I posted earlier showing some calculations that support Jim Tyler’s findings on the effect of temperature on muzzle energy, and I got to thinking further. WARNING - DON’T CONTINUE READING THIS POST IF YOU LIKE TO SHOOT AND THINK EQUATIONS ARE A WASTE OF TIME! The internal energy of the air in the regulator is the only source of energy used to propel a pellet from a PCP gun. The internal energy can be calculated from: Internal energy for a diatomic gas = 5/2 NkT = 5/2 nRT - Eqn 1 (Air consists mostly of nitrogen and oxygen which are both diatomic gases.) where N = number of molecules; k = Boltzman constant; T = gas temperature in Kelvin; n = number of molecules; R = gas constant The ideal gas law states that: nRT = PV - Eqn 2 where P = pressure; V = volume Inserting equation 2 into equation 1 shows that the energy available can be calculated simply from: Internal Energy = 5/2 P.V Inserting typical values shows that P = Regulator pressure = 90 bar (say) = 9 x 106 Pa = 9 x 106 N m-2 V= Volume of air in the regulator = 1.5 cm3 (approx..) = 1.5 x 10-6 m3 Estimated Internal energy = 13.5 J = 10 ft lb So, the estimated value is a bit low and the calculations ignore frictional losses of the air and the pellet to barrel contact. Nonetheless, not far off.