Paintball guns, called markers, are very precise--and expensive--pieces of equipment. Keeping them clean and calibrated will help you get the most hours of use from them. Plus, a calibrated marker keeps the paintball field fair for everyone, and keeps the play safe.Lower-end paintball guns use carbon dioxide, or CO2, instead of compressed air. Carbon dioxide is a liquid gas that can leak from its tank into the inside of your marker, causing it to freeze up. Short of that, it may just gunk up the internal workings of your gun, slowly wearing down the components. Keep these valves, and the ones for the paintball hopper, clean and properly sealed.
The International Paintball Players Association has established rules for fair and safe play, including shot speed. According to the IPPA, your marker should be shooting balls around 300 feet per second (fps). Use a radar chronograph and the air regulator on your marker to make sure you are firing at a safe speed. (If you or your fellow players don't have a chronograph, most paintball stores or fields will let you use theirs.)
Temperature and elevation can affect the speed of your shot, so recalibrate later in the day if you first calibrated in the early morning. As the day heats up, air expands and paintballs zip by faster. Also, if you plan to play in the mountains, be prepared to check your speed again: at higher elevations, there is less air pressure, and shot speed increases. Play safe, play fair. Play ball.