.223 Remington--Centerfire Favorite The .223 Remington is the most widely-used centerfire rifle cartridge in the developed world. In its 5.56x45 military form, it is the primary issue ammunition for the U.S. Military and NATO forces. It is a popular sporting cartridge, and probably the most commonly used centerfire varmint cartridge. In our Readers' Poll, the .223 Rem (both standard and improved) ranked first among preferred varmint rounds. The .223 Rem is efficient and versatile. It can sling 40-grainers past 3650 fps, and deliver 90gr VLDs accurately at 1000 yards. Its parent case, the .222 Remington, was once a mainstay of benchrest competition. Today, with custom match bullets, the .223 Remington can still deliver impressive accuracy, shooting well under quarter-MOA in a good rifle.
.223 Remington Cartridge History The .223 Rem traces its roots to the .222 Remington, a round popular with benchrest and varmint shooters in the 1950s. When the US military was looking for a new high-speed small-caliber round to replace the .308 Winchester (7.62x51), Remington started with the .222 Remington, and stretched it to increase powder capacity by about 20% in 1958 to make the .222 Remington Magnum. The cartridge was not accepted by the military, but it was introduced commercially. In 1964, the 5.56x45 mm, also based on a stretched .222 Rem case (and very similar to the .222 Rem Magnum), was adopted along with the new M-16 rifle. As with the .222 Rem Magnum, the new military case achieved enhanced velocity (over the .222 Rem) by increasing case capacity with a longer body section and shorter neck. This military modification of the .222 Rem was originally called the .222 Special but was later renamed the .223 Remington. In military metric nomenclature, the round is called the 5.56x45. For the full history of the 5.56x45 cartridge, read the 5.56x45 Timeline, by Daniel Watters.
.223 Remington vs. 5.56x45--Chambering and Throat Considerations Is the .223 Remington the same as the 5.56x45? The answer is yes and no. There ARE differences between the .223 Remington as shot in civilian rifles and the 5.56x45 in military use. While the external cartridge dimensions are essentially the same, the .223 Remington is built to SAAMI specs, rated to 50,000 CUP max pressure, and normally has a shorter throat. The 5.56x45 is built to NATO specs, rated to 60,000 CUP max pressure, and has a longer throat, optimized to shoot long bullets. That said, there are various .223 Remington match chambers, including the Wylde chamber, that feature longer throats. Military 5.56x45 brass often, but not always, has thicker internal construction, and slightly less capacity than commercial .223 Rem brass.
Should you be worried about shooting 5.56x45 milspec ammo in a .223 Remington? The answer really depends on your chamber. 5.56 x45 ammo is intended for chambers with longer throats. If you shoot hot 5.56x45 ammo in short-throated SAAMI-spec chambers you can encounter pressure issues. The new long-throated 'Wylde' chamber allows safe use of military ammo. Wylde chambers are quite common in Rock River guns. Other manufacturers, such as Fulton Armory, offer modified "match chambers" with extended throats that allow safe use of 5.56x45 ammo in .223 Remington rifles. For a complete discussion of the .223 Rem vs. 5.56x45 question, read this Tech Notice from Winchester, and this GunZone Commentary by Dean Speir. Without belaboring the point, we'll repeat the official SAAMI position: "Chambers for military rifles have a different throat configuration than chambers for sporting firearms which, together with the full metal jacket of the military projectile, may account for the higher pressures which result when military ammunition is fired in a sporting chamber. SAAMI recommends that a firearm be fired only with the cartridge for which it is specifically chambered by the manufacturer."
Twist Rates 223 Rem Remington barrel Twist rateThe .223 Rem shoots a wide range of bullets very effectively, from 35gr flat-based varmint bullets, to ultra-long 90gr VLDs. However, you'll need the right twist rate for your choice of bullet. For max velocity and accuracy with the lightest bullets, a 1:14" twist may be ideal. More versatile is a 1:12" twist that will allow you to shoot the popular 60-64 grain match bullets. (However, a 1:9" twist is needed for the steel-core 62gr bullet used in the M855 military loads, because that bullet is as long as most 70-grainers.) For normal lead-core jacketed bullets, a 1:9" twist will let you shoot up to 73gr bullets. Since most .223 Rem shooters prefer bullets in the 50-73gr range, a good "do-it-all" solution is a 9-twist, unless you're a Highpower competitor.
For long-range match purposes, long, high-BC bullets are favored for their ability to buck the wind. You'll want at least a 1:8" twist to shoot the 77gr and 80gr MatchKings and 80gr Bergers. To shoot the new 90gr pills, a 1:6.5" is recommended, though a true 1:7" will work in most conditions.
Overall, what twist rate is best? For varminting we like a 12-twist. The slower twist will give you a bit more velocity, and minimize the risk of jacket failure at high rpms. For general use, an 8-twist barrel will let you shoot the excellent 77gr and 80gr Sierra MatchKings and nearly all varieties of non-tracer milsurp ammo. We'd only select a 1:7" or faster twist barrel if we had a need to shoot the 90gr VLDs.