is a sound suppressor for the anti-material rifle. they are already making them now...as evidenced on the tv show "Sons of Guns", and i think 80 years later they should be commonplace.
also, extended mags for the 21.7 submachinegun.
with a silenced amr for long-range, the 21.7 smg for group throwdowns, and the 21.7 silencer pistol for close-up take-outs is all anyone would ever need.
over-whelming firepower for sneak or stumble-in has always been the key for success.

12.7mm SMG maybe. not 21.7mm

I just want my two front teeth

A 21.7mm SMG

Why not? I'm sure a 40 foot robot could carry and fire one.