How low should I go ?

Are you using a flowmeter with a vertical tube and a steel ball inside? That's the best one to use. phil k.

Single stage regulators as commonly used for shielding gas have the output pressure rise as the input pressure drops so it might be that you have excessive flow causing turbulence and drawing in air due to the low input pressure, do you have a flow meter on it. No reason you shouldn't get correct shielding with 250psi in providing the regulator is adjusted to suit.

Yes , but it was acting erratically today . That's part of why i think it's time for a fresh bottle . This one only lasted me 5 years ... I don't weld much .

I do have a flow meter on it , and it was acting a bit weird today ... but not excessive flow . I can't complain, I think I last filled that bottle like 5 years ago .

Ok. The next simple test would be to hold a small plastic bag over the torch and tap the petal. If you have gas flow the bag fills up. If not, then there may be a torch line problem. Plugged? Pinched? Leaking?

I have to laugh. The rather expensive (for me) Miller 212 dual stinger came with a pair of Smith dual round gage type "flow meters," and the relatively cheap (by comaprison) AHP TIG welder came with the ball type flow meter.

I have seen that affect with OA when cutting right down to the end of the bottle.

I see it regularly as I vent the pressure in the regulator after closing the bottle valve on my MIG and TIG gas bottles, the content needle drops and the outlet pressure rises until there is no pressure left then the outlet pressure drops to zero.

I use high quality ball type flow meters on my argon and C25 cylinders. I can run a cylinder down to 30 psi before the gas flow gets wonky. I usually don't let the cylinder pressure drop lower than

After discovering that the steel I was welding was the problem , I decided to wait until mine gets that low .

Yeah, no sense in wasting gas you paid for. Eric