What diameter for cast boolits?

[Oldman-Winter]

How much bigger than groove diameter should a cast bullet be? For instance, if
the groove diameter is .310 inch, should you size your bullets to .310 inch, or a bit
bigger?

Also, for the 7.62x39 with a .310 inch groove, will .308 cast bullets upset enough
to fill the .310 groove?

[NVcurmudgeon]

I like to size one or two thousandths larger than groove diameter. Depending on alloy, casting temperature, and variation in sizing dies, you have to give and take a little. My somewhat oversize boolits are accurate and leading-free. Probably the BEST way to insure leading is with undersize cast boolits, especially hard ones. If you go too much oversize, you could get into a situation where a loaded round won't chamber. To be sure, slug the throat, then you know for sure what will work.