Grunger
I was inspired by a discussion here few months ago under a post when someone glued their plunger rubber part to the bottom their grinder. What if you could just mount it? Meet a milled part for Chestnut C3s pro. I've made this prototype and it functions quite well. I can now leave the plunger part of AP at home, put the grinder inside of the outer tube and save on the backpack space. I'm using it for a couple of weeks now and have zero problems.
What I was worried the most is that it's not to comfortable to be pressing with your hand on the grinder, but not at all. It's even a bit easier as the heft of the grinder requires you to press with less force. Also surprisingly, when using this to plug the AP before pushing down, it tilts but far from being able to topple the whole setup. Nonetheless I usually plug just with the cup part and attach the rest of the grinder for the pushing itself.
I actually made four of them as it was a minimal order and wanted to test few anode coatings. If you're based somewhere in EU I could sell two of them, just dm me if interested. If you were to make one for yourself I'm happy to share the model with you. Obviously to make it compatible with another grinder the threading/attachment and diameter would have to be adjusted. One nice thing about this one is the insides of the cup where the sides connect to the bottom is beveled and it makes getting the grounds out easier than right angles.
Tell me what you think and happy grunging!