making bullet molds

[dmb25]

Hello I am getting ready to make some bullet molds on a CNC lathe and was wondering how I should change the diameter of the mold to allow for shrinkage. Thanks

[bob in the woods]

You say " bullet" , so am assuming not round ball .  What alloy are you going to use in the molds?
I know the shrinkage rate is different when I cast pure lead or wheel weights for my smoothbore.

[dmb25]

I worded that wrong meant to say round ball bold and I plan on using pure lead

[Daryl]

I would make them .002" larger than the finished size you want, in sizes of .54 to .75. In smaller sizes like .45 and .50, I'd go .0015", smaller than that, .001".

For instance, I have a Tanner 15 bore mould, that casts .675" in pure lead, and .677" (mould bored size) in WW alloy. My moulds are sprayed with moly bullet coating and thus the balls fall from them perfectly, most of the time.

[dmb25]

OK thanks

[Steve-In]

Put your radius in the program as a macro variable and make up different sizes.  You would only be limited by clearance of the bar.

[Squirrel pizza]

Taking into account the bigger the ball, the more lead to fill, more heat created, greater expansion of the mold itself. Leads to other problems. I tried for over a month to make one (bullet mold) for a 4 bore. 1750 gr.  Found it was easier to drill holes in an oak plank with a 7/8" paddle bit, fill with lead, split board to get the lead out, then turn the bullets in the lathe. Worked for me. Never made one for a round ball. I think you can order one custom made from Buffalo Bullet Co. Not very expensive but they have the metallurgy down to a science.