I don't think MSR ever refilled the canisters (even pre-covid). They just recycled them when you brought them in. If I was MSR I wouldn't refill a canister some random person brings in. If the canister they attempt to fill has been tampered with it could seriously injure an employee (or worse)

@noah that's not too bad either as I'd trust MSR to at least try and salvage the metal properly instead of just burying it in a landfill...

It's also worth noting in the USA it is apparently illegal to transport refilled fuel containers. So if you plan to drive with them you may be breaking the law.

Round here they're recyclable with food and drinks cans, or with mixed metals at the municipal recycling facility. That's probably your best bet. Unlike some answers I reckon the risk is at the time of refilling, and they'd be essentially as safe as new in the field. I still wouldn't do it, not knowing the pressure the canisters are designed for. That's despite having a 4.5kg cylinder of butane in my campervan and most of the plumbing I'd need to connect them together

While the idea isn't a good one, the question is perfectly reasonable - votes are meant to be about question quality, not the underlying idea.

I'm not sure if the same distinction is used in the US, but in the UK, the small disposable containers of gas are called "canisters" and the big refillable ones "cylinders". The latter are normally exchanged for a full one and are of heavier construction like gas cylinders you'd see in other uses . Thus in the terminology I'm used to you'd be trying to refill a canister from a cylinder.

@chrisH I see similar usage in the US, though "tank" is more popular than "cylinder," especially for propane.

@barbecue here a tank would be bigger still, permanently located outside a house without mains gas and refilled by a delivery lorry (or truck, while we're on different terminology)

@ChrisH around here it seems to be more a matter of the shape than the size. Cylinder usually refers to taller, thinner tanks such as those used in welding or for CO2. Tanks are usually more squat, though there are no real rules.

there are other fuels that you can use that don't come in a pre-made metal can, too.

@noah yes it’s illegal but it is a blatant case of the Federal government abusing the Commerce Clause and the 10th Amendment.

There is a fairly broad class of "DIY safety questions" where the only correct answer is "if you personally don't know the safety issues associated with the procedure and you don't know how to evaluate the risks, then it is not safe for you to attempt to do it. This question is one of them, IMO.

@alephzero The fact that OP decided to accept the answer that tells you how to do the thing really pushes my buttons. I don't consider this to be something that should be on TGO.

@Gabriel that info has now been removed from the answer.

I’m voting to close this question because it promotes or seems to promote a safety risk.

Question closed on request of a user.

The close vote makes no sense at all to me. The question is clearly on topic, and a safety risk is far better dealt with by answering than pretending the problem doesn't exist

@ChrisH - the question is asking "how to" - which is a safety issue. The real answer is "DON'T!" so it's not a valuable question that is in scope. On various SE sites we close or delete posts that could be seen to be encouraging dangerous or illegal behaviour. This is one of them - there is no way to consider refilling these canisters to be safe. And in many places no legal way to do it either.

@RoryAlsop Why "Don't!" though? You're saying this as it has to be obvious, without explaining the nitty gritty of what exactly could go wrong.

that's what my question is basically asking

if its "obvious", surely it would be easy to write down in an answer? If its not obvious, then its even more puzzling

that's the annoying part about i.e. MSRs warnings. Instead of making a video on refilling where they try it out in a lab and those cans (say) explode most of the time, they just say "DON'T!" and leave it at that

and of course shutdown their recycling program under the excuse of COVID, but I digress

in any case I've since found 1-pound canisters that are "officially" refillable, though people complain about leaky valves in reviews so I'm not sure how much safer it actually is...