An important part of welding/brazing/soldering on guns is to learn how to protect adjacent areas from heat. That is necessary both for cosmetic reasons and to prevent destruction of existing heat treatment.
In the old days, gunsmiths would not care about ruined bluing, counting on doing a reblue job when the job was done. But with the many restrictions on doing bluing, most smiths don't do it any more and the specialty shops that do charge high prices. (And no, the latest and grreatest paint won't make the owner of a high dollar shotgun happy!)