New Army "Caliber Configuration Study"

[stanc]

If you bullpup or semi-bullpup a smaller LMG, using the best component systems of LMG's to-date, chamber it in something with 6.5mm 130gr at 2500-2600fps, then you really have something.

Indeed it would. I don't know if a belt-fed bullpup (with acceptable ergonomics) is feasible, but the M60 series clearly shows that a semi-bullpup LMG can be done.

I wish I could say the same about your proposed 130gr load. I just don't see how a lead-free 6.5mm bullet heavier than ~110gr can be viable. A 130gr LF Ball projectile would be extremely long, and a matching LF Tracer even longer. Perhaps too long to be practical?