What's the timeframe on your Roberts? What do the shells look like?
This is early to mid 1830s. It follows his 1831 patent but is the later style he made that starts showing up in literature around 1834.
It took a paper shell with a heavier cardboard/wood bottom that a tube primer stuck out of. The underhammers would then smash the tube.
I picture one of them here:
https://aaronnewcomer.com/journal-des-armes-speciales-and-the-battle-of-robert-vs-lefaucheux/Wasn't there a french maker named "Pauly" who had a similar design?
And yes, Robert heavily pulls from Pauly's design and there were even lawsuits between him and makers of Pauly guns (after the Pauly patent had expired). Robert actually made comments about Lefaucheux's guns during one of these proceedings saying something along the lines of: "The Lefaucheux gun had a complicated system that lends itself to bursting open and launching the cartridge into the shooter's face, if the closure piece is damaged missing."
Lefaucheux and other gunmakers of the day took offense to this characterization and responded with:
Dear Editor,
According to the Gazette des Tribunaux of yesterday, Mr. Robert staging, in a trial which is personal to him, the gun who bears my name, would have claimed that in the event of a break of one of the two screws beyond the rocker, this weapon offered dangers of which he made a frightening picture. Allow me to invoke against this assertion, at least inaccurate, the testimony recorded in all the newspapers in the months of April and May last, of the experiments made at Renette shooting, then at Rouen and Le Havre, and in which the hinge screw and that of action were successively and deliberately removed or broken, without the firing of the weapon having even been disturbed. Moreover, Sir, to put the public in a position to to judge in full knowledge of the rifle-Robert and the rifle Lefaucheux, I have just proposed to Mr. Robert, in my name and in that of Mr. Baucheron-Permet, Prelat, Lefaure, Delebourse and Deboubert, all well-known arquebusiers in Paris, a public and comparative test of the two systems, results which we accept as judges the very members of the Academy of Industry who conferred on M. Robert a gold medal.
This challenge and its 70 pages of results is then documented in the book that I linked just above!
Journal Des Armes Spéciales and the Battle of Robert vs LefaucheuxLess than a year later Lefaucheux would patent the pinfire cartridge to work with this new breech-loading design of his and as history shows would clearly become the winner.