The Mk23 would probably run in Antarctica on Duster gas tbf.
I've used my MWS on Green in about 2 degrees C, but only on semi and not spamming the trigger.
I think Nuprol 4.0 is the gas to use while it is this parky. Not used it myself but there are so many factors coming into play with GBBR use in winter, including, but not limited to: gas type used, gas amount in mag, weather, temperature of magazines, lubrication of gun, gaps between shots...