A paintball gun assembly comprises a casing having a barrel and a bolt moveable in the barrel to select and fire paintballs. There are located in the casing under the barrel in a linear array generally parallel with the barrel a low pressure regulator, a chamber for air under pressure, a spool valve, a poppet valve, a solenoid and a battery. The spool valve comprises an elongated housing of circular section in which a spool is reciprocable to move seals on the spool relative to radial openings of the housing. The valve has an input opening at one end of the spool and the spool has a longitudinal bore to communicate said input opening with the periphery of the spool at a position between an adjacent pair of said seals.