I just got this idea a couple days ago talking to Jammy. Here's a crash course physics lesson:
When a larger object (a pin in this case) hits a smaller object (ammo in this case), only enough energy to make the ammo fly faster is transferred. This is because it takes less energy to make something of less mass move at the same speed as something with more mass. So as soon as enough energy is lost in the pin and gained in the ammo, they fall out of contact and the rest of the energy in the pin is wasted.
You can't really make pins any more efficient than they already are, so I figured I'd try utilizing the otherwise wasted energy. I figured one of the ways you could do this is by making a gun that automatically chambers a round after being fired. It'd be like a bolt action weapon except instead of manually operating a bolt handle, the extra energy would load the the round for you. The result is less effort and more efficient pin use. People may think this is less reliable than manually operating the bolt bin, but I beg to differ. This, in theory, would provide a more consistent chambering action. As long as it's fine tuned, the rounds should load exactly the same each shot. Also, you wouldn't be able to screw up chambering an extra round. You can pull the bolt handle back on a cocked bolt action weapon and easily jam the mechanism. With my concept, you can only chamber a round after the currently chambered one is fired (unless you purposely fiddle with the back of the gun) because the bolt pin relies on the firing pin to operate.

I have the front of this gun finished, but I still need to design the bolt pin assembly and the back of the gun to hold it so that I can actually fire this thing, but I'm confident it'll work out very well once I do. Here's a video to demonstrate the concept.

I'm hoping that once this gun is finished, it'll be a viable war weapon, seeing how I don't have anything better than my Oodassault at the moment. Or at least if I can't finish mine, someone else can use the concept.