This might help:
Shipping Firearms
It is perfectly legal to ship a firearm in-state between individuals, without involving a licensed dealer.
I'll refer you to the ATF to prove this, because you won't believe me:
http://www.atf.gov/firearms/faq/unlicensed-persons.html#shipping-firearms-carrierQuote:
Q: May a nonlicensee ship a firearm by common or contract carrier?
A nonlicensee may ship a firearm by a common or contract carrier to a resident of his or her own State or to a licensee in any State. A common or contract carrier must be used to ship a handgun. In addition, Federal law requires that the carrier be notified that the shipment contains a firearm and prohibits common or contract carriers from requiring or causing any label to be placed on any package indicating that it contains a firearm.
[18 U.S.C. 922(a)(2)(A), 922(a) (3), 922(a)(5) and 922(e), 27 CFR 478.31 and 478.30]
Okay, now we have that covered.
So, how do we go about shipping a firearm in-state?
First of all, the box you put the firearm should not be marked in anyway to indicate that it is indeed a firearm.
Rifles
Rifles are easy. Put them in a box. Take them to the counter at the post office. Inform the clerk that you are shipping a rifle. You're required by federal law to inform the shipper that the package contains firearms. There's no additional fee to ship a rifle. Standard postage applies. If you're smart, you'll pay for delivery confirmation and insurance.
Pistols
Pistols are a pain in the [potty-mouth]. USPS won't accept them. You can ship them via FedEx or UPS. Both carriers require that you ship from a hub, and that you use overnight service to do so.