I've spoken to the UPS Hazardous Materials Support group about this and successfully shipped ammo via UPS in the past. Here's the scoop.Slngblde said:
UPS will accept the package as long as you are at a true UPS distribution center -- not one of those mail centers where UPS comes by to pick up/drop-off. There are no special fees for loaded ammo. Write ORM-D on the box in big black letters, and draw a big black box around the letters. Above the box you just drew write "“Cartridges, small arms”. (That text doesn't need to be in big fat pen letters). They will only ship it UPS Ground. They will only ship to lower 48. It cannot exceed 66 pounds.
If the desk jockeys don't want to accept it, tell them to call 800-554-9964 and the Hazard Materials Support group will straighten them out. HTH.
-- Steve