And remember...the solder will always flow toward the highest heat. So, if you are soldering two items of very different sizes (i.e. a barrel and a lug) and you concentrate the heat on the joint, the smaller part will heat first and all the solder will run toward the hottest area of that smaller part. That's why Jerry is suggesting heating from the back side of the joint. When the larger part is hot enough to allow the solder to flow, the smaller part will also be hot enough and, if you have tinned the lug, the solder will flow from the lug toward the barrel. This is true for any solder from low temperature Tix solder to the highest temperature silver solders.