You need special equipment to measure a 5 groove bore. Best thing to try is slug the bore and see if it fits into the throats. If it doesnt fit, then you may have a problem.

A gas check design can fix a leading problem. I would try that before reaming. Lots of good info at Cast Boolits website.

Lead Bullet Technologies makes good slugs for checking throat and barrel diameters. You dont have to beat it into the bore.