fictitious war...pick your arms

[LRRPF52]

Not knowing any other parameters as Stan mentioned, the large frame guns are automatically off the list since they suck at riflemen tasks for the close fight, and disallow you from carrying a basic load that can last more than 2-3 realistic bases of fire, while weighing you down excessively. Clearing rooms with 7.62 NATO will rock your skull into new meanings of overpressure, if you haven't tried it yet. Even an AK will disorient you in the house without good protection. You can go have a professional boxer glove up with light mitts and beat your face repeatedly for about the same effect.

I would go 14.5" Grendel with 1/7.5" twist, suppressed with a dedicated reflex-type can that doesn't backblast into the bore, so overall length of the carbine would not be much over a standard M4 profile.

Slim & lightweight handguard with dedicated 12 o'clock rail, integral QD sockets up front for sling.

Electro-Optics I won't elaborate on.

This system would cover contact distance CQB out to 1000m/1100yds, in a 6lb gun without even trying to make the receivers lighter, normal barrel profile, nothing crazy. If you wanted to lighten it up, you could really shed some weight, as the Electro-Optical system would add at least 1.5lbs.