I just got round to having another look at my reprint of G.T. Teasdale-Buckell’s “Experts on Guns and Shooting” 1900.
Writing of Cogswell and Harrison’s highly mechanised factory he says they “charge 59gs. for their best gun, but they have met a want with a cheap gun, every part of which except the tubes, is manufactured in Gillingham Street. Close to Victoria Station.”.
I take that to mean they would have machined the pair of tubes (sourced from specialist suppliers) and the lump, joining them into the barrel assembly.
He observes “It enables Cogswell and Harrison to sell a sound London-made hammerless ejector gun for 15gs.”
That would be their boxlock ejector gun, the Avant Tout.