Lead/tin alloys will not harden. You need arsnic to cause the hardening process. You can get the requisite arsnic by using bagged shot, or by adding WW alloy to the mix. Be careful not to get WW labeled with a Z in the mix. Zinc is not user friendly and will contaminate the pot as well.
WW of antimony/lead mix can easily be hardened as below.

I used to shoot a mix of 50/50 WW and pure lead in my .50 Alaskan Rolling Block, which oven hardened to Brinel of about 24, (linotype is about Brinel 22) while straight from the mould, non-hardened, shot just as well and expanded like mad. At 1,800fps, there was no leading with non-hardened, 'soft' bullets. I didn't push the soft bullets(brinel 7 or 8) any faster than that. The combination of large bore and low pressure (slow powders) allowed the soft bullet shooting.

50/50 WW and pure should water drop about at about Brinel 20 to 24 - plenty hard enough for anything a DR in .40 or .45 cal will dish out. When I water drop bullets from the mould, I use a 5 gallon can with afolded towel in the bottom. I also have a sheet over the top of the bucket with a slit for the bullets to drop through. You absolutely don't want any splashes of water to enter the lead pot. BLOOOOOM - molten lead everywhere. It burns. I had a mopth fly into my lead pot last year and I wore about 6 pounds of lead. It emptied my 20 pound pot instantly.