I've got a couple of shiny stainless barreled ARs that I would like to bead blast to a dull grey. I know nothing about bead blasting, but thought I might screw around with the cheap Harbor Freight gun.

Can I safely do this by taping off the muzzle device, gas block, tube, receiver, etc. and padding the scope? Do I need to fully disassemble the upper? Is there a middle ground?

Is bead blasting easy enough for a first timer to do a decent job with cheap tools?

Remove the barrel entirely. You can leave the gas block on and tape that and the muzzle and breech. Blasting media tends to get everywhere.

I’d disassemble completely.  As said, blasting media gets absolutely everywhere.