5.56 vs. .223: Which Can I Shoot?

By Wayne van Zwoll

Posted in
#Gear

Many shooters view the .223 and 5.56 as identical or at least interchangeable rounds. Well, listed case dimensions are the same, and each will chamber in barrels bored for the other. But that’s not the full story.

Do you own an AR like this SAINT? Do you know what ammo to load in it?

Hornady engineers tell me the .223 Remington is stoked to 55,400 CUP (Copper Units of Pressure), a level specified by SAAMI (the Sporting Arms and Ammunition Manufacturers Institute). Service loads for the 5.56×45 NATO generate 58,500. Chamber dimensions and rifling twist vary among the myriad AR-15s and bolt rifles barreled to .223, but the 5.56 commonly gets a longer throat. “Roughly .125 more freebore,” say the white-coats bearing micrometers.

Can You Shoot .223 in a 5.56 Rifle?

It is generally accepted that commercial .223 Rem ammunition like the Norma Tactical .223 can be safely shot in any firearm chambered for the 5.56 NATO cartridge. However, given common differences in loads and throats, it’s a good idea not to use 5.56mm ammo in a firearm with a dedicated .223 chamber.

In 1979, SAAMI cautioned that 5.56 chambers differ from those in .223 sporting rifles, and that use of 5.56 ammo in .223 rifles could jack pressures to unsafe levels. The reverse — .223 in a 5.56 chamber — doesn’t have the same pressure concerns.

So what does that mean for your firearm?

In the case of Springfield Armory’s SAINT .22-bore rifles and pistols, they are described as “multi-caliber”, meaning they’re designed to function well and safely with both .223 and 5.56mm rounds.

Two cartridges positioned side-by-side display the visual comparison between 5.56 NATO ammunition (left) and .223 Remington ammunition (right), with the 5.56 NATO round clearly showing the distinctive crimped primer annulus that differentiates military-specification cartridges from commercial sporting ammunition. The primer crimp on the 5.56×45 NATO cartridge serves as a military requirement to prevent primer displacement during automatic fire and rough handling in combat conditions, while the .223 Remington typically lacks this feature for civilian sporting applications. Both cartridges share identical external case dimensions of 1.76 inches in length, yet the 5.56 NATO operates at higher chamber pressure of 58,500 CUP compared to the SAAMI-specified 55,400 CUP rating for .223 Remington loads. The case head stamps and overall appearance demonstrate why many shooters mistakenly consider these cartridges completely interchangeable, though critical differences in chamber specifications, freebore length (approximately .125 inches longer in 5.56 chambers), and pressure ratings make safe interchangeability directional rather than universal. This visual identification guide helps AR-15 owners and bolt-action rifle shooters distinguish between military 5.56mm Ball cartridge M193 or M855 ammunition and commercial .223 Rem hunting or target loads before chambering rounds. The comparison illustrates that while .223 Remington can be safely fired in 5.56 NATO chambers, the reverse combination of firing 5.56 NATO ammunition in dedicated .223 chambers may generate unsafe pressure levels as cautioned by SAAMI in 1979. Understanding these visual differences between fraternal twin cartridges prevents potential overpressure situations and ensures proper ammunition selection for rifles chambered in either specification. The image serves as essential reference material for shooters selecting appropriate ammunition for their specific firearm's chamber designation, whether for Springfield Armory SAINT multi-caliber rifles or traditional bolt-action varmint rifles. — Are they the same? Here the 5.56’s crimp distinguishes it (at left).

.223 vs. 5.56: Fraternal or Identical?

The lineage of these enigmatic twins dates to 1957, when the .223 popped up as an experimental cartridge for what would become the M16 infantry rifle. Working with Gene Stoner, Bob Hutton at Guns & Ammo magazine paired a 55-gr. bullet with a case a tad longer than a .222’s cartridge case. The tiny missile exited at 3,250 fps and met a retained-velocity spec of supersonic flight to 500 yards.

Adopted in 1964 as the 5.56mm Ball cartridge, M193, it was issued to U.S. forces in Vietnam, and after that tour until 1984. In 1980 it earned the approval of NATO nations, which substituted an FN-designed 62-grain SS109 boat-tail bullet. The SS109 left the gate at 3,100 fps. Its superior ballistic coefficient ensured harder hits at distance. Faster 1-in-7 rifling twist maintained accuracy. The U.S. Army called this load the M855. By then, case length in millimeters had joined the moniker. So was born the 5.56×45 NATO.

