There is a shrink rule for cast iron and cast aluminum. Is there a similar rule for lead alloys? I know it would vary with the alloy. I seem to be getting about 0.002" shrink on a .38 caliber with 20:1 alloy.
Chuck

Toolmkr,---You are correct. I am asking about the shrink factor, not shrink rule. Bad choice of words on my part.
Chuck

Would you recommend getting the diameters from a mold by casting a Cerrosafe bullet?   Seems obvious, but I've never heard of it being done.

I would do a precision layout, but without the correct equipment Cerrosafe should work if you remember the time limits involved with this product. Thermal expansion of mold should be slight unless it's an alum. mold. Do you plan to size, if so add an additional 0.001-0.002 on desired size.

The cheapest way that I know to measure the grooves, is with a tool call a Indi-Cal. they have all kinds of points for them and they work off of a test indicator.You can get extention tips that will measure down to about 1/4 - 5/16. Basically, you set your mic at the dimension you want and then zero the points. They are good for .0005 accuracy or better. Do a search for Indi-Cal and you should be able to find one