What type of welding is used on guns?

I am a proficient welder/machinist (actually, I'm good... really, good...), and can tell you, that welding anything on a gun is both difficult and risky. It is very easy to screw up tolerances due to warpage from heat. It also can screw up heat-treat on receivers/barrels, in which can make things really dangerous, really fast. Black powder barrels, especially the thicker octagonal barrels are hard to screw up though unless you are a complete idiot (in which you shouldn't be around anything resembling a gun in the first place). Double barreled shotguns are usually tack welded by the breech (chamber) and then a very fine bead of silver-solder or such is run down the length of the barrel (after measures are taken to ensure "trueness" of both barrels to one another). Usually Tig welding is used to replace metal where it has been foolishly removed (feed ramps, etc.). I have done quite a bit of this, and yes, if you were skilled enough, you could indeed weld two of the heavy octagonal black powder barrels together, providing you could square up each barrel and regulate them. It's a pain though... SM pretty much summed it up. He too knows what he is talking about, especially the risks associated with such work.

On the older double-barreled shot guns, the barrels are silver-soldered together, as are the sights on the old Colt single action revolvers.

As some of the others have stated, welding on any part of the gun, if not done properly by someone who knows what they are doing is very risky, as the heat from welding can warp or distort the barrel, resulting in a very dangerous situation.

I do firearms restoration in my shop, the only welding I do is TIG; this is for adding a sight mount, reattaching sling lugs, repairing sheared bolt handles, or on a couple of occasions I had to reweld a couple of side by side shotguns and a double rifle. I NEVER fill weld a firearm part, if a part is worn or a piece is gouged or broken off I will make a new part. Anytime you try to weld on a firearm or its components you run the risk of affecting the firearms temper. On some old Japanese service rifles I will use a oxyacetylene rig to curve a bolt handle. Unless your very skilled at welding you run the risk of not only damaging a firearm but of causing bodily injury to the shooter if your repair fails.

Guns are not really welded together. Parts are usually machined like that whole and put together with screws and rivets. I can't think of any gun I own or any of my freinds do that is welded together.

Sm is right on........you need equipment and skills which includes experience.