Just make sure you know the actual diameter needed by slugging and go a bit bigger.
For a regular .308 groove diameter, I start at .310 and try .311, usually one or both work
great - but these are conventional rifling. I have not worked with microgrooves, but reading
says make the boolits fit is key, - and it is key to conventional rifling, so I'm not surprised.
IIRC most problems with cast in mg rifled bbls was undersized boolits.
Bill