I only cast for my BP guns which use pure lead, but cast bullets for high velocity metallic cartridges require tin and/or antimony. I believe wheel weights and linotype are composed of the proper alloy mix. A lead hardness tester would be a useful tool if you plan on casting your own bullets for non-BP rifles. Hardness is measured with a tester which drives a hardened steel rod into a bullet, and read on a vernier scale in arbitrary units running from 0 (Brinell 5) for pure lead, to 10 for linotype (Brinell 22) Wheel weights vary from 7 to 9 (Brinell 10-13) A hardness of atleast 6 is required for medium handgun velocities, over 8 for magnum handguns and gas-checked rifle bullets. Someone else out here can probably supply you with more information on acquiring and mixing tin/antimony with pure lead, as well as bullet sizing and gas checks.