Hi Sydney,
Following is a post from the archives by the late Don Getz on making a spring clamp for holding a front sight while soldering it in place. I miss Don.
here's a simple little clamp you can make that will make this job a lot easier.
Use a piece of strap steel about 1/2 wide by about 6 long, it should be at least 1/16 thick, or slightly thicker. Bend a 1/2 long leg down at each end. On one end, file a concave radius, equal to the barrel diameter. On the other leg, saw or file a slot that will fit down over the sight blade. After you have the sight base tinned, and have the spot on the barrel cleaned up and fluxed, place this clamp over the sight, and back toward the other end, place a parallel clamp to hold the whole thing in place. There will be plenty of spring pressure on the sight so that when you apply
heat, it will squeeze right down into place. Also, if it doesn't look right at that time, it's so easy to slide the whole thing around the barrel to properly position the sight....make one of these...I've been using one for years.....Don