Long gun disarms are easier than taking a pistol from someone as long as the muzzle is as close as I'd make a handgun disarm at the start of the party.What about an AR-style rifle at 3 feet? Like this:
Sweep the muzzle off line, and MOVE INTO them, the long arm is useless. They'll try to gain some distance in an attempt to get the muzzle back onto your person [ don't let them by denying them that distance they need to do so. That's where the H2h training would come into play.