Originally Posted by voorhees -FWA-
? dry firing uses less gas?? How?
When the firing pin strikes the striker valve it doesn't know if there's a BB in there or not and will expel as much gas as it's designed too... until the mag has no more gas to expel...
sorry, but most GBBs have a valve system in them that directs gas either forward into the barrel or back to cycle the weapon. when a BB is fired, the valve stays in the back position letting gas into the barrel. as long as that BB is there the gas pressure keeps the valve back. once the BBs leaves the barrel, the pressure drop along with the valve spring(in the case of the positive pressure setup) will then push the valve forward blocking off the barrel and directing the gas now into the expansion chamber so the weapon can cycle. it's the cycling that resets the valve striker (firing pin), it never releases a per-determined amount of gas.
the two types of valve systems are as follows.
positive pressure system: the valve is normally in the forward (barrel closed/sealed via spring behind valve) position unless a BB is chambered and pushes the valve back (open) position via a protrusion extending forward of the valve. (there are many design variations of this but the function is the same.)
negative pressure system: the valve is normally in the back (open, via spring) position regardless if a BB is chambered or not. the valve will only close once the BB leaves the barrel. once the BB is out the pressure inside the barrel and thus on one side of the valve drops. this creates a pressure difference between one side of the valve and the other. when the difference is large enough to overcome the pressure of the spring keeping the valve back, the valve is sucked forward and closes off the barrel, at which point the system will cycle.
so as i said, remove the steps involved in pushing a BB out of the barrel and the gun uses less gas. worth noting, the negative pressure system will use more gas than the positive during dry fire, as the valve starts in the open position.