Quote:
In Michael McIntosh's book SHOTGUN TECHNICANA, Chaper 27, it is stated that a 12 gauge with a nominal bore diameter of .729" is out of proof, "unsafe" at .740" there is more to it and it is rather, well...Technical


I can't argue with McIntosh, but do be careful of generalizations when it comes to older guns. A lot of early 12 gauge Parkers came from the factory with bores at .750 or larger. Barrel wall thickness is more important than bore diameter, but much harder to measure accurately.