I do extensive pattern testing with all my shotguns and "generally" factory choke designations, bore measurement at the muzzle and patterns are consistent except for two 20 ga's. One a Red Label purchased from the factory, designated Skt/Skt; measures at the muzzle Skt II/Modified (don't know true bore dia.)shoots with multiple "standard" 7/8oz loads true Cyl. and Full. With extensive testing I have been able to come up with barrel specific loads to give me Imp./Mod. patterns. The second gun, an SKB, came with factory designated Mod./Full chokes. Without pattern testing the barrels were sent off to a "noted" barrel smith to be opened to Imp./Mod. Chokes were honed to desired constriction based upon bore dia. Chokes at the muzzle still measure exactly Mod./Full, which means the bores are both appx. .010" undersize. Pattern testing again with multiple standard loads resulted in Cyl./Full patterns. Coincidentally or not, the same barrel specific loads developed for the Red Label worked in the SKB to give me Imp./Mod. patterns. But why don't the choke measurements and patterns (extreme both ways) match?
