It depends on the expected velocity. If you are sticking to mild loads in the Sharps, stay with the lower alloy levels.
As a general rule of thumb 2% increase in Tin is equivalent to a 1% increase in Antimony as far as hardness is concerned.
The higher the Tin/Antimony level the harder the bullet. The harder the bullet the faster you need to shoot it for proper results. Harder does not necessarily mean better if you are shooting moderate velocities. Keep in mind the original 45-70 loading 405 gr bullet at about 1400 fps used a pure or nearly pure lead bullet.
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