From UPS website:
"How to Ship Ammunition (Cartridges, Small Arms)
UPS accepts for transportation such ammunition as constitutes "cartridges, small arms," as defined in 49 C.F.R. § 173.59. All other allowable ammunition shipments are accepted only on a contractual basis, and must be prepared under the rules for a fully regulated hazardous material.
Ammunition will be transported only when packaged and labeled in compliance with 49 C.F.R. § 172 (Hazardous Materials), and must be shipped in accordance with the UPS Guide for Shipping Ground and Air Hazardous Materials. To meet the exception for Limited Quantity/ORM-D, ammunition can be shipped via UPS Ground only within the 48 contiguous United States, UPS Ground Intra-Oahu and Intra-Alaska.
To qualify as "Cartridges, small arms ORM-D" or limited quantity, ammunition must be:
Ammunition that does not exceed 12.7 mm (50 caliber or 0.5 inch) for rifle or pistol cartridges or 8 gauge for shotgun shells; or
Ammunition with inert projectiles or blank ammunition"