If we're talking waterfowl loads, then likely large size steel (4 or bigger) was used. In the case of the Cashmore, unless it has a high performance/magnum proof (1200 bars), then according to CIP guidance on steel used in guns proofed under their standards, American 4's slightly exceed the maximum size limit. CIP-approved steel loads for CIP standard proof shotguns are limited to British 4's maximum--which are just a bit larger than American 5's.
As for the "modern" loads in American guns that came with original short chambers, even if built to shoot smokeless . . . it's a pressure issue, the modern loads developing about 1,000 psi more (at max service pressure) than the previous loads in short hulls. I don't know how many guns were destroyed from a steady diet of overpressure loads, but I'd guess quite a few ended up shooting loose quicker than they would have if fed the proper ammo diet.
Last edited by L. Brown; 07/18/11 04:41 PM.
