I haven't been able to get to the range today to test the latest mods. But here's pics...
There's a 2rd mag inserted into the mag well, for carry (plus the 5rd contents of the cylinder!). The mag feeds only once an empty chamber rotates in front of the mag. Once that mag is dry one of the 9rd foot-long mags can be swapped in, feeding from that immediately. You can see one of the long mags at the lower left. The mags clip in via a flat-spring driving a wedge into the side of the mag well; in the long mags, the wedge also doubles as a round stopper. On insertion you peel the flat-spring outwards, drive the mag in, release the wedge into the mag well's retaining hole.
The flat springs are hacksaw blades with the teeth ground off and smoothed.
Surprisingly, the 2rd mag doesn't get in the way at all for carry.