A paintball marker, also known as a gun or a paint gun, is the main tool used by players to mark their targets in the sport of paintball. The marker is powered by a compressed gas, usually carbon dioxide, although some markers use high-pressure air (HPA), industrial nitrogen or other gases. The marker is loaded with paintballs in a loader or hopper, and the mechanism of the marker fires the paintballs through the barrel.

Some markers use a stacked tube design, with the bolt and valve in separate tubes; to fire the marker, a cycling hammer or ram must strike a pin valve inside the valve chamber and open the valve to allow compressed air to flow from the reservoir through the powertube and into the bolt to propel it forward. Others, such as the Nelson valve marker 007, employ a “balanced spool valve” design that integrates the bolt and valve into one component, eliminating the need for a separate valve and allowing a smaller, more compact marker. The marker is cocked by pulling the trigger, which disengages the sear and releases the hammer against the force of the main spring. This opens the valve, causing compressed air to flow from the reservoir through the bolt and powertube to propel the loaded paintball forward, then closes the valve with the hammer against the force of the sear. The marker is then ready to fire again.

The body of the marker contains the major components of the firing mechanism, as well as the marker’s electronics and battery. The body also holds the marker’s air tank, which is filled with either carbon dioxide, typically in 12 gram powerlets, or HPA, commonly in a cylinder with a capacity of up to 5 litres (18 imp gal; US gal) or more. The cylinder can be mounted in a vertical position, on its side, with the air valve facing upwards, or on its rear, depending on the marker type and player preference. Most markers are designed to accommodate a drop forward, an add-on which allows the player to reposition the tank to a more comfortable or more convenient position, and may help to balance the marker and improve its accuracy.

Most markers have a feed system to load and eject paintballs into the barrel, and there are several different types of feeders. These include gravity, agitating and force-feed, the latter two often being referred to as hoppers. Some markers have integrated hoppers, such as the Sheridan K2 and the Worr Games Products Sniper, which communicate wirelessly with the marker’s electronic system to begin feeding paintballs before the marker is activated, removing the need for the player to manually reload.

Some markers, particularly those used for scenario play, are equipped with a harness capable of carrying a tank in addition to pods, to reduce the need for frequent stops to reload and allow for continuous fire. In many scenarios, the marker will need to be fired repeatedly, and a continuous supply of paint is essential for success.