I usually cut it off at -20. Below that it's too hard to get the snow machines started. A .58 cal muzzleloader loaded with 80gr of powder will only shoot about 45 yards at -30. My 30-06 looses a lot of velocity colder than -30 also. Tried to take a shot at -50 one night at a wolf, when I pulled the hammer back on my winchester 94, the spring broke. Any oil, grease, or residue will stop the firing pin from moving in sever cold on bole guns. I saw my hunting partner have a cable brake at -25 on his compound bow. I won't pull a bow myself after -10. At -10 I've had the plastic knocks come apart, and graphite arrows shatter on the rest at -15 when released.
Want to ruin an old VW engine? Try running it after -45, if you can get it started. The oil will not heat up enough to flow, the air cooled engine will not develop enough heat to thin out the oil. I use the same cover over the front of my Diesel pickup as the Semis use down south. If it's colder than -30 I let it run for a minium of 30 minutes before trying to move it to let the transmission warm up. The transmission cooler becomes a heater when it is that cold. The transimission fluid is routed through the radiator to help warm it up from the engine heat. I don't shut it off from the time I leave home till I return, when it's -30 or colder. At minus 65, I've seen people park their trucks outside a quick stop, go in for 30 minutes, come out and their tires be frozen down. Instead of warming them up, or chipping loose the ice they are parked on they jump in the truck and crank down on the throttle. They rip a chunk out of their tires, instant flat. A few weeks ago my teenage son was out and hit a pothole. It was -55 that night, and he popped the beads of two tires off the wheels. The sidewalls were frozen, and when he hit the pothole off they came. But the tires were so hard, they held the truck up for a while. He said the truck got squirrelly, but kept going. Then suddenly he was running on the rims, the tires came off the wheels and wrapped aroung the axles. One night I was going back to the shop with the shop van, a 1 ton metro van. I had to cross the railroad tracks at the usual crossing. I was going about 15 mph, usual speed was 35 mph, broke both front springs when I hit the crossing, it was -65 that night. Metal becomes brittle at those tempatures. Open your tailgate after -40 and you will not get it closed without ripping those little rubber bumpers off, or taking it inside to warm up. You go outside to start your car or truck at -65, it's plugged in so it starts. When you go to go back inside the door won't close,don't slam your car door after -65, the windows will shatter, and you WILL not drive it with a window missing. And duct tape don't stick at that temp also so you can't cover the open hole. Push the door to, then lean something against the door to hold it as close to closed as possiable. Let the car warm up, (usually 20 to 30 min) the heater will thaw out the door seals enough the door will then close. When it's colder than -65, you get out of your car then you know you have to close the door. You also know that as soon as you touch that door, static is going to knock the heck out of you. At this point women will usually start crying, they will kick the door with their boots, anything to keep from touching that door with their hands. They will even try to get strangers to close the door for them. I've seen women come inside after grabbing that door and getting the heck knocked out of them so bad they peed all over themselves (and a few men as well). There is a trick here, put your keyring on your finger, then while holding the key, touch the door with the metal key. The spark will jump to the key and you will hardly feel it. Be very cautious fueling up at cold temps. That static and gasoline don't mix well. Everyyear we have a few vehicles burn at the pumps, while trying to refuel. At -65 or colder, when you start off with a vehicle, all the wheels have a flat spot, don't go fast till that flat spot rounds out, if you do you run the chance of knocking the bead off the wheel because the sidewalls are too stiff to absorb the shock. The sidewalls have not give so the bead pops off when the flat spot hits. After -50 I totally cover the radiator on my vehicles, they won't overheat. I open the hood and slip a piece of cardboard in front of the radiator. On most trucks after -55 the heater blower will overwhelm the heater, so you need to turn the blower down to medium, otherwise no heat inside. Last year I had a 97 F-150. Usually it needed oil every fourth tank of gas. It was time to check the oil, and it was -55 that night. I raised the hood, checked and added oil. When I went to close the hood it would not latch. I lifted the hood about two inches and dropped it. It latched, also the plastic pieces around the headlites and grill shattered. We use block heaters (take out one or two freeze plugs and install one of those in the opening), As for Diesel we only use #1 during the winter, #2 will gel and not flow. There is also an addative we use when it is going to be colder than -65 to help the fuel flow. Don't take a vehicle inside unless you are going to leave it long enough to dry out. If you take one inside the cold parts will condensate and get covered with a layer of moisture. If you take it right back outside, you step on the brakes, they freeze in place and will not release. When you hit the gas sometimes they pop loose, sometimes they don't. I often see little front wheel drive cars running around with one rear wheel not turning. The people took it inside and one rear wheel brake did not let go after they pulled out of the garage. They usually don't realise it till they make a corner, then they go into a spin. Don't use your parking brake ever in the winter, moisture in the brake cable line will prevent it from letting go also.
At -70 most matches won't strike, and if you get it struck, it won't light a sliver of wood. Most lighters don't work then either. In fact it's hard to get a candle to light at -70. But that is the best way to start a fire at a cabin. Light a candle, then work on the stove. You can light small sticks off the candle, saving your matches. To start a stove, I usually use oil, then put a small puddle of gas in the middle of it. That will light, but you better know what you are doing (again don't allow fumes to build up). To start a fire outside, pour a small can half full of gas, set it down then immediately light it(don't give the fumes time to build up). Place wood over the can, being careful not to spill the can. In a few minutes you will have a fire. Propane lanturns and stoves don't work below -45, without some engineering. They scare me, I saw my father-in-law blow up a house trying to get a propane stove to work at -65. I don't use propane period.
At -75 and -80, I've seen Birch trees explode. The small amount of moisture inside was too much, it froze and the pressure kept building till it litterally exploded the trunk of the tree. I went to bust a lock open one night using a hammer, the head of the hammer shattered, it was -65. A couple of weeks ago a friend bumped my snowmachine hitting the Kolpin case, the case shattered like glass, it was -35 that night. I've had the cutting edge of an ax chip trying to cut kindling at -65. I've seen saw blades shatter at -65 when someone tried to cut with them.
And your best friend when you have to go to the outhouse at -65 is a good union suite. The heck with two piece thermals, give me a union suite. Most of you can figure that one out.
