Here's the problem:
Armalite set out to move the front sight base further forward, to a "mid-length" location, since 16" barrels are required. And that was a fantastic, long-overdue idea.
But THEY SCREWED IT UP!
Intead of maintaining the same distance from the FS to the FSB, allowing bayonets to be used, they designed the upper with the FSB too far forward. Now the barrel (compared to the bayo lug) is 11/16" too short! ARGH!
And, of course, since that was the "mid-length" "standard", that length was copied by RRA (who are former Armalite employees).
So, now, the whole idea of the mid-length 16" barreled rifle is SCREWED.
Sorry, Armalite, you blew it.
-Troy