I believe those velocities over 40 yds are US figures. For many years in the US, shotgun velocity was stated this way. The Brits used the observed velocity over 20 yds from way back. This was at times converted to Muzzle Velocity. The early chronographs which marked a dropping rod simply required a longer time interval for accuracy so velocities near the muzzle were not reliable.
Except the pressure readings are shown in tons. Were we using tons for pressure back then? As best I can recall, I always saw US pressure measurements expressed as psi . . . before it was determined that psi wasn't really accurate and they started using LUP/CUP instead for crusher measurements.
And I'd thought that the Brits had dropped the "observed velocity" (avg over 20 yards) measurement . . . except my Eley Shooter's Diary from 2005 still refers to 1070 fps as "standard velocity" and 1120 fps as "high velocity (although they do give the metric equivalents of 325 and 340 meters per second, respectively.) You'd think, since they're in the shotshell business, that they'd be using whatever is the current standard measurement for velocity . . . if there is one.
