9x19mm
9mm is the standard pistol and/or sub machine gun round of OSEAN.

5.7x28mm left of 5.56x45mm Ammunition

5.7x28mm
5.7mm is the optional secondary choice for pistols, sub machine guns, but is usually chosen for PDWs. It provides better armor penetration than 9x19mm.

(5.56 shown next to a ruler)

5.56x45mm
5.56mm is the standard intermediate round for all militaries within OSEAN.

(.280 NATO shown in various types and casings.)

.280 OSEAN
.280 OSEAN is the standard full-Rifle round of OSEAN.

(7.5mm OSEAN rounds in line with each other.)

7.5x55mm OSEAN
7.5mm OSEAN is the optional full-power rifle cartridge for OSEAN.

12 Gauge
12 gauge is the standard shotgun shell for OSEAN nations

12.7x99mm (.50 BMG)
12.7mm is a standard HMG and/or Anti-Tank/Materiel Rifle cartridge.