No idea on China, but the lead hardening alloys in late 14th century Europe included tin, antimony, and arsenic. I got interested as I was a not-particularly-well-funded teen competing with handguns - so I cast/loaded my own rounds, harvesting lead from the backstop in the club indoor range. I got interested in what was in that - in the sense of how toxic. Finding arsenic as a potential hardener got me interested in how far back that went, and whether there were known mines and trading routes (like with tin for bronze in much earlier Europe). I never found anything definitive, other than it already being in use in the 1300s.

I had thought that Gutenberg's primary contribution came from a hand mold with interchangeable parts (as opposed to one for each character), hadn't really thought about oil based ink or paper - so thanks again for that.

I can't tell you, well anything, about how the Chinese cast lead - or alloyed lead. I know they cast bronze, but that's about it (and that comes from wondering who came up with trunnions).