By my measure, it's likely that your lead is pure or pure enough for M/L's. Have never heard of Willard. You can buy a hardess tester for lead but not worth the expense. Initially I use the scratch test with my thumbnail. I may also use my auto center punch and measure the indent. You can also take and equal sample of a known lead and your Willard together and put them in a pan on a burner. The pure lead should melt first if the Willard, is an alloy. You have to watch them closely and you may have to repeat this test just a few times.
Personally, I would give the benefit of the doubt to the Willard, being pure enough for M/L's.
Be Safe !!!