A spray paint gun having a disposable cartridge inserted therein such that paint can flow through the cartridge in the spray gun without touching the spray gun. Since no part of the spray gun has paint touching it, there is no cleaning of the spray gun or its components. The cartridges can be easily inserted into the spray gun and easily removed such that different color paints can be used in the spray gun in quick succession without down time for cleaning. There is no use of solvents for cleaning, making the cartridge spray gun environmentally friendly. The disposable cartridges eliminate expensive time consuming cleaning. The cartridges can be breach loaded into the front portion of a spray gun and front portion containing the cartridge can quickly snapped into place and ready for use by a hinged connection to the rear portion or by other connection means. The cartridge may include an integrally formed or otherwise attached gasket member to perfect an airtight seal at a joint in the air passage leading from the gun's handle portion to its spray nozzle.