Rcbs mold

[bosbill]

I have a RCBS mold for a 201 grain 45 ACP semi wad cutter that I purchased as NOS I don't seem to be able to get a flat base. I don't really have a problem with my Lyman molds once they get up to heat. I have tried this mold from 650 up to very frosty temperature. This is with wheel weight material. Any suggestions?

[Marlin Junky]

The mold is likely trapping air near the top (base end). Try loosening the sprue plate to the point where it opens under its own weight and if that doesn't fix it, put a tiny bevel on the edges of the blocks that come together to form the boolit's base seam with a sheet of 600 grit paper on a glass plate. Also, make sure all the vent lines are unobstructed.

MJ

[Calamity Jake]

Yap MJ nailed it!!_______________________ Venting

[Le Loup Solitaire]

MJ has it absolutely right. The sprue plate should not be tight and should swing free on its own weight when the blocks are tilted. But no up and down play/slop either. Another trick that might help is the thickness or diameter of the pour stream. If it is too thick and fills the diameter of the sprue cutter hole then it will also trap air. Trim it a little by adjusting the valve so that it is a little less in width than the hole itself. Enjoy casting and the mold as it is a good one. LLS

[Echo]

On one of my molds I had to stroke the top mating corners with a stone - just enough to put a bright edge on the corner (top mating edge of each block). Not enough to call a bevel.