I believe the US Army needs a happy medium between the M-4 carbine and the full size M-16.

Maybe the solution is a bullpup in 6.5mm to replace all carbines and all full sized assault rifles.

The US military is looking for an intermediate caliber between 5.56mm and 7.62mm. Also bullpups give you the advantage of compact size without cutting barrel length. Our solders are facing more indoor and outdoor urban combat so compactness is fast becoming increasingly vital.

I favor the 6.5mm Grendel round because of its better long distance range ballistics verses 6.8mm SPC.

The AR-15 design commits the sin of compromise and pays for that sin dearly, when it is used as anything other then a full sized assault rifle. The AR-15 turns into a mechanical failure of mediocrity when tailored to other roles that are better suited to specifically designed firearms.

When you need a compact rifle that is AR-15 derived the barrel length is cut to carbine length or worst of all PDW size, which obviously decreases accuracy. When the AR-15 is sniperized using 5.56mm, the round itself becomes a limitation when the use is switched from DMR mode of fire to Sniper.

Civilian competition race AR-15s like the ones you see in IDPA 3 gun competition have too much weight and are too cumbersome to be used for anything outside professional competition.