Picked up a small steel tank at a tag sale for a couple of bucks. It has some gas in it. It’s mostly grey with some green paint on it so I thought it may be o2. Do you think A welding supply store would trade me a co2 tank?
Give it a try what have you got to lose
There are several different valve threads that will tell the professional what was in the tank even if the paper label is long gone, but most dealers around here simply swap tank for tank. They are FAR more interested in selling the gas than quibbling about tanks.
I have welding tanks I take in about every 12 years for refills. The gas dealer never even raises an eyebrow.