Labor and time is what you have. Get the hardness pencil set. They're cheap, easy to find, and give Very Good Bhn results.
Lower the pot to near empty. Measure small but equal portions of RS and COWW's (foreshortened to just WW). SOWW's remain SOWW's (save - you know it is near pure and ~6 Bhn). Obtain and add no more than 2% of new Tin (Sn) by weight of the total of RS + WW. Melt and pour into boolits. Air cool some. Water drop some.
Check the average weight of (say) 10 of both cooled type boolits. Write it down. Check the pencil hardness of this alloy (maybe 11 to 14). Write it down. Call this alloy mixture 49/49/2 percent of RS/WW/Sn. It is correct for the components and a starting point. How do they shoot? What caliber, what powder, how much powder, how deeply embeded are the boolits in the case, COL, did they lead the barrel, was the barrel slugged, were the boolits lubed and sized, to what size, what lube, etc. Write copious notes.
Do this again mixing a small batch of 45/55/2 of RS/WW/Sn [Wow! That's 102%! Edited to 44/54/2]. Keep Tin that you add to no more than 2% (you can add less tin later when testing other batches). Check weight and hardness. Going up/down? How do they shoot? Write it all down.
Adjust the next batch to suit. Keep copious NOTES.
Adjust tin to 1% added and rebatch some of the alloy trials above. Keep the same notes.
I am guessing your alloys will all probably fall in the 11 to 14 Bhn category due to the mixture of constituents. IMO, your "grab bag" of RS, as a starting point for each batch, is just as likely to be like the former batch than it is to be wildly different.
Assume the best. If a batch's result is significantly different from previous batches (I would be surprised), try the batch again with a different handful of components. Anomalies can present themselves, but the law of equal distribution is likely to control.
Good luck. Successful shooting. And let us know if this works for you.