A gun for dispensing a fluid from a fluid dispenser has a body portion, a plunger assembly and an advancing mechanism. The body portion has a jaw portion for holding the fluid dispenser in a retained position and adapted for releasing the fluid dispenser when a specific pressure is reached in the chamber of the fluid dispenser. The body portion has a catcher portion for catching the fluid dispenser in a caught position upon being released by the jaw portion. The jaw portion has a pair of legs projecting from the body portion. Each leg has a foot projecting inwardly towards each other and spaced from the body portions, therein defining a flange receiving space. The feet are of such a length to overlie and engage a portion of a flange element of the fluid dispenser. The catcher has a pair of parallel plates; each plate has an opening for receiving the flange of the fluid dispenser in both the retained position and the caught position. The plunger assembly has a plunger rod slideably carried by the body portion. The plunger rod has a plunger element at one end adapted to engage a piston element of the fluid dispenser for moving the piston element towards a nozzle of the fluid dispenser. The advancing mechanism is pivotably carried by the body portion for advancing the plunger assembly in the fluid dispenser towards the nozzle.