Luckily I have a talented fellow on my forum by the name of Buck Conner that does a lot of writing, research, etc.
I remember oldbob47 making a comment on how worthless double set triggers were because you can't use a glove and that your hand would get cold. As a hunter, its pretty obvious what I personally would and do in fact, use. But to some, it escapes their minds..
Buck put this info up on my face. Real accounts from those mountain men of the past.
PERIOD MITTENS
If your involved in living history, you should have historical references for what your using. If questioned you have the information to stop the "in-the-know" person in their tracks. I have had a three ring binder (using protector sheets) with pages of historical references for my equipage, carried for over 30 years. If questioned (AMM & NAF) will do this once in a while. Then you give them a history lesson and watch them walk away with their tail between their legs. 
Here's a reference on mittens, lined with rabbit fur & otherwise:
"of all furrs the furr of the hare is the warmest, we place pieces of it in our mittens, the skin is too thin for any other purpose." c. 1800, Hudson's Bay (David Thompson, Narrative, 31)
"... in the intense cold, the shot is no sooner fired than our hands are in our large mittens; we walk and pick up the bird, then get the powder in, and walk again, at length [put in] the shot, and the gun is loaded; it is needless to say, exposed to such bitter cold, with no shelter, we cannot fire many shots in a single day. Gloves are found to be worse than useless." c. 1800, Hudson's Bay (David Thompson, Narrative, 31)
(Remember the "mittened hand" that the large trigger guard on the NW trade gun is supposed to be for? Well, Thompson is clearly taking his mittens off to shoot.)
"I fortunately escaped [frostbite], by the aid and assistance of a pair of rabbit skin gloves with which I kept constantly chafing the places affected..." Dec 9, 1820, Fort Providence on N. shore of Great Slave Lake (George Back, Arctic Artist, 103)
"We employed ourselves in making mittens of old deer [caribou] skin that was found lying about--I made a pair also..." October 10, 1821, Obstruction Rapids of Coppermine R (about halfway between Great Slave Lake and Coronation Gulf on the Arctic Ocean). (Back, 184)
Like the old Boy Scout moto "be prepared", if you are as much as possible, you keep surprises to a minimum.