Good question, I've wondered about that too.  While I have no experience doing it, I was thinking you could pre-heat the barrel, then TIG weld each hole (TIG for minimal heat). Then set the barrel is a surface grinder to grind the welds down to within .005" of the barrel surface, then draw file to flush and polish. This is assuming it is an octagon barrel. 

My method is to fill holes by not ever using premade screws. They never fit tight enough to not see the fit to the hole. I was taught to thread rod from mild steel rod, and stop the threads short so the threaded rod stops by the threads, not by bottoming in the hole. Then cut the rod off above the barrel and peen the end of the rod. After that I draw file the end and draw flat polish the whole barrel prior to rust bluing. Can't ever hot blue them as that will really show any difference in alloys between barrel and plug.
For extra dovetails I cut my own fillers and make them as tight as possible, and drive them into the dovetails. I leave a small amount protruding out each side of the dovetail, and use two hammers to peen the ends. One on the opposite end to hold the filler while I peen the other end, and switch to do both ends. Once they're filled and peened I draw file to match and polish the whole barrel.
I've got 3-4 barrels on guns in my collection I've restored the barrels on, and unless I point out the fillers for dovetails and holes, nobody notices them.
I would never ever do any kind of welding on a barrel, regardless of how it's done, unless the plan was to line the bore later. It will change the bore when you weld on the barrel, no matter how careful or good the welder is.

The only time to weld on a barrel is when there will be a liner installed after the welding.All welds shrink and can leave a tight spot on the bore. The hammer forged pin idea is good and if you use the same type of metal the barrel is made of it will blue the same.

Here's pictures of the process.  I had to fill a scope hole in the receiver ring of a high wall today.

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I have been able to make holes disappear. However, using a fine glass beading prior to bluing, if the plug and the barrel were not the same 'hardness', they would reappear.

The issue with any plugged hole is how it looks after the finish is applied. If it's a color cased receiver they'll be nearly impossible to find. If it's a rust blued barrel they will show, but will be very hard to see. I find that polishing over the plug with whatever grit paper you use will still give a different finish once the area is rust blued. And if anyone decides to hot blue the barrel the colors will really jump out and show well.

JLouis wrote on Feb 28^th, 2023 at 1:56pm:


Yes, if it's a new barrel, and you had a stub leftover to make plugs. But if it's a new barrel, then likely wont need holes filled.
Not knowing what the exact alloy is, or how hard each barrel or receiver is, is the issue. And I don't know short of testing how to figure that out. So tough to make it from the same material when it's an unknown.