if you've seen the scoutthedoggie vids with Daedalus and his WE M14 EBR
he talks in this one about using Propylene, especially for cold weather
WE M14 Airsoft Gun Details Section8 Scotland - YouTube
Availability is no issue, you can find it at Home Depot, Canadian Tire etc and it uses a "CGA 600" fitting just like the propane tanks.
I do have questions regarding its volatility compared to propane as well as propylene's status as a "Volatile organic compound".
It is supposed to be a little harder on your gun as well.
Anyone actually used it?
http://www.canadiantire.ca/AST/brows....jsp?locale=en