I have one source that gives essentially the same numbers Miller listed under the previous "tons" markings. But I have another one that states that the "tons" values convert to the current CIP system (bars). In other words, the markings changed, but the proof and service pressures did not. In that case, 3 tons represents the service pressure for a gun with an 850 bar proof, and those numbers--straight from the Birmingham Proof House--are 10,730 psi service pressure, 13,920 psi proof pressure. That would make a 900 bar gun capable of handling the SAAMI standard 12ga pressure of 11,500 psi.
We're still falling a bit short of speaking the same language as our cousins across the Pond.
