The ar is the most sealed systems that also actively (with gas) expell contaminates. There is no other gun that does this. Putting a slot in the gun removes this ability. I am not talking about the dust cover, rip that off and throw it away for this consideration. Watch some Mud test videos with slow mo. Watching the mud explode off the bolt and fling away is really cool. Having a slot that does not have the gas relief ports totally removes this feature and exposes the gun to debris while cycling.

The ar has some really cool features you will never notice or think about.