5.56mm is a NATO standard rifle caliber. It’s a very common caliber and has been around since the late 70s. It’s a small and fast bullet with a flat trajectory and little kick. It’s also a relatively small and lightweight cartridge, meaning its easy to carry large quantities of ammunition. Standard magazines hold 30 rounds.
5.56mm is very close to the .223 Remington rifle cartridge, which was developed in 1957 and was the predecessor to the 5.56 round. 5.56 and .223 dimensions are almost identical. 5.56 ammunition has more power and higher chamber pressures than .223. A rifle built for 5.56 can run 5.56 and .223 ammunition. A rifle built for .223 should only ever fire .223 and will not be safe with 5.56mm ammunition. All our rifles in this general caliber are built for 5.56mm NATO, and can run either type of ammunition safely.