It depends upon what sort of condition the crown is in.
If the crown has any deep nicks/gouges, use of a hard tool, to resurface the crown would be indicated prior to lapping the egdes of the rifling grooves for an all-around even exit from the bore.
Sometimes, muzzle damage is significant enough to need either a barrel shortening or a crown recess via an oversize drill bit run 1/8" or so downbore, then the end of the rifling chamfered & lapped/crowned.
The round head brass screw is great for minimal lapping/cleanup - but I've found it best to use several sized screw heads, to reach various parts of the crown for smoothing/lapping.
Remember to plug the bore first with a cotton patch, then push it out from the rear when done.
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