A gun soldering iron is a power tool, similar in shape to a gun, for soldering conductors using tin-based "Solder (material)" soft solder to achieve a strong mechanical bond with good electrical contact. The tool has a trigger switch so it can be easily operated with one hand. The gun welder is useful when soldered joints must be made intermittently. A constant heat device should be placed in a safe location when turned on but not in use, to prevent damage or injury. The gun cools down quickly enough that it can be set down for a few seconds after use.[1]​.

The body of the tool contains a transformer with a primary winding connected to the mains when the trigger is pressed, and a thick copper single-turn secondary winding with very low resistance. A solder tip, made from a loop of thinner copper wire, is secured to the secondary end of the transformer by screws, completing the secondary circuit. When the primary of the transformer is activated, several hundred amperes of current flow through the secondary and heat the copper tip very quickly. Since the tip has a much higher resistance than the rest of the copper tubular winding, the tip gets very hot while the rest of the secondary heats up at a much slower rate. An additional secondary winding is often used to power a pilot lamp that illuminates the workpiece.[2]​.

Gun soldering irons are used when you need an instantaneous amount of heat that lower wattage soldering irons cannot provide. They are intended to be used for electrical connections, mounting leaded stained glass, and light sheet metal work. A typical gun soldering iron has a power rating of 100 to 240 watts, sometimes it may include a two-stage trigger to provide two levels of heat. Tips designed for cutting and shaping plastic are available; Gun soldering irons for home use can be supplied with a kit of different tips.[3]​.

The temperature of the soldering tip is regulated manually by holding the button until the solder melts and then releasing it. When the solder is about to start solidifying, the button is pressed again, and so on. An experienced worker develops the ability to regulate the temperature as needed. Because the tip temperature is not automatically regulated, using a soldering iron gun for soldering printed circuit boards can generate too much heat at the joint, damaging the board.[3]​.