Originally Posted by takagari
Going to have to disagree. Even your explanation tells me that there's just more has directed at the cocking effect. It seems the same amount leaves the striker.
.. gas is being used through out the cycle so long as the valve in the mag is open. with a BB traveling down the barrel, gas is being used to push it out. if you don't have a BB the slide cycles right away and gas that would have been used to push the BB out is instead directed to cycle the slide. since that step of pushing the BB out is skipped, the slide cycles sooner and cuts off the gas sooner thus reducing the amount of time the valve on the mag is open. so less gas IS used when dry firing.
in the simplest terms that i can think of.. the amount of gas used in a gas gun is completely dependent on how long the main gas valve is kept open. that is determined in the case of a pistol by the slide, as it is what re-cocks the hammer and resets the valve striker.
every action the gun goes through during the firing cycle takes a set amount of time. during which the main valve is open and expelling gas. removing one of the actions (propelling a BB) reduces the cycle time and thus reduces the time period at which the gas valve is open.