I read somewhere the aluminum was ok for semi auto, but if you had full auto you definitely wanted to the steel. The article mentioned movement,not erosion, if that helps. From a durability standpoint, I would think steel would be better. If you ahve set screws in the bottom, I have seen some manufacturers drill a dimple into the barrel that way the set screw would not allow the block to twist or slide. You might also condier roughing the smooth surface of the barrel under the original FSB. If it is already parkerized you ar eprobably ok with that - the theory being that the rough surface will help with friction and hopefully eliminate twist or sliding.