Some other things I forgot to put on the first list:

How about round storage? Anything but a box full of bullets pushed up by a spring. Maybe taped together? Stored under the barrel, side to side, fed from within the stock, or what? Assembled before firing?

Pneumatic recoil buffers for recoilless rifles? (They are starting to do this with some shotguns stocks.)

Long distance electrical shock delivery? (Like a tazer, but good to 100 yards?)

Gotta have something to occupy the mind until next season....

Chubber