The best information hat I have ever seen on this subject was reported by Major Gerald Burrard in his 3 volume book "The Modern Shotgun". This was thoroughly studied by the British Gunmakers & ammunition loaders well over a half century ago. The studies actually started with the introduction of the fold/pie crimp hull in the late 1930's which resulted in a shorter length of the "loaded" shell than a shell with a roll crimp. They were finalised immediately following WWII prior to the 1950's.
Burrard didn't just depend on what He could "Find Out for Himself" but worked very closely with the Pro's in the field & reported their findings.
Note that if the gun has a step or a short angle rather than a Cone Proper then a shell which opens longer than the chamber length should not be used as the end would then lap up into the bore itself rather than in the cone. This condition is very rarely found & mostly on very old guns.
