Miller, I tried a longer post but got some sort of "internal server error" that ate it. Shorter version: American Rifleman article, 1931, "Standard Shotgun Pressure Barrels": describes the crusher method and shows the barrels in use by everyone in the industry. All crusher. As for the Brits, they were still using crushers at the time they switched from the "tons" proofmarks" to bars, in the 1980's. Confirmed this with the Birmingham Proofhouse when I misinterpreted the 850 bar proof pressure as being a transducer value. No, they told me. That's a crusher value. They converted to transducers in the early to mid-90's, but kept the same crusher-derived 850 bar proofmark. Another attempt on the part of those perfidious Brits to confuse us.
