I know and have used basic 95-5 lead free solder to add to the mix for better flow and fill out.
I just bought 6 one pound rolls of Oatey silver bearing plumbing solder for a song.
The Oatey msds lists tin as the major, and up to 5% each of copper, bismuth, and silver.
Any harm or gain in adding this for the extra tin to my clip-on wheel weight alloy?