Why so few innovations in the last 40 years?
Well, the potential inventor must have an interest in firearms: ain't gonna get it in school or the Scouts any more; ain't gonna happen in a city or country where private ownership is (all but) prohibited or frowned upon.
Must have some engineering/mechanical experience; ain't gonna happen with today's disposable society. My high school dropped all shop classes a few years ago because Little Johnny couldn't read, much less read blueprints...forget about
creating blueprints!
Must have somewhere convienient to shoot/test; can't just go to the sticks or the back yard without upsetting the neighbors!
AK/FAL/M-16/G-3 and Glock were the last revolution of firearms. Everything else I can think of offhand is evolutionary, due to improvements in materials. G-11 unworkable, for now...
OK, say I invent something totally different that is optimized for an all-new proprietary cartridge - who am I going to sell it to, the "JMB is God" crowd? The ".45ACP vs. 9mm vs. 40S&W" camp? Hunters and Sportsmen? LEO and military only, so ya'll can't buy one anyway? Besides that, the first time a kid or cop gets shot by my invention I get demonized and sued. So, where's the incentive?
Too many variables to solve this equation...