When I had the DuraCoat bead blasted off of my .204, I plugged the muzzle with a small piece of aluminum rod that was wrapped with duct tape and I packed the receiver/chamber with a wad of modeling clay that I picked up in the hobby section at Wally World...
I stripped the lower receiver of the butt stock and trigger group, but left all other parts intact..

After the bead blasting, I soaked the parts in a tray full of air agitated mineral oil to work loose any grains of the media and then gave the whole thing a bath of sprayed on alcohol to remove the mineral oil and any media that may be being held to the surface by the oil...
After the weapon was dry, I sprayed it again with a can of Auto Prep to insure that all the oil residue was gone and primed it with a self etching primer..

After that, I painted it as I wanted and it's holding up well...