Manual Application Gun is required for all Plexus 380 ml cartridges. The plunger for the gun works on a hydraulic action, and creates a smoother flow than most caulking guns. The gun forces out the two components of the adhesive in the proper 10 to 1 ratio. With the use of the mixing nozzle, the A and B mixes and gets dispensed properly. To open up the plunger in order to place in the cartridge, simply push out on the handle.