I don't know how many stations you have on you press. If you can find an open one,a "Powder Cop Die" might be an option.
On your question " What size should my groove dia be" It is what it is.
The point is to select a cast bullet .001 larger. Gas leakage past the lead bullet is a problem
On your question " What size should my groove dia be" It is what it is.
The point is to select a cast bullet .001 larger. Gas leakage past the lead bullet is a problem