Hornady TAP (Tactical Application Police) ammunition boxes and cartridges displayed in both 5.56×45mm NATO and .223 Remington chamberings demonstrate the manufacturer's precision loading standards for law enforcement and tactical applications across both cartridge specifications. The Hornady ammunition lineup shows the company's thirteen different .223 Remington load offerings that range from 35-grain NTX bullets achieving 3,760 fps velocity to 75-grain Superformance Match BTHP projectiles traveling at 2,930 fps for long-range accuracy. Hornady's engineering specifications confirm that .223 Remington operates at SAAMI-approved 55,400 CUP pressure levels while 5.56 NATO service loads generate higher 58,500 CUP chamber pressures, requiring careful attention to proper cartridge-to-chamber matching. The TAP series ammunition represents Hornady's commitment to barrier-blind performance and consistent expansion in both military-spec 5.56mm chambers with longer freebore and commercial .223 chambers with tighter tolerances and shorter throat dimensions. These cartridges feature boat-tail hollow point projectiles similar to the 62-grain SS109 bullet design adopted by NATO forces in 1980, which replaced the original 55-grain M193 Ball cartridge with superior ballistic coefficient for enhanced downrange performance. The ammunition packaging clearly identifies each cartridge designation to prevent confusion between the two specifications, addressing the critical safety concern that firing 5.56 NATO rounds in dedicated .223 chambers could elevate pressures to dangerous levels. Hornady's quality control and pressure testing ensure reliable function in AR-15 platform rifles, bolt-action varmint rifles, and multi-caliber capable firearms like the Springfield Armory SAINT series. This comparison illustrates the commercial ammunition market's response to shooter demand for both tactical law enforcement loads and precision sporting ammunition in America's most popular rifle cartridge family. — Popular 55-gr. loads can shoot well from a 1-in-12 twist. A faster spin helps with longer bullets.

It was soon recognized that the round had a lot of merit for use in sporting rifles. Naturally. The .223’s design owed much to the popularity of the .222 Remington round that had been introduced in 1950. The “triple deuce” cleaned up at Benchrest meets and bumped pelt counts for fox hunters. The .223’s 1.76″ case is just .06 longer than the .222’s. But the .223 has a shorter neck and holds 20 percent more powder.

As rifles and loads were developed for the new .223 round, a shorter throat and steeper leade (ramp angle of the lands in front of the throat) was employed. A tiny rodent behind the crosswire demanded fine accuracy not required on the battlefield. An infantry rifle’s priority was function, often in trying conditions hunters didn’t endure. No matter the weather, the grit and debris and egg-cooking barrel temperatures, perhaps long-nose tracer bullets awaiting their chance to jam, a soldier needed the bang!

Three rifle cartridges arranged in ascending size order demonstrate the compact dimensions of the .223 Remington and 5.56 NATO compared to the larger 6.5 Creedmoor cartridge, illustrating how the .223's relatively short 1.76-inch case length was specifically designed for more compact rifles and intermediate-caliber applications. The .223 Remington cartridge positioned on the left shares identical external case dimensions with the 5.56×45 NATO round in the middle, both descended from the .222 Remington "triple deuce" introduced in 1950 for benchrest shooting and varmint hunting applications. The 6.5 Creedmoor cartridge on the right towers over both .22-caliber rounds, emphasizing the design philosophy differences between intermediate rifle cartridges developed for the M16 military rifle platform and modern long-range precision cartridges optimized for target shooting and big game hunting. This size comparison reveals why the .223 case holds approximately 20 percent more powder than its .222 Remington predecessor despite being only .06 inches longer, achieving velocities of 3,250 fps with 55-grain bullets as specified in the original experimental cartridge development by Gene Stoner and Bob Hutton at Guns & Ammo magazine in 1957. The visual scale difference illustrates ammunition selection considerations for AR-15 rifles versus bolt-action platforms, with the compact .223/5.56 cartridges designed for semi-automatic and automatic fire functionality while the 6.5 Creedmoor represents traditional sporting rifle cartridge proportions. Understanding cartridge dimensions helps shooters appreciate why .223 chambers feature specific throat lengths and leade angles different from 5.56 NATO military specifications, with the latter incorporating approximately .125 inches more freebore to accommodate higher 58,500 CUP pressure levels versus the SAAMI-specified 55,400 CUP for commercial .223 Remington loads. The comparison also contextualizes the .223's popularity for prairie dogs, coyotes, and where legal for deer hunting, offering sufficient case capacity for versatile bullet weights from 35-grain varmint projectiles to 75-grain match bullets without the recoil and barrel wear of larger cartridges like the 6.5 Creedmoor. — The .223 is a relatively short cartridge designed for more compact rifles. It is shown here with the larger 6.5 Creedmoor.

As a result, M16s got generous chambers. Bolt-action rifles enjoyed tighter tolerances, shorter bullet jump and slower 1-in-12 rifling for popular 40- to 55-gr. varmint bullets. But, today’s AR’s in the civilian market have proven to be extremely capable of impressive accuracy as well.

No Looking Back

The .223 has piled up a mountain of commercial loads as compared to relatively few of the 5.56 NATO. Winchester alone lists 18! Remington has 13. So does Hornady, from a 35-gr. NTX bullet at 3,760 fps to a 75-gr. Superformance Match BTHP at 2,930. Federal catalogs a dozen .223 loads, including a 60-gr. Nosler Partition at 3,160 fps and a 62-gr. Trophy Bonded Tip at 3,050. Swift loads a 75-gr. Scirocco. Black Hills Ammunition rips tons of ballistic gelatin refining .223 loads (15) and 5.56 (8), as it supplies U.S. troops with mil-spec 5.56.

