The normal way to make the determination is to slug the barrel. This involves taking a pure lead ball, cast bullet, or fishing sinker that is a little wider than the bore, running an oily patch down the clean bore, then using a wood dowel or brass punch to hammer the slug into the muzzle and a cleaning rod to push it through and out the breech end. The lead ball is then measured across the groove marks with a micrometer to determine bullet size.
I don't know what tolerances the Czechs were working with, but in WWII, the U.S. tolerance for barrels was ±0.0015 inches for both groove and bore, so measuring is the only way to know exactly.
I don't know what tolerances the Czechs were working with, but in WWII, the U.S. tolerance for barrels was ±0.0015 inches for both groove and bore, so measuring is the only way to know exactly.