When it comes to rifle ammunition, the 5.56x45mm and .223 Remington cartridges are often compared and can cause confusion for shooters. While the two cartridges are similar in appearance and may fit in the same rifle, they are not interchangeable and using the wrong cartridge can cause damage to the gun or injury to the shooter. The main difference between the two cartridges is the pressure levels at which they operate. The 5.56x45mm cartridge is designed to operate at a higher pressure, which allows for longer ranges and more power. While the .223 Remington cartridge is designed to operate at a lower pressure, which makes it safer to use in rifles that are chambered specifically for .223 Remington. It also has thinner walls, which makes it more accurate at longer ranges. Therefore, it is important to check the caliber of your rifle and use the correct ammunition.