The year is 1956 and Eugune Stoner is leading a team of engineers while working for ArmaLite Rifles, a sub-division of Fairchild Aviation. Eugene Stoner had previously designed the AR-10, a battle rifle chambered in .308 Winchester, but is now downsizing it into the AR-15.
The AR-15 is technically a .22 caliber rifle. AR-15s in common use today shoot .224 caliber bullets. The AR-15 was originally chambered in .222 Remington, but soon after release it changed to shoot the more powerful .223 Remington. The 5.56x45mm standard was used when adapted for military use. Despite all the different chamberings, these all shoot the same, .224 caliber bullet.
Since the late 50s and early 60s, the AR-15 has been chambered in calibers ranging from .17 to .50, but at its heart, it’s a .22 caliber rifle. The most common chamberings for the last few years have been 5.56x45mm and .223 Wylde.
The AR-15 was originally chambered in the now-obscure .222 Remington. It was introduced in 1950 and was sold as a low-recoil, varmint, and target cartridge. Rifles chambered in this cartridge used a 1:14 twist, something that is only suitable for light-weight bullets.
While the .222 Remington still exists, there is no reason other than nostalgia to buy a rifle chambered in it. Its successor, the .223 Remington, is the all-around better cartridge.
In an effort to give the .222 Remington more power, the shoulder of the case was moved forward and the neck was shortened. This gave the case more powder capacity. The maximum chamber pressure was also increased from 50,000 PSI to 55,000 PSI.
This creation was originally called the .222 Special but was renamed the .223 Remington to avoid any confusion. Colt’s Manufacturing Company, LLC, commonly referred to as just Colt, bought the rights to the AR-15 from ArmaLite and the rifle was chambered in this cartridge when the US Air Force took an interest in it.
In the modern era, .223 Remington is by far the most used cartridge in the AR-15. However, very few AR-15s have been chambered in this cartridge for the last 10-15 years.
When the US Airforce adopted the M16 rifle, which itself is a slightly modified AR-15, the decision to chamber it in the 5.56x45mm was made. Externally, the 5.56x45mm and the .223 Remington are identical. In factory ammo, only looking at the headstamp or packaging will let you know the difference.
The 5.56x45mm is slightly more powerful than the .223 Remington and has a slightly higher chamber pressure (55,000 PSI vs 62,350 PSI). To assist with the higher pressures, the 5.56x45mm chamber is slightly modified. Because of this, a 5.56x45mm chambered AR-15 can shoot both .223 Remington and 5.56x45mm cartridges.
It is not recommended to shoot 5.56x45mm ammunition out of AR-15s chambered in .223 Remington, as it can lead to unsafe pressures. 5.56x45mm is also commonly referred to as 5.56 NATO or just 5.56.
The .223 Wylde, unlike the previously discussed cartridges, is only a chambering. There has never been, and will never be .223 Wylde ammunition. Rather, it is an adaptation of the .223 Remington and 5.56x45mm chambers. Its goal is to be more accurate than the 5.56x45mm chambered barrels.
It’s long been known that barrels for AR-15s, both in 5.56x45mm and .223 Remington are all over the place in terms of dimensions. Part of this comes from the fact there are so many different manufacturers of these barrels, and part of it is the popularity of lower-priced ARs.
To be clear, budget ARs aren’t bad, but there isn’t a big push for precision at the bottom of the market.
The goal of the .223 Wylde is to make the tightest chamber that can still shoot the more powerful 5.56x45mm ammo. The chambering isn’t that old, less than 10 years, but it has become very popular.
Which .22 Caliber Chamber is the Best?
The simple answer is you should only consider a .223 Wylde or 5.56x45mm. Unless you have very specific needs, there is no reason to consider buying an AR-15 in .223 Remington in the year of our Lord 2021. Many manufactures have altogether stopped offering them as well.
But is one better than the other? I generally say no. In the technical sense, the .223 Wylde barrel should be more accurate and the 5.56x45mm barrel should be more reliable. In real-world practice, I don’t think you’ll ever notice a difference.
There are high-quality 5.56x45mm barrels that will outshoot almost all .223 Wylde barrels, so unless you are buying the absolute best of the best, overall accuracy is far more than just the chambering. I have also never seen a reliability issue with a good .223 Wylde barrel, and only heard one experienced shooter say they have.
My general advice is to pick the length, profile, material, and treatment you want in a barrel before you even consider .223 Wylde and 5.56x45mm chamberings.
Lets Talk Barrel Twist
The AR-15 has used a variety of different barrel twists over the years. For those new to firearms, the twist rate is measured by how many inches does it take for a bullet to make a full revolution while traveling down the barrel. For example, a 1:7 barrel will spin a bullet once every seven inches. I have seen AR-15 barrels with twist rates from 1:14 to 1:6.
1:14 Twist: This is the original twist rate of the AR-15 but these days is very uncommon. It is useful for very lightweight bullets and 55-grain FMJBT bullets. I don’t know of any factory AR-15s that come with barrels in this twist rate. These days, this twist rate is primarily used for nostalgia builds.
1:12 Twist: When the US Airforce adopted the M16 as a service rifle, it changed the twist rate of the barrels to 1:12. In practical use though, there is a minimal difference between 1:12 and 1:14. They will both shoot 55-grain FMJBT bullets and lighter, but not the common M855 “green tip” ammo. These are primarily used for nostalgia builds and dedicated varmint guns.
1:9 Twist: Before the AR-15 became a popular rifle, many of the rifles meant for civilian use had 1:9 barrels. This was deemed the ideal twist rate for shooting 55-grain FMJBT ammo and the longer 62-grain M855 ammo. This twist will also stabilize most of the 69-grain match bullets and some barrels will stabilize the 75 to 77-grain match bullets.
In the past 10 years though, this twist length has seen a huge decrease in popularity as long and heavy match bullets have become more popular. 1:9 has also become synonymous with the word “cheap” in the AR world.
Truthfully, I think this twist rate is fine for 95% plus of AR-15 buyers, but there is no compelling reason to buy a new AR-15 barrel in 1:9. The M855 ammo it was designed to shoot is trash and uses one of the least accurate modern bullets around.
1:8 Twist: This is the new trendy twist rate for “precision” AR-15s, along with 1:7.7 to a much smaller degree. Barrels with a 1:8 twist will stabilize any .224 bullet that can be seated short enough to fit in an AR-15 magazine. As a result, it is a very good choice and has become very popular.
1:7 Twist: When the M16A2 was introduced, 1:7 became the military standard for twist rate. Although regarded for civilians as over-kill, it works perfectly fine for a very wide variety of bullet weights. Even with lightweight bullets, like 40-grain varmint bullets, it can produce excellent accuracy as long as the bullet is meant for high velocities. It is still quite popular and another excellent choice for general users.