I have found that the best accuracy and performance accrues from soft bullets. With softer bullets, no leading occurs and consistent performance is more apt to occur.
DO NOT MIX YOUR VARIOUS LEAD SOURCES until, and if, you wish to alloy them at time of casting. In other words, only in small lots inside the casting pot.
I get the best results with pure lead and enough tin to permit the molten lead to fill out in the mold. This usually ends up being about 30/1 lead/tin. Even when using wheel weights in the mix, there is often not enough tin to allow the molds to fill out and I end up having to add some.
All this is to say, you will need a source of tin in addition to your pure lead. I purchase certified 50/50 bar solder in one pound rods. It is then very easy to figure the ratio of tin to lead since each bar has a half pound of tin in it. So, 14.5 pounds of pure lead and one 50/50 rod gives me a 30/1 alloy. This usually works.
I have come to think of tin as a substance that makes the lead more 'runny'. If I'm having trouble with molds filling out, I just dip a 50/50 rod into the pot to "lubricate" things and the mold always start to fill out.
There are many sources for certified 50/50 bar solder on the web and people often offer it for sale on ebay.
I have never found any reason to use "hard" lead in a gun. I have never added antimony to an alloy. Frankly, the mass of 45-70 bullets insures penetration regardless of the "hardness" of the alloy.
Use soft lead with only enough tin to make the molds work.