Read the regs. They are short and consise. No UPS Store, no box drop off. Customer service center or hub drop off, or pickup depending on your account.

https://www.ups.com/us/en/help-cent...rdous-materials/shipping-ammunition.page

excerpt from the site:

Getting the Package to UPS

Cartridges, small arms may be shipped only through a UPS Scheduled Pickup Account using various UPS pickup services , or through a UPS Customer Center (counters at UPS operational facilities). Note: Cartridges, small arms are not accepted for shipment via UPS Drop Boxes, and may not be tendered to or dropped off at locations of The UPS Store® or any third party retailer or UPS Access Point™ location