I added a nice little lock for the cartridge holder cover. Now you only need to pull a lever back and opening/closing can be done without having to fear that all cartridges fall out. I did so many small changes to the locking mechanic that it ultimately resulted in a completely new version. Now you just need to pull two little nubs back and you can open the barrel. Closing is done is the same way. It uses the same principle as the cartridge holder, so it's (int theory) quite stable. The problem is that Lego isn't everything and that it was really complicated to figure out a construct that works for more than just a few openings until it breaks itself. It's an annoying position where most of the forces need to flow into the chamber frames: right over the collision point for hammer and cartridge. My cartridges need a T-shaped space above them trigger the shot which's just not that availabe. So I need to replan a rebuild the lock, probably resulting a rail-like structure above the chambers/trigger component. Originally, I planned to not attach a rail to this one but design one for the next model (which will rather work like a revolver without any breaking). So since I can't avoid putting such a thing on it, it can't harm to design it like a rail and not like a fix. This also enables me have proper sights or mount a scope if I get some appropriate lenses later. It seems that I only need two of them to create a galilean telescope and a couple more for a kepler telescope. So adding a rail on top is probably a good idea since I can then also mount dfferent scope for all kinds of distances and share them across several models. Oh and adding something to adjust the height may also be useful there. Let's see with what I'll be able to come up with. However, this locking really kills me. Never underestimate it's required heavyness when it comes to many connected parts - otherwise it might require rework over and over again.