it seems these days that most warfare involves the troops carrying equipment rather than direct rifle action.  whether it be setting up drones or carrying LAW missiles etc.

i had an idea for a rifle whereby the overal size matches a magpul PDR / FNP90 / Deserttech MDR-c.    basically a length of 18 inches or so

the mag is located right by the buttstock, like the soviet OTB-22.   To feed the rounds, they are pushed forward by a rammer - or perhaps a rising chamber or something

anyway, this gives you a barrel of 16-17 inches in a P90 sized gun. 

for the ammo, it's either a SPC / grendel case containing a .338 sabot and a .204 bullet,  or a non- sabot round.  This would be a 6mm ARC necked up to .25 caliber for better short barrel performance

ME would be 1950ft Lbs

do you think this would work, in terms of reducing the infantry load, so they can carry equipment?

would the unsual action be practical for a modern cartridge?

and would a hot .25 cartridge be able to reach high energies in a 16 inch barrel

Too complicated. Just issue AUGs or an upgraded Kel-Tec RBD.