Based on my experience with other models check these things :
- det pin is properly aligned. If pin or mounting inside the slide are crooked, cartridges get stuck.
- det pin has not "swelled" due to its hammering on cartridge piston. Tip of the pin might increased in diameter slightly, causing blockage.
- hole in the cartridges are not deformed. If cartridges hit something when they fall, the may no longer be circular and jam.
Clearances is quite tight, so even minor damage can cause problems.
Another thing is to see if det pin is completely clean of deposits and rust, but I suppose you have this one well in control :-)