67mm Shell Lengths
To those of us in the USA, the 67mm shell length for shotshells is a mystery and virtually unknown. Even more unknown are the problems created by not using it in some semi-automatic shotguns. Our standard shell length in the USA is 2-3/4 inches or 70mm. Standard long magnum length is 3 inches.
One may notice that the 3mm difference from 67mm to 70mm is negligible, indeed it is negligible on paper, and in theory the 70mm or 2-3/4” shell length shouldn’t matter much to a shotgun, after all it hasn’t a brain. But it does to some, and all of them are European made semi-automatics.
While it is perfectly safe to fire standard 2-3/4 inch shells in all European semi-autos and other European shotgun action types with 67mm chambers, the semi-automatics don’t always cycle reliably with the 2-3/4 inch shells. Most gun owners simply believe they have an overly finicky shotgun, some may even believe they own an inferior firearm.
The 67mm shell length will cure those problems for the European semi-autos. 67mm shell lengths apply to 12ga., 16ga., and 20ga. only.