Here it the skinny right from the source:
From UPS
https://www.ups.com/us/en/help-center/packaging-and-supplies/special-care-shipments/firearmsHow to Ship Firearms or Ammunition
Special Procedures for Shipping Firearms
UPS accepts packages containing firearms (as defined by Title 18, Chapter 44, and Title 26, Chapter 53 of the United States Code) for transportation only (a) between licensed importers, licensed manufacturers, licensed dealers, and licensed collectors (as defined in Title 18, Chapter 44 of the United States Code), and government agencies and (b) where not otherwise prohibited by federal, state or local law (i) from an individual to a licensed importer, licensed manufacturer, licensed dealer, or licensed collector; and (ii) from a licensed importer, licensed manufacturer, licensed dealer, or licensed collector to an individual.
The shipper must comply with and must ensure that each shipment containing firearms complies with all federal, state and local laws applicable to the shipper, recipient, and package, including, without limitation, age restrictions.
UPS accepts firearm parts for shipment, provided the part is not a "firearm" as defined under federal law; the contents of the package cannot be assembled to form a firearm; and the package otherwise complies with federal, state, and local law. (Note: Receivers or frames of a firearm and firearm mufflers/silencers (also referred to as suppressors) are considered "firearms" and are accepted for transportation only if shipped in accordance with UPS's requirements for shipping firearms.)
Getting Your Firearm Shipment to UPS
Firearms (including handguns) may be shipped only through a UPS Scheduled Pickup Account (specifically, Daily Pickup, Daily On-Route Pickup, UPS Smart Pickup®, and Day-Specific Pickup), or through a UPS Customer Center (counters at UPS operational facilities). Note: Firearms (including handguns) are not accepted for shipment via UPS Drop Boxes or UPS On-Call Pickup®, and may not be tendered to or dropped off at locations of The UPS Store®, any third party retailer, or any UPS Access Point™ location.