Originally Posted By: Tom Martin
Us guns are usually built to SAAMI specifications, and current SAAMI specs call for a bore diameter of 0.665" with a tolerance of 0.020", so a modern gun could have a bore of .665" to o.685" and still be within industry specs. Having said that, I have always heard that the 16 ga bore diameter was 0.662".


If that tolerance works in both directions, then the bore diameter could be anywhere from .645-.685.