A few points. The Bell test was with two Parker doubles of about the same era, the same frame size, one with pitted Damascus barrels and one with fluid steel barrels. At no time was an obstruction used. The ammo was loaded in 2000 psia increments and fired in each barrel. The testing started at about 10,000 psia which was already over the average hunting pressure loads of the early 20th century. These loads increased at 2000 psia increments until failure. That is a LOT of pill loads for old guns. There was no damage until each chamber burst at about 30,000 psia. One barrel went at about 29,500 psia as I remember and the other three in each gun went at by 30,500 psia. The fluid steel failed at the same pressure as the Damascus in each case. This would be as expected as both barrels were designed and proofed for the same loads. Both guns were #2 frames. Both guns also had pressure testing devices on the barrels to back up the precalibrated pill cartridges.

Another test of note. This is a m"me & Joe test" but interesting. A cheap Damascus barreled belgium import shotgun showing its age with extreme use (as most of them had) and very loose was used to show some kids how dangerous it was to carry two different sizes of ammo at one time. A 20 ga shell was slipped down the barrel and a 12 Ga shell loaded in the chamber. the gun was then shot with a string behind a tree. The gun survived two such tests. Hard to believe, but perhaps the extreme looseness had something to do with it.

Modern failures. I know of 6 high grade Italian clay shotguns (of the same manufacturer) which have blown barrels and half with factory loads. There was no evidence of barrel obstruction. An engraver friend has shed some possible light on this. These guns have parts which greatly vary in hardness. The harder they are, the more difficult they are to engrave. It is difficult for him to give an engraving cost estimation as the very hard parts are much harder to engrave and sometimes need air powered engraving like 300,000-500,000 rpm dental tools. These are not meant for working in hardened steel and often require new bearings which is about $300 per. He believes the parts are probably sourced out and the final part only tested for minimum strength by a hardness test. Some materials and hardness tempering causes greater brittleness than others. He believes this may be a reason for the failures. Naturally, the manufacturer wants to blame the ammo.