Changed in August 2020 - you didn't read far enough, you may not use USPS for muzzleloading handguns:
432.2 Handguns
Handguns and other firearms capable of being concealed on the person are nonmailable unless mailed between the parties listed in this section, after the filing of an affidavit or statement described in 432.22 or 432.24, and are subject to the following: a. Firearms meeting the definition of a handgun under 431.2 and the definition of curios or relics under 27 CFR 478.11 may be mailed between curio and relic collectors only when those firearms also meet the definition of an antique firearm under 431.3. b. Firearms meeting the definition of a handgun under 431.2, which are certified by the curator of a municipal, state, or federal museum that exhibits firearms to be curios or relics of museum interest, may be accepted for mailing between governmental museums without regard to the restrictions provided for handguns in 432.21 through 432.24 and Exhibit 432.25. c. Air guns (see 431.6) that do not fall within the definition of firearms under 431.1 and are capable of being concealed on a person are mailable, but must include Adult Signature service under DMM 503.8. Mailers must comply with all applicable state and local regulations. d. Parts of handguns are mailable, except for handgun frames, receivers or other parts or components regulated under Chapter 44, Title 18, U.S.C. e. Mailers are also subject to applicable restrictions by governments of a state, territory, or district
Below are some guidelines for shipping firearms and ammunition, along with notes related to specific shippers. We encourage you to review the specific shipper's web site as shippers have different guidelines.
You must ship to an FFL holder:
Federal law requires all modern firearms be shipped to a holder of a valid Federal Firearms License (FFL). Any person who is legally allowed to own a firearm is legally allowed to ship it to an FFL holder for any legal purpose (including sale or resale).
Here is what the ATF "Federal Firearms Regulations Reference Guide"' (ATF P 5300.4) says:
(B9) May a nonlicensee ship a firearm by carrier?
A nonlicensee may ship a firearm by 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 178.31, 27 CFR 478.31 and 478.30]
(B8) May a nonlicensee ship a firearm through the U. S. Postal Service?
A nonlicensee may mail a shotgun or rifle to a resident of his or her own state or to a licensee in any state. Handguns are not mailable. A common or contract carrier must be used to ship a handgun. A nonlicensee may not transfer any firearm to a nonlicensed resident of another state. The Postal Service recommends that longguns be sent by registered mail and that no marking of any kind which would indicate the nature of the contents be placed on the outside of any parcel containing firearms.
[18 U.S.C. 1715, 922(a)(3), 922(a)(5) and 922 (a)(2)(A)]
The section of the US Code governing modern firearms is called Commerce in Firearms and Ammunition (CFA). This code is available online: http://www.access.gpo.gov/nara/cfr/waisidx_09/27cfr478_09.html
When in doubt, we suggest arranging for transfer through a licensed dealer. Violation of the CFA is a felony, and penalties for violation are severe.
If you do not have a Federal Firearms License:
Any shipper who does not have an FFL is considered to be an unlicensed person. Unlicensed persons must ship modern firearms to a licensed FFL dealer only. If the buyer is not licensed, they will need to make arrangements to have the item shipped to a licensed FFL dealer in their state.
Before you ship a gun, the buyer must fax or mail you a copy of the dealer's signed FFL license. You can only ship the gun to the address on the license. You should take the copy of the signed FFL with you when you take the item to be shipped in case the shipper wants to see it.
Antique firearms:
Antique firearms need not be shipped to a licensed dealer. They can be shipped directly to the buyer. Click here for a definition of Antique firearms.
Knives, air guns, accessories, and most gun parts:
These items need not be shipped to an FFL holder. Note, however, that each firearm contains at least one part the ATF considers a firearm, typically the part containing the serial number. This part must be treated as a complete firearm when shipping the item.
AFTER THIS I DON'T CARE ANYMORE....