I read the fingertrap as being "allright, pure double action breaks, make it DA/SA"
Anyhow, designs.
Johnstone's Hexahorse
Calvary on the modern battlefield have two main problems; they are overly fragile against massed fire and they lack the firepower to dispersed formations of well drilled men. To solve this(as well as to reduce the expense and supply problems of having large bodies of trained calvary horses), Edward G. Johnstone has developed the Hexahorse, a hexipedal combat unit crewed by two troopers and equipped with a variation upon the Fingertrap Carbine.
The Hexahorse is armored to resist point-blank rifle fire and is armed with a Armeater double revolving rifle(based upon the Fingertrap)mounted within a open-topped turret; the Armeater essentially being a pair of Fingertraps(with their... mechanical problems properly disposed of) mated together with common trigger(operating one and then the other action) and utilizing chains of chambers(planned to be some 30 chambers in a chain) as opposed to five-shot cylinders. Replacing the chamber-chains in the weapons is possible, if an involved process that is best done in a lull of fighting.
Power to the Hexahorse is provided by a pair of compressed-air engines on a common drive train, powered by high-pressure air stored in a number of air flasks distributed around the vessel. Johnstone has also proposed a "Charger" variant of the Hexahorse mounting a steam core and air compressors which might refill the air flasks. although this is unlikley to be funded at this time.
Rumor has it that the Archer Gun is designed to replace the Armeater within the Hexahorse's turret.
Archer Gun
Inspired by the Fingertrap and the proposed automatic gun port, George Hurbert Archer has designed the Archer Gun for our glorious Empire. The Archer Gun is designed around two systems driven by pneumatic power: a "chamber-chain" of small pre-loaded chambers(including percussion caps) and multiple barrels and actions with loading being done in stages. With just the press of a button the firearm operates; with one barrel "setting" a chamber off the chain into its breach, the second rotating up into the firing position and firing, and the third removing a spent chamber from its breach and setting it back on the chain, the chain thus leading into a container for future reloading or into a small automated reloading press, depending on where the Archer Gun is located. This reloading press(or in positions without the reloader, the simple expedient of linking sections of chamber-chain together) allows the Archer Gun to sustain its fire against our foes of, effectively, forever. The crew will wear out prior to the gun, and the gun prior to running out of supplies for reloading.
Truly, the model of modern military engineering, combining firearms and assembly lines. It has even been designed to effortlessly mount within the turret of the Hexahorse, should one be inclined. As a breach-loader, it is even rifled, and the projectiles are far superior to simple balls!
-edit-
Turns out the cartridges are still paper and in two parts(projectile and propellant and the cap), so edits where required.
Initally, this was gonna use reloadable chambers, but, well, we allready have cartridges, so lets skip that.Oh, why pneumatic and not Steam? Steam aint storable.