I'm no expert but my understanding is that ww have a lot of tin in them anyway.
Wheel weights contain a minimal percentage of tin required to enable the antimony to alloy with the lead.
A little extra tin doesn't hurt anything and makes the alloy flow a little better in the mold, but coww is an excellent bullet alloy just as it comes once your casting technique is perfected.
It can be mixed 50/50 with stick on ww, pure lead or range scrap and have an excellent alloy for handgun loads.
For HV rifles straight coww works well when water dropped, but the long rifle molds do benefit from a little more tin...tin lowers the melting point.
Generally, in an antimony amplified alloy, the tin does not function as a hardening agent, it is an alloying agent.
