A caulk dispensing gun for dispensing a viscous material received in a cartridge, includes a stock having a piston rod, an actuating plate having an aperture for receiving the piston rod, and a trigger pivotally secured to the stock and having an actuating pin for engaging with the actuating plate. The actuating plate may move the piston rod incrementally and forwardly relative to the stock to force the viscous material out of the cartridge. An adjusting device may adjust the inclination of the actuating plate relative to the piston rod, to adjust a frictional engagement between the actuating plate and the piston rod, particularly after the piston rod and the actuating plate have been worn out after use.