I made an error in one of my statements above, re the pressure barrels. They were standardized, all made by Winchester, and used by the ammunition companies (at least a couple of which--Winchester and Remington--were also gun manufacturers). It was all about standardization of ammunition velocities and pressures (without, at least per the article, interference from the evil government). And the reason the ammo makers were interested in doing that had to do with making shells that were safe for the guns in which they were to be shot, and also to improve the general performance of their loads. As for the arms makers, the fact that they proofed their barrels can be seen by the proofmarks you'll find on them (as well as reference to the pressures at which the various companies proofed their guns, also from period Rifleman articles) whether it's an Elsie or a Parker or a Winchester 21. And of course there was Olin's famous test, in which he fired a couple thousand proof loads through a 21, comparing its ability to survive the stress of repeated use of proof loads in comparison to Winchester's competitors (all of which also survived dozens of times more proof loads than were generally used in standard proof testing).
Miller makes some good points. Because American shotguns, in general, were overbuilt, it was not necessarily a problem to lengthen the chambers of an American 12ga from 2 5/8" to 2 3/4" and then fire the longer ammunition in those modified guns. (However, it is also worth noting that the American arms companies--again, per Rifleman articles from that period--proofed their short-chambered guns to lower pressures than their long-chambered guns.) But we also know, from discussions on this BB, that in the case of light 20ga guns--especially some Ithaca Flues models--using modern ammunition in those guns, most of which would originally have had 2 1/2" chambers, thus meaning that a full 1/4" of chamber steel would have to be removed if they were lengthened to 2 3/4", has resulted in "catastrophic failures". Especially cracked frames on some Flues 20's. When you lengthen the chambers of a gun that has been proofed for X level of pressure, for the purpose of using ammunition designed for guns proofed for X + something level of pressure, that gun is out of proof. And it is out of proof if it's a Fox or an Elsie, every bit as much as if it's a Scott or a Purdey. The only difference is, we're less likely to know it's out of proof without knowing the original chamber length of the gun in question, when it was made, etc, than we are with a gun sold in a country where it is illegal to sell guns that are no longer in proof. It is, much like the safety on a gun, simply an added (but certainly not foolproof) level of protection for the buyer. Think the law that requires car dealers to disclose the true mileage on a car they sell you. While that does not guarantee that the car won't fall apart shortly after you drive it off the lot, it does guarantee that it only has 50,000 miles and not 150,000 miles. Personally, I think--from the consumer's standpoint--that's a good law. And just as a car with only 50,000 miles can be expected to have more "life" left in it than one with 150,000, so can a shotgun using ammunition appropriate to its level of proof be expected to have a longer life than one fed a steady diet of ammunition with a higher pressure than that for which the gun was built. So while it's not necessarily about danger to the shooter, there's still a very clear consumer protection element involved.
