Well apparently the Guthrie post office has different rules than the OKC post office. I just stopped by and they said you had to be a dealer or Pawn shop which means you need your FFL.
Ask to speak with the postmaster at Guthrie. They are WRONG!!! They will accept rifles and shotguns from non dealers. Take it to the South OKC station off I-35 near SE 44th and ask for Tina. Tell her I sent ya with your rifle for shipment.
I raised holy hell over there for them to ship my rifle. Contact pstmstr like was stated already. He'll work hard to get the morons lined out. I think he hates stupidity at the PO more than we do.
Here are the rules. They are on the USPS site somewhere, but I can't find them. http://www.cgwgun.com/shipping/usps.aspx
11.3 Rifles and Shotguns
Although unloaded rifles and shotguns not precluded by 11.1.1e and 11.1.2 are mailable, mailers must comply with the Gun Control Act of 1968, Public Law 90-618, 18 USC 921, et seq., and the rules and regulations promulgated thereunder, 27 CFR 178, as well as state and local laws. The mailer may be required by the USPS to establish, by opening the parcel or by written certification, that the gun is unloaded and not precluded by 11.1.1e.
Knowing now that it is legal to ship a rifle, I'll probably never tell them it is a rifle or shotgun again. Just box and ship.