jwolthuis - 9:16 pm on Jun 7, 2011 (gmt 0)
You received the C&D (i'm guessing) either because you didn't follow their rules, or your compressed gas is flammable and/or toxic.
What is the gas?
You may be able to ship it via Priority Mail or First-Class Package if its non-flammable and non-toxic. You'll need some "ORM-D AIR" labels from Uline, and you'll print a "Shippers Declaration for Dangerous Goods" on a color printer. Takes about 60 seconds to complete, and you'll print 3 copies and sign them.
It's all outlined in USPS Publication 52. I know that publication well, as my post office gave me the same answer, "you can't do that", with some liquids I was shipping. But USPS operates under the rules of the Domestic Mail Manual (which references Publication 52), and local post offices cannot make up their own rules.