You can also shoot 2 3/4" shells, loaded to appropriate pressures for the gun in question, in a 2 1/2" chambered gun without lengthening the cones. The Brits didn't lengthen cones when they started using longer hulls in the short chambers. All they did was stick with the same recipes they used in short shells.
When you grab off the shelf ammo at the local WalMart (or probably even sporting goods store), you can be OK if you go with the Winchester Low Noise-Low Recoil stuff. But about the time you grab a box of "light" target loads . . . woops, you're probably exceeding the pressure for which the gun was designed. So if you're going to go with factory ammo and not order from someone like RST or Polywad (or Brit or European shells), your off the shelf choices are very limited. It was not that way back before WWII, but back then a very high percentage of the shotguns being used had short chambers. Not true today, unless you're taking your percentage count at the Vintagers or somewhere like that.
I think the safety experts would tell you that most blown shotguns come as a result of some sort of bore obstruction.
