The 5.56 cartridge has a different neck angle from the .223 Remington, generates higher chamber pressures, and has different weight projectiles available. .223 Remington can be safely cycled through a rifle with a 5.56 chamber, but it is not recommended to use 5.56 ammo in a rifle with a .223 chamber.
A rifle with a 5.56x45 chamber can utilise .223 Remington cartridges. A rifle with a dedicated .223 Remington chamber cannot accommodate 5.56x45 cartridges. A rifle with a .223 Wylde chamber can accommodate .223 Wylde, .223 Remington, and 5.56x45, but neither a rifle with a 5.56x45 or a .223 Remington chamber can accommodate the .223 Wylde cartridge.
.223 Remington can be cycled in a 5.56x45 rifle; 5.56x45 should not be cycled in a .223 Remington firearm.
No.
223 Remington.
.223 Calibre although .223 Will fit on a 5.65 mm, a 5.65 mm Will not fit in a .223 calibre chamber.
Shank (.223 Remington) - 0.4370 / (NATO 5.56) - 0.4370 / (Difference) - 0.0000 Base Diameter (.223 Remington) - 0.3760 / (NATO 5.56) - 0.3780 / (Difference) - 0.0020 Shoulder Diameter (.223 Remington) - 0.3553 / (NATO 5.56) - 0.3560 / (Difference) - 0.0007 Neck-2 (.223 Remington) - 0.2550 / (NATO 5.56) - 0.2550 / (Difference) - 0.0000 Neck-2/Case Mouth (.223 Remington) - 0.2540 / (NATO 5.56) - 0.2550 / (Difference) - 0.0010 Freebore Diameter (.223 Remington) - 0.2245 / (NATO 5.56) - 0.2270 / (Difference) - 0.0025 Pilot Diameter (.223 Remington) - 0.2180 / (NATO 5.56) - 0.2180 / (Difference) - 0.0000 Base-to-Case Mouth (.223 Remington) - 1.7720 / (NATO 5.56) - 1.7750 / (Difference) - 0.0030 Base-to-Shoulder (.223 Remington) - 1.2340 / (NATO 5.56) - 1.2380 / (Difference) - 0.0040 Neck Length (.223 Remington) - 0.2200 / (NATO 5.56) - 0.2180 / (Difference) - -0.0020 Freebore Length (.223 Remington) - 0.0250 / (NATO 5.56) - 0.0500 / (Difference) - 0.0250 Rim/Belt Thickness (.223 Remington) - 0.2000 / (NATO 5.56) - 0.2000 / (Difference) - 0.0000 Shoulder Angle (Degrees) (.223 Remington) - 23.0 / (NATO 5.56) - 23.0 / (Difference) - 0.0 Throat Angle (Degrees) (.223 Remington) - 3.1 / (NATO 5.56) - 2.5 / (Difference) - -0.6
Dimensionally similar, but they are not exactly the same. A firearm with a 5.56x45 chamber can accommodate the .223 Remington cartridge, but a firearm with a .223 Remington chamber cannot accommodate the 5.56x45 cartridge.
You will have to call Remington with the serial number.
.223 inches in diameter, typically 45 to 55 grains for the .223 Remington, and 80 grains for the .223 Wylde.
If it has a dedicated .223 Remington chamber, you should not run 5.56x45 through it.
Only if it is marked ".223 Remington" on the barrel.