Hi Adammch

The thing with co2 guns is that their performance will vary a lot according to the air temp. I once had a Umarex 850 air magnum that was right up to the legal limit on a hot day but when out and about in the winter it was chrono'd at less than 7.5 ft lbs (3degC outside). Personally I would be very careful about going hunting with a gas gun in the winter. You will certainly have to re-zero your rifle everytime you use it to allow for the change in ambient temp.

Regards

Gunshopboy