>We reached a brick wall when it comes to engineering weapons, calibers, ergonomics
hardly. Check out this high efficiency propellant that still isn't used, not even caseless ammowww.dtic.mil/cgi-bin/GetTRDoc?AD=ADA433982
the rifles themselves still have a lot of weight to be shaved off. New rifles are coming out that are over 7lb. Now that's not heavy but it's way more than needed - compare it to this guy's 3.6lb AR. No, it's not fully featured, no adjustable stock and rails must be added to the handguard, but it's damn light. A gun built from the ground up should be able to get close with full features.http://subsixtyounces.tumblr.com/
one guy reminded me of grenade launchers. High-low gas systems are ancient in design. There are several patents from the 50s and 60s for extremely slow-burning propellants that would eliminate the weight of the high-low system, and lower pressure so much that lightweight plastic cases can be usedhttps://docs.google.com/viewer?url=patentimages.storage.googleapis.com/pdfs/US3771451.pdf
pair that propellant and lightweight cases with electronic fuses, tada you've cut the weight of your 40mm grenades in half and increased velocity. Don't care about weight? Let's put more explosives where the mechanical fuse used to be, now you have more boom. Add airbursts fuses - holy shit this thing is lethal now.
tl;dr we have a long way to go