What is the difference between 223 Remington and 556 NATO Ammo?

What is the difference between 223 Remington and 556 NATO?

There is a whole lot of confusion out there regarding these 2 rounds. Below are some of the reasons why.

1. Pressure. The most important difference of the 223 & 556 is pressure. The 5.56 NATO round produces more pressure than the .223 Remington. This has confused many people in the past for a variety of reasons, one of them being the fact that 223 meets SAAMI standards, and SAAMI measures pressure at the center of the casing. The 556 on the other hand complies with NATO standards who measures pressure at the leade of the chamber. The bottom line here is that 556 produces more pressure and not all rifles are built to handle the pressure.
2. Chambers. .223 Remington chambering is also known as a SAAMI chamber. SAAMI chambers are pressure tested to SAAMI specifications. NATO (aka mil-spec) chambers are tested to NATO specs and also have a longer leade. Firing 556 through a 223 leade can generate pressure which exceeds SAAMI maximums potentially resulting in a variety of failures.
3. Rifles. Some 223 rifles have SAAMI spec chambers. Other 223 rifles can safely handle 556. Variations exist in some models such as the Ruger Mini-14. The Ruger Mini-14 target model, for example, is chambered for 223 only, while other Mini-14s may shoot 556. (Most have 5.56 printed on the barrel).  
4. Manuals. Some rifles which can safely shoot 556 state they can only shoot 223 in their owner’s manual. This leads to confusion as some people shoot 556 through their 223 without a problem and then assume all 223 can shoot 556 or assume that it can be done long term without any problems; this is not true.
5. Guns chambered for 556 can shoot 223, but, as described above, not all 223 should shoot 556.

There are many other differences between the .223 Remington and the 5.56 NATO. Above are simply the most important safety reasons.

We carry a variety of 223 & 556 here: 223 Remington and 556 NATO ammo.