How soft for Cowboy SASS shooting?

[GSSP]

New to Cowboy shooting but not casting. I've got about 600 lbs of pure lead sheeting used in hospital X-ray room walls and 30 lbs of tin cut wire pieces from Rotometals. Trying to figure out what mix, between 1:16 to 1:40, lead to tin ratio for Cowboy loads running as slow as 500 fps from the Ruger Vaquero's to 850 from the 20" Uberti 1873. I'd like the Tin to last as long as possible but don't want to go so low on the tin mix I might get leading.

HBO (Help A Brother Out)

[earlmck]

I don't see you having any leading problems with those velocities even without adding tin, though the tin makes the casting go easier. That said, I use 1:30 for those purposes because of the nice way it casts and works for me.

[fecmech]

As long as you are using a decent lube and getting acceptable mold fill out I wouldn't use any tin. The tin will only matter for mold fill out, leading is a function of lube and size. For what you're doing I'd cast hot with pure lead and tumble lube the bullets.

[Outpost75]

1:40 casts well, giving good fill-out of the mold cavities and is economical. Casts much better than pure lead, but is not too hard for use in muzzleloaders or cap & ball revolvers. Ideal at black powder cartridge velocities with either BP or mild smokeless loads.

[WALLNUTT]

I use 1-25 at 1350fps with no leading. As others have said use just enough to aid casting.