I wouldn't have thought silver solder would be good for a butt joint like that? Not enough surface area? Remember, it is only a strip 3/16x1/4 that contacts. The gun digest I have that features cooper knives said he arc welded them, nothing more. That leaves a lot of room for speculation. I have heard arc welding to refer to all kinds of electric welding. Even if they used it in the normal sense (stick) that still doesn't narrow it down much. Only about 50,000 different electrode type/diameter/current options.