reviews on their site are from muzzle-loaders using patched round ball.

[DesG]

Bismuth is not viable because it is a rare metal with very limited production from very few mines. It was used as a neutron absorber in the nuclear industry so one would expect most production to go that way.
It is also very brittle & frangible & liable to fragment going down the barrel. This was quite common with early non toxic shotgun loads where you fire 3's & dust comes out the end after its been through too tight a choke.

Depleted Bismuth? Now there's a thought! Far safer than nasty old lead.

[Black Beard]

Pure tin is BHN 9, which is almost as hard as typical range scrap. It won't work as well as pure lead for muzzle loaders.