woah woah woah hold up there, a stock TM MWS with green gas will struggle at 0°C and it's unavoidable. This kind of freezing weather is simply out of the effective operating temperature range of green gas. The chart below says that Green gas/Nuprol 2.0 at 10°C will have a pressure of 5.6 bar/81 PSI which is really weak already, even Nuprol 1.0 says that it operates at 8 bar/115PSI, at it's optimal temperature. I get around 1 magazine of "full power" shots out my a single mag fully gassed up with green gas at a temperature of 9°C. My first shot clocks in at 89m/s (281fps) and my last few end up around 79m/s (256fps) and there is a very significant difference in feel and sound between those first and last shots too. The first 10-15 shots are very consistent, but then the magazine starts to get cold as shit and the fps dips by 1m/s every other shot. Also bear in mind my magazines are the newer versions which supposedly don't require the green gas mod.
The saving grace here is that you can simply run higher pressure gas such as red (nuprol 3.0) at these kinds of temperatures. Red/Nuprol 3.0 at 10 degrees will have a pressure of 7.7 bar which is perfectly acceptable for an MWS, and if you're at sub 0 temperatures, black gas is likely your only option or HPA tapped magazines, but lets be honest we're using GBBRs so we DONT have to carry around a damn air tank so that's not an option 😁
Also, you can simply get a light weight/aluminium bolt to improve your gas efficiency in cold weather. There are quite a few options out there too.