It is also noted that the British loaded "Low Velocity" with 1 oz of shot with pressures no higher than the standard 1 1/8 oz load which were suitable for use in a 1 1/8 oz proofed gun. Confusion over this was one of the reasons for changing from the shot weight to Tons proof. The old 1 1/8 oz proof was essentially the same as the later 3 ton proof I believe. The actual shot charge weight is not the important factor, but rather the Pressure of the load.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra