think it would work best with the action held open untill your out of the water, than release the bolt and begin the fun. I dont think that a .22 inch diameter rifled tube of 14-20 inches will drain well if one end is clogged. However with the bolt open the barrel and gas tube should drain pretty quick. Im not sure what it is that makes the AR-15 unable to fire wet though. If it is water in the gas system, barrel, or bolt/gas seals that is dangerous. But slappin the bolt shut oughta shake some water off too.

Doing either probably isn't too safe, whenever I've seen videos of an AR-15 being fired wet, the firer drops the mag and works the action about 5 times before reloading and firing.

AK's fire underwater, right?