The Mass of the gas is one thing. The volume of gas is a whole different matter.
Of course.
Different topic......
A wrong idea that gets repeated over and over is that it's the initial temperature of the powder that affects muzzle velocity. Actually, it's just as was stated by Idaho Shooter: Cold steel robs more heat energy out of the gas than hot steel does. Ammunition temperature matters a little, but only because the brass and lead rob energy as well. Barrel temperature is about 3X as influential as brass and lead temperature.
