I use the MTM plastic rifle rest thing. I pull the upper off and position it in such a way that the front of the barrel hangs low and off the table, and have an old drip pan to sit beneath it beside the bench. Works good.
I have a FAL, which like the AR breaks open shotgun style.
Because of this & the depth of the mag-well side plate wall & pistol grip I like the "Tipton Best Gun Vice". It has more adjustments & an "extra" support that cradles the broken open rifle just at the pivot point. Then the butt & forend can be adjusted to hold rigidly & muzzle down for cleaning.
Last year, I cashed in some of my Cabela's points and bought a HySkore, simular to this one. I remember that the cost was very reasonable and this one could be used for handguns as well. One some handguns, I use it like a Ransom Rest. I not only use it as a cleaning station but to mount scope and sight in. I set it on a clamped table open up my shop door and point it at a target that I put on my neighbor's house.
Not really !! ...