Building for accuracy

[Hoot]

If you have some bee's wax around the house, roll a little shaving into a mouse turd shape. Run a jag into the barrel and looking down through the gas port, line the jag up so that the solid part is right below the gas port. Push the wax plug into the gas port so that it runs into the jag and stops going in any further. Mash it down hard so that it expands to plug the gas port tightly. Remove the jag. Loctite the block in place and once you're satisfied that the Loctite has cured thoroughly, warm the gas block with a heat gun. The wax plug will fall through into the bore. Push it out with a patch. Blow some compressed air down the gas tube from the receiver end to displace any remaining wax and follow it up with some brake cleaner to wash any remaining wax off the surface of the port. Clean the bore as you normally would and you're all set. If, for some reason, there is any remaining wax, the first shot down the barrel will vaporize it. You can also use modeling clay, though it may not fall free when you heat the block. The jet of compressed air while the block is still hot, will displace it.

Hoot

EDIT: I forgot to mention to block the hole in the block that lines up over the port as well. Same method.