Interesting that this G. Defourny-Sevrin(owner gives Auguste Francotte) sidelock on ShotgunWorld has the phrase "Sir Joseph Whitworth Fluid Pressed Steel":

http://www.shotgunworld.com/bbs/viewtopic.php?f=5&t=399406

Did all Belgian examples with Whitworth have the term "Pressed"?

Kind Regards,

Raimey
rse