Shane-I suspected that the gas ports were probably opened on those 11.5" barrels to compensate for the substantially shorter dwell time. Since the bolt won't get gas for very long, it's gotta get a lot of gas and get moving pretty fast.
Some googling revealed that the port on an 11.5" barrel is 50% larger than on a 16" barrel (from Colt).
So it's still a carbine length, but it's definitely getting more pressure than the other carbine barrels.
