Mold lapping

[greenrivers]

New member here, but old hand at casting and reloading and still finding that learning is more fun than remembering!
I shoot a number of cast bullets in several calibers, both rifle and handgun from .22 Hornet to .454 Casull, but my question is: What methods do you use to evenly lap bullet molds without rounding edges? Thanks for any info.

[Wally]

You cast a bullet in the mold. Some place a nut (as in nut and bolt) on the top of the mold where the sprue plate would be--you cast to it fills the cavity and then the inside of the nut. You then make a paste of an abrasive (valve grinding compound) you insert in the mold close the blocks and turn the nut with a wrench. Others drill a hole in the base of the cast bullet and attach a screw. You then chuck into a drill, add abrasives, & spin. I have tried the later...all one needs to do is to check their progress...How? You have to cast bullets from the lapped mold to determine their diameter. With Aluminum molds best to use Kitchen Kleanser/Comet as an abrasive as grinding compound cuts them too quickly and may well ruin your mold.

[runfiverun]

i use whitening tooth paste as a final polisher,others use flitz,or a paste made from barkeepers friend.

if i want to cut the mold larger i use lapping compound from the napa store.
warm the mold up and use a boolit made from linotype run a screw into the base and spin it with the drill [this works well on short fat type boolits].
the nut method works best with long skinny boolits.
take the time to pour some good boolits before making your lap.
check to see for sure where you want lapped out as the compund will migrate.

i generally put some compound down on a hard smooth surface and carefully roll the boolit through the compound getting it only where i want it.

[HenryC460]

I've got an aluminum paper patch mould that was dropping them a little to small, and oval shaped. I've gone with the drilled boolits with a screw in the base and silicon carbide grit (220 or 400 to start off with).

Chucked that screw in a cordless drill, and gave myself a headache.

What happened was that the lapping would work for a while, and then the mould would get leaded. I'd have an adhering lead patch that would tear a groove in the boolit I was lapping with, and the new, ungrooved boolits I was replacing it with.

I put on the Magna-Visor and carved the lead out with an Exacto-knife as close to the aluminum as I dared, but the lead patch was still there, and it wouldn't lap out. the lead patch still tore grooves in the new lapping boolits.

This is what worked: I bought some desoldering braid at Radio Shack. It's braided copper wire. I used 50/50 beeswax/Alox as an antiflux around the lead patch and melted it with a little circuit board sodering iron. As the lead melted, I pressed the desoldering braid on it, and it picked up the lead. The boolit lube seemed to help the lead bead up off the aluminum. It probably kept the desoldering braid from being 100% effective, but overall, the process worked.

Then I was able to get back to lapping, but I didn't run the drill so fast as before.