Where in blazes did you wind up with so much metal?
I posted a reply to this yesterday, but it was dead wrong, so I dumped it last night. CRS got me again.
What I should have said, instead of the nonsense I wrote, was that plain wheelweights are about as soft as you would want to get for this type of shooting. Nothing that you can do with what you've got is going to get more Sn into the mix, and Sn is what improves castability. It hardens a little, too, but not as much as the Sb that's already in the wheelweights. Most shooters start their experimenting with Lyman #2 Alloy, with a hardness of 15. If you can get some linotype metal, equal parts of it and Pb will give you something very close to that. The reason Lyman #2 is the preferred starting alloy is that many, if not most, find that their rifles handle it best anyway. If you get much softer (say, plain wheelweights) you may find a lot of leading, which kind of spoils the experience. On the other hand, it might work fine, in which case you've got it made. I have run across one writer who says his rifle does best with a 30:1::Pb:Sn mixture, and I dare say there are others. WW or 30:1 hve a hardnes of 9. So you can see what the idea is...get the softest bullet that you can as long as it doesn't lead the bore. Accuracy is the name of the game with these guns and cartridges, and leading the bore ruins that, to say nothing of being a royal pain.
Temperature is best found by pouring a few, see how they come out...if too cool, raise the temp. If too hot, back down. The coolest temp that gives good bullets is the right one.
Incidentally, bullets made from plain WW can be hardened after casting and sizing (but NOT lubing!) using your kitchen oven. Lyman's Bullet Casting Handbook tells how to do it...hardnesses as high as near 40 can be reached.
All this is really simple stuff, but has all kinds of variables, mostly associated with the guns themselves. So the only way to get what you want is to muck around with these things until you get it...there's no hard-and-fast answer.
