>”However I don’t really want to carry around 1 lb propane tanks, even if I’m dragging a pulk.”
Yeah, I learned that on one snow-camping family trip. I figured, “it’s all in the pulk, what does weight matter?” and threw in propane cylinders and nice dry wood but you still have the work of hauling any weight up a hill and the more a sled weighs, the more you’re going to compress the snow and that’s all work that you’re doing. So now I’m only heedless of weight in the sled when the access is all on a frozen lake AND there’s not much snow pack on the lake.
Pro-tip: put a nordic-skiing glide wax all over the bottom of your sled/pulk. It really helps. And minimizes the chance of the base icing up if you move in and out of the sun through thawing and then frozen snow.
Why not refill a standard iso-butane (or butane-propane-mix) canister with 60% butane and 40% propane or even higher by mixing ingredients, mark it as such, and only use it in winter? Or just use 20% of the original contents and top off with straight propane?
I used to caution against that since, as you connect the propane source to the backpacking canister, the canister will see propane’s full vapor pressure (it won’t instantly mix with the butane and have an intermediate vapor pressure – that would come after the liquids mix completely). But after re-reading Roger’s 2007 article ( https://backpackinglight.com/exploding_gas_canisters_the_hazard_of_overheating/ ) in which he intentionally took a canister of 30% propane / 70% isobutane up to 98 °C (208 °F) to make it explode. A seriously DON’T TRY THIS AT HOME, KIDS experiment.
He concludes that standards for the canisters and previous advice to never exceed 50 – 55 °C (122 – 131 °F) still stand, but one can be reassured that there is a considerable safety margin at that temperature with 30/70 or 40/60 mixes.
To get the same margin of safety with pure propane (during refilling from a pure propane source), would require the donor propane never be above about 27°C (80°F) so one should never heat a donor propane cylinder, ever, but rather cool the receiving canister (or not, since the donor propane naturally has a higher pressure). To actually burst a canister, which Roger did at 98°C, would take about 68°C (154°F) if you had pure propane in a backpacking canister* ** ***.
* But that’s with NO safety margin
** And no allowance for a dent or rust spot or manufacturing flaw in the canister
*** Remember that transport and storage can easily heat a canister up (a car left to warm up, left in the sun, a canister stored near a heater vent, etc, etc).
I’m getting tempted to refill a canister with pure propane and then put it in a water bath far, far from the house and blow it up, recording at what temperature that happens.
There’s a long list of caveats if you’re putting pure propane into backpacking canisters. One of which is that liquid butane is 1.16x the density of liquid propane, so if you fill to the same weight, you’ll have more liquid volume inside. That’s bad. So 100 grams of butane should only be replaced with 86 grams of propane to maintain the same headspace / freeboard inside.
.
