swap bottles are filled and weighed with digital scales, guaranteeing correct amount of gas is provided every time.
due to it being a packaged retail good, the content weight must be correct every time, or the company risks action from regulators.
you have more chance of being 'ripped off' having the gas filled yourself than by buying a swap gas product. here's why -
when having it filled yourself, the filler used to know it is completely full when the gas vents through the bleed screw - this is achieved when the gas is filled up to the 'dip tube' that hangs from the bottom of the valve. problem is, there are varied lengths of dip tubes, and cylinder sizes vary slightly (ie some overseas cylinders have a lower volume capacity) - which can result in more or less gas content with each slightly different cylinder.
so if you have a longer 'dip tube', you get less gas by having it filled yourself. if you have a shorter dip tube, or no dip tube (as happens) - you risk carrying an overfull cylinder which is a safety hazard. it is now a regulation that cylinders must have 20% empty space to allow for expansion in hot weather conditions, and so reducing the occurrence that they will automatically vent.
this came about mostly due to mums and dads buying overfilled cylinders, throwing them in the car on a hot day (with the kids etc), and leaving them there while they shop elsewhere.
to ensure no one overfills and is potentially liable for any action arising from an accident, I would suspect that fillers MAY not fill to the point of the gas venting from the bleed screw, or rather fill by 'feel' of weight etc.
another point raised here related to the out of date stamp - sure there are times when an out of date cylinder may slip through into the swap cage. however we used to inspect, re-valve and pressure test every out of date cylinder that came through from the public prior to filling. and then the cylinder is re-stamped with a new date (and painted if required).
the old date will usually still remain on the cylinder - the operator will usually re-stamp the new date near to the old, but sometimes this isn't possible. just because you see an old date, doesn't mean that the new date isn't elsewhere and that the cylinder is perfectly safe and has been re-generated. my advice is to inspect the cowling around the valve closely for the date stamp - when painted, they can be hard to read at times.
I may be totally wrong, and I wasn't there, but I find it hard to believe that multiple kwikgas cylinders in a bunnings cage were out of date and presented for sale. if you are adamant there were no other date stamps on the cylinders, and each had the blue valve insert (ie they were filled and ready for sale), you should call Kleenheat and report it, or call the Gas Examiner's office in your State or Territory.
