The .223 Wylde chamber is one of those epitomes of the concept of “happy” medium when it comes to shooting. It was born out of a need to balance engineering for accuracy and pressure. The dimensions of a firearm’s chamber, even with the exact same case dimensions, greatly affect how a gun will shoot.
The differences between the .223 Remington, 5/56x45mm NATO, and the .223 Wyle are based on two critical dimensions of the freebore, that smooth portion of the barrel between the case mouth before the rifling starts. The diameter of the freebore and the length of the leade make all the difference in the world.
| Chamber | Freebore Diameter | Leade Length | Maximum Pressure |
| .223 Remington | 0.2240” | 0.0250” | 55,000 psi |
| 5.56x45mm NATO | 0.2265” | 0.0566” | 62,000 psi |
| .223 Wylde | 0.2240” | 0.0619” | Under 62,000 psi |
The larger freebore diameter is what allow the 5.56x45mm NATO to go to higher pressures. But that wider diameter allows the bullet to obturate, wiggle just a little off axis, and that degrades accuracy as distance extents expressed as wider ballistic dispersion.
The .223 Wylde takes a different engineering approach. It keeps the freebore diameter smaller to control oburation and increases lead length to give just a little more expansion room for the gas as it ignites to keep the pressure under control.
The result is a chamber that is inherently more accurate and can handle 55 grain .223 Remington and M193 military ammunition, 62 grain M885/SS109 generation 5.56x45mm NATO STANAG ammunition, and, depending on the rifling twist rate, a new generation of heavy bullet .223 ammunition using projectile that weight between 75 to 85 grains.
One of the results is the stellar Mk262 Mod 0/1 77 grain BTHP ammunition that turns any 1-7 twist AR into an excellent designated marksman rifle. Taking advantage of the longer lead, another innovation is the arrival of 80 grain and heavier projectiles loaded longer than magazine length so that they jump around 15/1000th’s inch before contracting the rifling. These 80 grainers dominate the 600 yard stage of high power matches and, in combination with free floated handguards, have eclipsed the M-1 Garand and M-14/M1A in high-power competition. In the parlance of competition, these AR’s are hammers.
Evolution of the .223
The original .223 Remington was designed for light varmint bullets. Slow twists and 40 grain bullets came out very fast. Those light bullets were also short which meant the ideal freebore leade cut for those chambers also had to be short enough so that the front of the bullet jump that magic 15/1000thsin these varmint rifles. They also didn’t need as much twist rate to keep the bullet If you want a dedicated varmint .223 Remington, there’s still a lot to be said for a 1-14 twist barrel and a .223 Remington chamber.
During the Vietnam War era, the US adopted the M-16 series service rifle with the 1-12 twist barrel along with the M193 round. It had 55 grain full metal jacket boat tail bullet. The 55 grain pill was at the heavy end of the weight class of bullets for these barrels when it first appeared. They were just barely stable and would upset and tumble instantly upon impacting anything. This property is why what are called “Mattel” M-16’s, so named because the Mattel company produced a toy with the M-16A1’s distinctive triangle handguard, would produce pinhole entry wounds and stellate shaped exit wounds. The tumbling created hydrodynamic shock in wound cavity vastly amplifying the terminal ballistics effect of the weapon system in combat. The concept worked amazingly well prior to the arrival of effective body armor. Quite honestly, I would not consider myself under gunned even today with a 1-12 “Mattel” loaded with with a magazine of M193 FMJ’s.
By the 1970’s, armor changed the game. The arrival of the M-16A2, the need to penetrate brought about the M885 and SS109 ammunition with their 62 grain steel core bullets. This era also introduced other specialty ammunition for the M-16A2, notably longer bullet tracer ammunition for use in a new class of machine guns. As mentioned earlier freebore diameter and leade of the new 5.56x45mm NATO chambers we modified to manage chamber pressure and twist rate of the barrels was increase to 1 in 7 inches to stabilize the longest bullet and keep them flying true. This is a critical thing when you have a guy with an M249 Squad Automatic Weapon firing over the heads of advancing friendly personnel. You don’t want any of those bullets tumbling and falling short into your own troops.
One of the consequences of this was the M-16A2 generation of ball ammo is that it is over stabilized in a 1-7 twist barrel. It flies too true . It lost the devastating tumbling terminal effects of the Vietnam guns. The M855 and SS109 ammo did indeed penetrate. It made a pinhole going in and a pinhole going out. In the civilian world, people experimented in 1-9 twist rate barrels to slow the spin rate of the bullets. These 1-9 barrels are designed specifically to work with 62 to 70 grain projectiles and they work very well if all you will shoot our of your AR is 62 grain ammo.
Competition Drives Innovation
Civilian innovators continued to improve the .223 to make it even more accurate. played around with this. People liked the 1-7 twist barrel but it was clear that the bullet weight needed to be increased. Beginning in the mid-1990’s, heavier bullet designs began to appear. New 75 and 77 grain bullets that could be loaded to magazine length appeared. Long 80 grain bullets also appeared that could be loaded long shortening the jump back to the magic 15/1000ths inch to the rifling. These bullet innovations greatly increased accuracy by bringing the spin stabilization of the ammunition closer to ideal, which means that the axis of the bullet align with the path of flight better. Super-stabilized bullets start to fly at a crab angle the further out you go. Longer bullets like the 80 grainers control for jump which minimizes obturation which further enhances accuracy.
The thing about all this bullet work was that people were still living within the limitations of choosing either a .223 Remington chamber or a 5.56x45mm NATO one. It was inevitable that wildcatters would start to experiment. You can machine a chamber reamer to do anything you want. And that’s how the Wylde chamber was born. It took the best of the .223 Remington, the 5.56x45mm NATO, and 1-7 twist class bullets, and created a tack driver.
Bear in mind that accuracy doesn’t last. Competition barrels are like tires, they wear out and you change them. The rule of thumb is that a barrel lasts between 3 to 5 seconds of total burn time before the throat erodes to the point that accuracy starts to suffer if your objective is to send every round into the X ring.
In a competition tuned AR-15, it produces a barrel that can shoot 69 to 77 grain class magazine length ammunition well out to 300 yards for between 3,500 to 4,500 rounds with good accuracy. The thing to watch is the rapid prone stage of a high-power rifle match.
Provided your hold is good enough to shoot at the X-ring, you can watch a walnut pattern grow into a tangerine pattern as the barrel wears out. Do not let the patten grow to the size of an orange. Typically, a service rifle competitor will change barrels once a year. That’s considerable shorter life than the 10,000 to 15,000 round rated lifetime of a barrel used to other types of shooting.
For shooting put to 600 yards, the name of the game is to chase the barrel erosion seating your heavy 80 to 85 grain bullets further out to maintain the jump at the ideal 15/1000ths inch jump. Your magazine length ammo pattern at 300 will have gone south well before you run out of room seating your long line ammo.
There are other .223 chambers for even more specialized applications. If you want to shoot magazine length ammunition only, there are versions of chambers that have the shorter leades. There are also variations where the chamber reamer dimensions at the back of the base are more generous to accommodate reloaders who do not wish to used a small base sizer die and maintain high reliability.
But they are all variation on the innovation of the .223 Wylde. Give one a try and see just how much performance you can get out of America’s modern sporting rifle.