I have a difficult time believing that any barrel, old or modern, could withstand proof pressure 9" from the breech.

I gotta call BS on that one.

It would be a pointless test anyway.

Perhaps they have jacked up the loads so as to carry more pressure down barrel, but max pressure at 9"? The pressure there should be 3,000 psi or so, why in hell test it at 6 times that?

How would you even build such a cartridge? With TNT and a 1 millisecond delay fuse?

"The price of good shotgunnery is constant practice" - Fred Kimble