Been casting my own lead hammers for years. While bullet casting can use hardners, I prefer a softer hammer for machine work. I have a hammer mold, don't know if it's a antique or if you need to look in a fishing supplies or gun stock outlet. I have both bullet molds and fishing weight molds, so it probably came from somewhere like that.
I use EMT, thinwall conduit, for a lot of purposes. It does have a seam so can't be used for pressure pipe. It is cheaper than copper pipe, if you have it on hand. But, it works well for hammer handles. I stuff a piece of cardboard folded up into the pipe about an inch. The pipe works well enough for chill stock with the cardboard in it. Then cut the handle for where it's used, usually around 6-8 inches. The cardboard gets left in place. I have used cheap ratchet handles, but the pawn shops are right proud of them. Like they're made of gold or something. I just have to keep an eye out for dropped ones.
Normally, I use tire weights with a little "whatever" cooked in with it. I have used a mix of lead and tin to make solder but that's usually harder than I like for hammers. Most times the "whatever" is a partial bag of shot or salvaged bullets from the downrange stops. Tin is expensive, and I don't know where one would find it in usable quantities. I misappropriated my supply a long time ago and just sit on it.
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