Real M16A2 on top with real bayonet. Real M4 barrel is the same length in front of the front sight, 16" carbine barrels stick out farther. Note the M4 barrel is not 14.5" because of any magic or ballistic testing, it's 14.5" merely so the standard bayonet can be used. The original M4 design was specific design for a foreign military who wanted the bayonet (vs the M177-series which won't take a bayonet) and Colt later sold the idea intact to the Army.

No bayonet lug on the M&P15-22 on the bottom, but you might be able to fit one. A reason do do so remains a mystery.



-- Chuck