The Rsh12 is one of only four guns in the game with fully modeled cartridges in the magazine.
The other weapons that model cartridges in the magazine are the M4A1, the M249, and Unica.
When performing a tactical reload, an entire cylinder is dropped rather than the individual rounds one would expect. This inconsistency is likely in place to make it easier to find cylinders so they can be picked up again.