A budy of mine recently got into casting and is haveing trouble with bullets droping at less than they need to be. The mould cavities are .456, same one as mine, and he's using pure WW, I'm using about 4 parts ww to one part soft lead. I'm not sure what the problem is, maybe build up of release agent in the mould as we had some trouble getting bullets to fall out. We seperated the stick-on WW to save them for round balls and such. We're both casting at about the same temp, but mine drop at .453-.454 and his drop at .450-.452ish.

Thanks

You'd have to be using some kind of realy heavy release agent to loose that much diameter....doubt that's it unless you can see it layered in the mold.

If the melt and mold were both at the proper casting temperature, it's probably just the mold and it could be the mold is simply mis-marked. You don't say what brand the molds are, if one's Al and the other Fe, you have to adjust your melt & mold temp accordingly.

WW alloy should fill out the mold better than pure lead because of the Sn in it, WW also has less shrink. I usually add about 3% WW to my pure lead balls just to get the casting benefits.

Just curious, have you checked the balls for roundness?

Before assuming the cavities are the same just because the moulds are marked the same try casting both with the same alloy at the same time. Chances are good they are really different diameters to begin with. Theoretically your bullets should be smaller as your alloy has a lower percentage of Antimony due to being diluted with Lead. Casting temperature also has an effect on final diameter.

In the LYMAN CAST BULLET HANDBOOK they give a list of diameters for some of their molds, using different alloys! Sometimes I play with alloys while trying to go up or down in diameter. If your mold is undersize; sometimes you can cast an old drillbit into a bullet and lap the mold up to a greater diameter by rotating the bullet in the mold (slowly) using common toothpaste!

Think we got it sorted. It apears to mainly be build up of mould release. Cast bullet and a screw and drill and commet and water seems to have fixed the problem.

I should know better, but I checked mine and the last batch of bullets are undersize. Now I've got close to 2000 bullets to remelt and recast. From now on I'm checking the dia. and not assuming just because they casted the rite dia. in the past they still will. Well live and learn. And from now on the only thing I'm using the mould release for is the sprue cutter and the top of the mould, and I'm applying it with bullets in the cavities to keep it out of them.

My mould did cast a slightly larger, .0005 bullet, but then it's got 7-8000 bullets cast from it and it may just be wear.

Think we got it sorted. It apears to mainly be build up of mould release...
I had the same problem a while back. Was using Midway Drop-out mould release. It's basically carbon in a solvent that I sprayed on the mould blocks. It's really easy to get too much on, and get undersized bullets.

I was able to clean off the mould release with carburetor cleaner.

Now, I use a butane lighter to smoke the cavities. Works well, but it's almost impossible to get so thick a layer that the bullets are undersized.

Don't use a candle or fluid lighter to do this - it leaves an oily residue that will prevent the lead from filling in the corners.