Sorry to bust your bubble, but 5 or 6 batches does not qualify as magical. Granted you're using gas for cleaning as well, but I normally get 10-12 kegs out of a 5 lb tank using it for only carbing and dispensing.
__________________ Slots Down Brewery
Stick with the plan....not the sparge.
Yeah I saw a chart somewhere that says how many corneys you can push with each tank size. It's pretty crazy.
With the amount of beer I make I inevitably lose a tank to a faulty poppet or some other silly thing. I'm pretty careful with checking kegs and lines over but it still happens occasionally. I have three 20 pounders and a ten pounder so there's always at least a backup. I purge carboys and kegs with CO2 before racking into them so the spares are nice to have around.
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I usually get about 4 kegs from a 20oz(1.25lb) paintball tank
My son doesn't brew, but is building a kegerator to have commercial beer on tap and the occasional keg I bring down when I visit. For Christmas I ordered him the KegConnection kit that uses the 20oz tanks. For only pushing beer that's already carbonated it'll last a long time and they're easy to fill at sporting goods stores.