I have welded a hole in a set of damascus barrels for a member here. The hole was less than 1/16" diameter. It was about 6" from the breach end. I ran an argon purge through the barrels and and used used a 3/32" diameter mild steel filler rod to plug the hole. I did not use a mandrill or heat sink. Using a large diameter filler rod you basically melt the rod first with it laying right on the barrel. As the rod reaches the melting point the barrel wall is so thin that it reaches melt also and the drop of weld just falls into place. If you get off the pedal quickly. The weld only takes a few second. You could touch the barrel with a bare hand a second or two later. It left a small dimple on the inside that needed to be polished down using fine emery on a wooden dowel. The barrels had plenty of wall thickness and after honing, which was done by the owner I am sure the weld was undetectable. Polishing the OD was a 5 minute job. I don't like using a plug for this type of repair. No matter what material you use some of the plug material will purge into the weld and that is no good. You are bound to end up with a weld that is not 100% filled or with porosity in the surface or both. With the argon purge you do have a small dimple on the ID but the weld is clean and 100%. As for the barrel described the hole is deep and the clean-up will be more difficult. And the bigger the hole the bigger the dimple. Also any type of heat sink is drawing heat away from the weld. When you are trying to weld fast and not cause a lot of heat drawing the heat away can be more trouble than it is a help. And if the mandrill is tight to the barrel any purge would be useless as it would sealed off from the weld area. If it were to get stuck it could be a disaster. If someone were going to try using a plug I'd take the time to make something that is collapsible.
Bill G.
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