From the 1895 Winchester catalogue, they say the 44 WCF bullets were pure lead.
Maybe you are doing this already, but for testing different loads and cartridges, may I suggest five-shot groups at 100 yards with at least two targets shot per load. I guess I'm a bit of an 'accountant' when it comes to load testing, but I'm busting with curiosity as to what these groups actually look like.
I find that 100 yard testing really starts to separate the good loads from the poor. If possible, I would love to see photos of the 100 yard targets labeled for the different loads you are testing so I can visually compare the performance of the different cartridges.