It's 1.4S explosive.
Understand that ORM-D isn't a class. The hazard class is 1.4. ORM-D is an exception that allows small arms ammo that meets the below requirements to travel under the ORM-D rule. Small arms ammo is and always has been considered 1.4 explosive (or class C explosive before the UN system, and still class C explosive under OSHA)
Small arms ammo can ship as ORM-D if it meets the following:
(b) Cartridges, small arms, and cartridges power devices. (1) Cartridges, small arms, and cartridges power devices (which are used to project fastening devices) which have been classed as a Division 1.4S explosive may be reclassed, offered for transportation, and transported as ORM-D material when packaged in accordance with paragraph (b)(2) of this section; such transportation is excepted from the requirements of subparts E (Labeling) and F (Placarding) of part 172 of this subchapter. Cartridges, small arms, and cartridges power devices that may be shipped as ORM-D material is limited to:
(i) Ammunition for rifle, pistol or shotgun;
(ii) Ammunition with inert projectiles or blank ammunition;
(iii) Ammunition having no tear gas, incendiary, or detonating explosive projectiles;
(iv) Ammunition not exceeding 12.7 mm (50 caliber or 0.5 inch) for rifle or pistol, cartridges or 8 gauge for shotshells; and
(v) Cartridges, power devices which are used to project fastening devices.
(2) Packaging for cartridges, small arms, and cartridges power devices as ORM-D material must be as follows:
(i) Ammunition must be packed in inside boxes, or in partitions which fit snugly in the outside packaging, or in metal clips;
(ii) Primers must be protected from accidental initiation;
(iii) Inside boxes, partitions or metal clips must be packed in securely-closed strong outside packagings;
(iv) Maximum gross weight is limited to 30 kg (66 pounds) per package; and
(v) Cartridges, power devices which are used to project fastening devices and 22 caliber rim-fire cartridges may be packaged loose in strong outside packagings.