Rambling thoughts on 223 Remington vs 5.56 NATO Chambers
by Greg Ritchie
[5.56 specifications - This file is licensed under the Creative Commons Attribution 3.0 Unported license by Francis Flinch]
The .223 Remington and 5.56 NATO cartridges are by all outward appearances identical. Why then, the difference in chambers?
The 223 Remington was SAAMI (Sporting Arms and Ammunition Manufacturers' Institute) approved in the early 1960's. As a SAAMI cartridge, chamber dimensions are dictated by SAAMI specifications. The leade or throat of a SAAMI .223 chamber is about half as long and tighter bored than a NATO 5.56 chamber.
The leade is the section of the chamber from the mouth of the cartridge case to where the rifling starts. The difference in the leade dimensions is a contributing factor in the notion that a rifle chambered in 5.56 is not as accurate as one chambered in .223. The longer and larger lead of the 5.56 chamber allows wiggle room for the bullet in its travels from the case mouth to the rifling. This can allow the bullet to get to the rifling without being concentric to the bore.
Another consideration for the handloader is that it is common practice to load a cartridge to the point that the ogive of the bullet is just a few thousands from contacting the rifling. This minimizes the possibility of the bullet not being concentric to the bore when fired. This is not a problem unless an individual owns both a .223 and a 5.56 chambered rifle. Then care must be taken to keep the cartridges separate. A round loaded specifically for a 5.56 chambered rifles will cause pressure issues if fired in a .223 chamber. Such a round, if chambered then extracted without firing will usually leave the bullet stuck in the bore and the powder dumped into the action.*
This brings us to the Wylde and Noveske chambers. These chambers are effective attempts to fix the accuracy problems associated with the 5.56 NATO chambers. The Wylde is probably the most common. It is basically throated with the leade of the NATO chamber and the diameter of the .223 Remington chamber. It is effective in keeping the bullet concentric with the bore.
Notice that I have not mentioned anything about the pressures the cartridges are loaded to. There is said to be a significant increase in pressure with the NATO round vs the SAAMI round. On the surface this appears to be true. However the pressure is measured in a very different way. NATO measures the pressure at the case mouth. It is my understanding that the pressure can vary significantly on identical cartridges just because of the method of measuring. What I am sure of is that a cartridge jammed into the rifling before being fired can increase pressure significantly. Therefore I will err on the side of caution and not fire 5.56 in a .223 chamber.
So which chamber would I choose? I see little reason for a .223 Remington chamber, although I do own one. I am very fond of the .223 Wylde chamber and that is my preferred chambering. But for the individual who is just going to own an AR style rifle and is not interested in extreme accuracy, the 5.56 would be my choice. It will fire both .223 and 5.56 without concern and while maybe not as accurate as the Wylde chambering, it is accurate enough. Maybe not groundhog accurate at 400 yards, but certainly accurate enough for 90% of what the rifle will be called on to do.
*Editor's Note: Specifically hand-loaded cartridges optimized by Over All Length (OAL) for a 5.56 NATO chamber because of the difference in distance the leade (distance to the rifling). Under these circumstances, a hand-loaded and 5.56 NATO optimized OAL cartridge will almost certainly prematurely contact the rifling when inserted in a .223 Rem. chamber, which will cause pressure spikes that could be dangerous.