The newer Kirsts (at least for the Colt-clones) is avaliable with a loading gate. Still have to grind that big recess in the recoil shield, but the loading gate works like any other, and nothing can fall out.
For the ones without the gate, the unfired rounds can fall out of that loading slot...but it isn't common. Usually load with 5 rounds, with an empty under the hammer. This puts the two rounds on the right side out of line with the loading slot so they can't fall out. When you cock it for your first shot, the last round in the cylinder does rotate past that slot..when the gun gets to full cock, it's past the slot and can't fall out. BUT it could fall out if you were pointing the gun up when you cocked it for the first shot.
After the first shot, the empty cases still rotate past that slot with each cylce...but they rotate past quickly, are expanded for firing , and come to rest on either side of the slot.
I'd still not cock the gun pointed up.
Nothing to stop you from putting the percussion cylinder back in...do it with mine. However, if you have ground that big slot for loading cartridges with the Kirst, it looks kind of goofy in percussion, but it sure is easy to cap.
Also notice that the price has increased in the last year. the pice of the gun + the price of the conversion sylinder comes t to a pretty penny...consider the "open top" offerings.