I get cold fingers and toes very easily. I believe it is a by product of growing up in Minnesota and being frostbit on numerous occasions. In any event, hand and foot warmth is important to me and this is what I use for bird hunting.
These are the best shooting gloves I've ever usedOutdoor Research Gloves
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They are wind and waterproof. Do not buy them to be tight, but they will stretch very nicely to fit your fingers without bunching up and without floppy finger tips.
If these are not enough, then slide your gloved, left hand into one of these Burton Workhorse Leather Chopper Mitten
while keeping your gloved right hand in your jacket pocket for the first 30 minutes of hunting. After that, you should be fine with just the gloves and no mitt.
If that doesn't do it, then a pair of these. Zippo hand warmers
Slide one inside each wrist cuff of a long glove, or more likely, inside the wrist elastic of your hunting parka. Keep them against your wrist where the blood is shallow and easily warmed as it passes by. This will work, even when sitting on a deer stand.
If none of that works - maybe it's a good day to stay home.
I should add, proven effective with double triggers on Scott, Lang, Evans, Greener, Cashmore, Merkel, and numberous flint and percussion muzzleloaders.