Here’s my annual gift to entrepreneurs: If you want to make money, bring any one of these items to market and I guarantee you success!
More heavy subsonic .22LR ammunition. The market above 40gr is still limited to the Aguila 60gr load!
Gapless revolvers. The Nagant 1895 Revolver goes into battery when cocked to seal the cylinder gap. Revolver manufacturers pride themselves on their lockwork but the biggest innovation in revolvers in the 120 years since the Nagant went into service has probably been the shift of the barrel to the bottom of the cylinder with the Chiappa Rhino line. How about a revolver that is normally in battery and only cams out of battery to open or rotate the cylinder? Eliminating that loud, dangerous gap would be very cool, and doing it with a nice trigger pull would be a worthy achievement for a revolver engineer.
3-mode single/autoloaders. Historically automatic rifles have had a three-mode selector that toggles between Safe, Semi-automatic (one shot per trigger pull), and Automatic (typically either a 3-round burst or continuous fire while the trigger is depressed). For the civilian market that third mode has been eliminated. But there is another mode that would not be restricted that I would appreciate having in its place: Call it Manual, which would fire a loaded round but not cycle the action. The biggest benefit would be found shooting suppressed, where the option of keeping the action locked up would result in quieter shots and less fouling. The Manual mode would also be a useful tool for training. Granted, it is possible to run some piston guns in manual mode: the Ruger SR-556 and the XCR have gas selectors that can close the gas system completely. But they aren’t designed to be easily toggled the way fire control switches are.
Faster, cheaper, higher-resolution video cameras. As of now there is a gap between the $5500 Edgertronic, which can shoot 720p at 700fps and lower resolutions up to 18kfps, and (of all things) the $900 iPhone 6 which maxes out at 240fps in 720p. No camera in the consumer price range offers sustained video above 240fps!