Best material to make a knock out core mold for PURE lead

[Hexbasher]

First of all, I'm a machinist so I don't care what's easier to machine or get a better finish.

I only care what metal works the best with 100% pure lead (I'm swaging slugs)

I have on hand 6061 and 7075 alum, brass, and afew grades of steel (mild, 4140, 4340). Plus lots of grades of SS, bronze, etc. no iron on hand but I could but some.

This is a mold is going to be similar to Corbin's adjustable core mold

[Hexbasher]

Whatever fills out the best and doesn't stick too bad

The only venting that can be done is under the spur plate

[country gent]

With pure lead I would go with cast iron or brass. as they will hold heat better and longer than aluminum. Also consider giving the cavity a few thou taper top to bottom to help with release. a small mark on the ejector will orient the lugs direction for you. Im assuming this is to be a solid mould not split here.

[Hexbasher]

Yes Itll be a solid mold. A little taper makes sense. My cores are going to be less than 1/2" long and 0.348 in dia

im interpolating the bores ruff undersize to 0.347 (hone to size). If they taper maybe I'll leave that or try to hone that in