Found nothing new about Manton & Co, but stumbled upon an anecdote about Joe Manton, which I can't help sharing:
When Joe was crossing Hounslow Heath in a chaise late one winter's afternoon, he was stopped by a highwayman. On hearing the summons to "stand and deliver", Manton looked hastily out of the window and recognised a pistol of his own make levelled at his head. "Why damn it, you rascal," cried the indignant gunmaker, "I'm Joe Manton, and that's one of my pistols you've got. How dare you to rob me!"
"Oh! you're Joe Manton, are you?" said the highwayman coolly. "Well, you charged me ten guineas for this brace of pistols, which I call a damned swindle, though I admit they're a good pair of barkers. Now I mean to be quits with you. Hand me over ten guineas, and I'll let you go because you're Joe Manton, though I know you've got fifty pounds at least about you!"
Joseph swallowed his wrath and promptly paid the ten guineas. But he never forgave the highwayman for getting a brace of his best pistols for nix, and he made himself a special double gun, with barrels barely two feet long, which he always carried about with him afterwards when travelling, and christened "The Highwayman's Master". With this weapon I have heard that he subsequently shot a highwayman who stopped his chaise and mortally wounded him.
From "Kings of the Rod, Rifle and Gun" by "Thormanby", London, 1901
