Now most players use semi or even full auto paintball guns and the limitations of CO2 are exacerbated. The problem stems from the temperature and pressure drop in the tank as gaseous CO2 is withdrawn. The faster you shoot, the faster CO2 is changed from a liquid to a gas in the tank, and the faster the temperature and pressure drops in the tank. Full Autos and tricked out semis with high rates of fire are affected the most by this problem. I have frozen 20 oz tanks from top to bottom with continuous full auto fire.
High heat can also cause problems.
Regulators will limit the maximum pressure that will reach your gun. Regulated HPA gives consistent pressure until the tank pressure drops below the regulated pressure, unlike CO2 that drops pressure incrementally as gas is withdrawn from the tank. Even regulated low pressure guns on CO2 use such a high volume of gas that the tank pressure can drop below the regulated pressure before the tank is empty. HPA is a much better power source, but the setups are expensive and HPA is not as easily available as CO2. Watch your rate of fire and don't shoot when don't really need to.