Custom/Match service rod
Harold: Give this some thought; Both the Service and the Match rod can ride the lands [bore] only of the barrel which are/is narrower than the grooves. The chamber mouths are (generally) no more than .001-.002 larger than the grooves to allow for lead/cast bullets to clear the chamber mouths without swaging down narrower than the groove diameter of the barrel.
Since the rod cannot be any wider than the lands/bore, it will not be as wide as the grooves and will always have some clearance at the chambers' mouths. Unless there is some serious play in the cylinder timing the rod will never touch the cylinder mouth.
Given that your GP100 and SP101 will shoot .357 dia. bullets and the rifling will be .002"-.003" deep avg.,- if not more- the rod will be a least .005-.006" narrower than the mouths, unless the rod is tight enough in the bore so as to have absolutely no play whatsoever. If either rod hits the chamber mouths while checking, you might have second thoughts about shooting either gun in that condition.
This was explained to me by a local 'Smith who worked on both my GP100 and Mod 65 Smith.
As long as accuracy is good and there's no lead spitting from the cylinder gap, everything should be okay....Quit worrying over nothing and tear up some targets.
WILL.
