I run a WE 416, and a lot of times I will use co2 mags as opposed to green gas because of weather conditions. The mags use 12g co2 cartridges, but even with these cartridges I am barely able, or sometimes, not at all able to get a full 30 rounds out of the mag. And I shoot semi auto only. Anyone have any answers, or have you experienced the same issue. When I use those same mags in my WE pdw, I can get a mag and a half or almost 2 before I have to change the cartridge.
From what I remember about gas blowback rifles, Puma is pretty much correct. I'm no expert in gas physics, but basically CO2 stays at a pressure high enough to operate a GBBR longer than propane at low temps. However eventually yes, it will cool down too much. One of the major factors is how much gas is being used per weapon cycle. In a GBBR, you're moving a bolt back and forth, so some gas is escaping as it cycles and not really doing much if any work. Even in gas pistols you see differences in operation. Some designs work much better in cold than others. A good example of this from my own personal experience is a stock TM 1911 on propane/green gas. When I had one it functioned much better in the cold than other brands and models of pistols. This may have been due to the single stack design of the magazines or something else, I'm not sure. Non-blowback gas guns work even better, because there are so few parts that have to move that not much gas needs to be released.
Basically, gas operated guns just aren't well suited to operation in the cold.