If you do a search back about six months or so I posted pictures of how I do it. It's actually pretty simple if you take your time.
Basically, it's nothing more than screwing in threaded annealed blanks, peening them down, and filing/contouring them in. It makes for a literally invisible fix without having to resort to welding them up. When you start filing the joint just disappears right before your eyes.
addition: the topic was covered on 8/20/07 under the title of "Filling a Barrel screw hole."
Last edited by RickB; 02/19/08. Reason: additional info