I use the 2.5 lb ingots, for a couple reasons. They fit easily into my Lee 4-20 pot and they stack up between my 2 x 4 's well:
I use Linotype to mix with my pure lead to get a BHN 10 mix, which is what I pour at. Once I cast, I powder coat with Harbor Freight Red powder paint, and then size.
I use Brinells method to measure hardness, but it requires a drill press, bathroom scale and a micrometer:
Just be prepared for the learning curve. It takes a while to master smelting, pouring, and powder coating.
.38's are a lot more forgiving.....