Plugs or dowel rods
Brian, I usually use oak dowel rods and then chuck them up in my drill press and turn them down tho a taper using a rasp. I drive them in with a rubber mallet to make sure they are tight. They make plugs out of silicone and the blasting man should have a set of these. Make sure to plug both ends of the barrel. I use sandblasting tape which is close to 1/8" thick to cover anyplaces that I don't want blasted, then man should have this as well. On most guns, I simply remove anything that I don't want blasted such as sights. If I cannot remove them, I apply the spray designed to hold the tape down, let it dry, and then apply the tape. This keeps the tape down where I want it to stay. Plug any holes with a toothpick or dowel rod of the appropiate size and then start to blast. I always like to spot check a place that will not be seen like the grip section of a frame first to make sure I am getting the finish I want. If all is good, then I blast the whole part. When I remove the parts, I wear rubber gloves and then use a high-pressure air hose to blow the parts off first, then I usually go straight to my parking tank. For you, I would suggest blowing off the parts and then using some kind of rust preventative to spray all over the parts and make sure to leave the plugs in place and slide the parts into a plastic bag and tie the bag up removing as much air as you can before tying the bag closed. When you get them home, I would use the rubber gloves to remove them from the bag, and then apply MEK or laquer thinner or Prep to remove the oil you sprayed on them. Do this several times and then rinse off in hot water and watch and see how the parts dry. If the water looks like it just vanishes off, then you're ready, if it hangs on the part for a while, I would do another treatment of the degreaser and then wash it off and blow it off using high pressure air again. The reason I use the oak dowels is so I can use them to suspend the barrels by wire when I paint them. I use stainless wire to hang the other parts. You should be ready to apply the paint now. I didn't ask, but how will you be apply the Gunkote? Make sure you shake the can for the appropriate time the can says to, don't shake it for a minute and say you're ready because the paint has particulate matter that has to be shaken pretty well to mix it into the paint. If you are using an airbrush, I would set the psi to 30 and check on some scrap how the pattern looks. For an air gun, I like to start at around 40psi and work up or down from there. Make sure to keep the right distance from the parts and make smooth even passes. Good luck with the project. Show us some pics when you get it done.
Jeff