A4 & M4

Similar Length, Similar Weight.
Colt AR15A4 with a KAC M5 RAS and a Trijicon TA31RCO-A4.
M4A1 SOCOM barreled carbine with a KAC M4 RAS, Surefire 762 SOCOM Mini, and a Trijicon TA31RCO-M4.