Muzzle diameter is just shy of .800", bore is around .452", of the three I have .452" bullets will drop right thru 2 of them, bullets stops mid bore on the other. Groove diameter is around .458" on all of them, all H&Rs have bore dimensions that are ~.0005" larger at the muzzle than at the chamber end due to not being stress relieved before they're turned to contour.
Tim