So... here is a thought.When you stop by your local fire department, ask if they have any "old bottles".Many of my local FD's are upgrading and have the older 30 minute tanks to "dispose" of. I work with a Volunteer Fire Chief, and another Fireman from a different county. Both keep promising me they will bring me a couple "old" bottles that are still technically serviceable by date... But they never seem to remember.