Recently we were asked whether or not a .223 REM round could be used in a 5.56 chambered rifle. The short answer, yes. But why?
The 5.56 NATO was a round developed in the late 1950’s for the AR-15 and adopted by the military in the early 1960’s. This round was designed to stay supersonic at 500 yards. The .223 round, the civilian version of the 5.56, was purchased by Remington soon after the military adopted the 5.56 for use in the M16.
The .223 REM and the 5.56 NATO are similarly sized cartridges, almost completely identical to the untrained eye, but it is their specific dimensions that define the difference.
The main difference between the two rounds is the pressure. A 5.56 round is designed to create higher pressures than a .223 round. Effectively, a 5.56 round can create pressures up to 60,000 psi where a .223 round may average around 55,000 psi. A 5.56 cartridge wall is slightly thicker to withstand these pressures.
Outside of the cartridge and into the firearm, a 5.56 chambered rifle has a leade (throat) that is almost twice as long as the .223 leade. This results in different pressures within the chamber.
In conclusion, it is safe for a .223 round to be used in a 5.56 chambered rifle, but it is considered unsafe for a 5.56 round to be used in a .223 chambered rifle.
Check out our .223 REM options under the Ammunition tab above.
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