Ben, proof would not be applied "retroactively" any more than it was when proofhouses and proofing were first required in European countries. It would apply only to new guns, or to guns undergoing alterations (such as lengthening of chambers) that would require reproof in countries that do have proofhouses.
Right now, we have gunsmiths who solve the "problem" of short-chambered guns by boring them out to 2 3/4", sometimes without marking the new chamber length--or the fact that the gun has been altered. As Buzz pointed out, there are a whole lot of Americans outside of our little clique here who do not realize that the solution to shooting 2 3/4" shells in a 2 1/2" gun is not punching the chamber and then feeding it a steady diet of American factory ammo. I can verify that fact, because long ago and far away, I was part of that group. So there are some reasons why we should do business differently than we now do it. If, after all, the govt is going to license barbers--for example--then should it be all that unreasonable that they also license gunsmiths, or somehow exercise some control over practices which can result in danger to the user of the gun in question? SAAMI works well enough to establish standards for ammunition, and for the proof of new guns by American manufacturers. Where the system falls apart is that nothing happens once a gun has left the factory.