A precision shooting target displaying tight shot groups demonstrates the exceptional accuracy potential achievable with quality .223 Remington and 5.56 NATO ammunition when fired from properly configured AR-15 rifles or bolt-action platforms with appropriate rifling twist rates and chamber specifications. The small group clusters on the target paper validate that today's civilian market AR-15 rifles have proven extremely capable of impressive accuracy performance, dispelling outdated notions that only bolt-action rifles with tight tolerances and shorter bullet jump could achieve benchrest-grade precision with .22-caliber cartridges. This accuracy testing result reflects the importance of matching ammunition specifications to barrel characteristics, with 1-in-12 twist rifling stabilizing popular 40- to 55-grain varmint bullets while faster 1-in-8 or 1-in-7 twist rates accommodate heavier projectiles up to 80-grain boat-tail hollow points for long-range match shooting. The target groups illustrate why proper ammunition selection matters for optimal performance, as .223 Remington commercial loads with their shorter throat and steeper leade angle can deliver sub-MOA accuracy in dedicated .223 chambers, while 5.56 NATO ammunition with longer freebore specifications performs best in military-spec chambers or multi-caliber capable rifles like the Springfield Armory SAINT series. Companies like Black Hills Ammunition conduct extensive accuracy testing with both .223 loads (15 offerings) and 5.56 NATO rounds (8 offerings) to refine ballistic performance for civilian shooters and military applications, with rigorous evaluation in ballistic gelatin and on precision targets. The demonstrated accuracy validates the .223's evolution from its M16 military roots and original 1957 experimental cartridge design to become a dominant force in competitive shooting, varmint hunting, and tactical applications where sub-inch groups at 100 yards are routinely expected. This testing comparison helps shooters understand that with proper rifle setup, quality ammunition from manufacturers like Hornady, Federal, Winchester, or Remington, and correct rifling twist rates, both .223 Remington and 5.56×45 NATO cartridges can deliver outstanding accuracy regardless of their different pressure specifications and chamber dimensions. The tight shot groups on target prove that the choice between .223 and 5.56 NATO need not compromise precision when shooters understand proper cartridge-to-chamber compatibility and select appropriate bullet weights for their barrel's twist rate. — Tiny groups like these are very possible with quality ammo and a good rifle.

The .223’s credentials on prairie dogs and coyotes hardly need defending. But where it’s legal for deer, hunters debate. Two-two-three acolytes dig out ballistics charts. “The .44-40 has laid low countless deer with 200-gr. bullets that bring 450 ft-lbs to 100 yards. Winchester’s 64-gr.Power-Point — hardly the frothiest .223 load — delivers 1,000 ft-lbs there and trumps the bullet weight/animal weight and bullet energy/animal weight ratios of 175-gr. 7mm Magnum bullets on elk!” The advent of stoutly built .22 game bullets like Remington’s Core-Lokt Ultra Bonded, Nosler’s Partition, Hornady’s GMX and Swift’s Scirocco argue in favor of the .223’s use on deer.

A counterpoint: Bullet weight and diameter bow to velocity in energy calculations, but can figure heavily in killing effect. Arguably, precise shot placement matters most with small bullets.

The wide range of .223 loads begs sifting before you specify rifling twist. Nosler advises a 1-in-12 spin for bullets no longer than its 60-grain Partition. In my tests, 1-in-12 bores kept groups tight with bullets as heavy as 62 grains but spun 69-grain BTHPs too slowly. A 1-in-8 spin is claimed to stabilize BTHPs to 80 grains, and shoot bullets as light as 50 grains accurately. As always, test out your preferred load in your gun to check results.

Ballistic gelatin blocks displaying wound channel characteristics and bullet expansion patterns reveal the terminal performance differences between .223 Remington hunting ammunition and 5.56 NATO military loads, with Black Hills Ammunition conducting extensive gelatin testing to refine both commercial sporting loads and mil-spec 5.56 ammunition supplied to U.S. troops. The gelatin test results demonstrate penetration depth, temporary cavity formation, and projectile behavior after impact, illustrating why bullet selection matters significantly for applications ranging from prairie dog and coyote hunting with .223 Remington to defensive and tactical scenarios with 5.56×45 NATO loads. This terminal ballistics comparison shows how stoutly built .22-caliber game bullets like Remington's Core-Lokt Ultra Bonded, Nosler's 60-grain Partition, Hornady's GMX monolithic copper projectiles, and Swift's 75-grain Scirocco deliver controlled expansion and deep penetration suitable for deer hunting where .223 Remington is legally permitted for big game. The gelatin testing validates that Winchester's 64-grain Power-Point .223 load delivers over 1,000 foot-pounds of energy at 100 yards, exceeding the performance of the historic .44-40 cartridge that successfully harvested countless deer with 200-grain bullets producing only 450 foot-pounds at similar distances. Military 5.56 NATO projectiles including the 62-grain M855 SS109 boat-tail bullet and 55-grain M193 Ball cartridge exhibit different wound channel characteristics due to their higher velocities and construction designed for barrier penetration and fragmentation rather than controlled hunting expansion. The visual evidence in ballistic gelatin underscores the ongoing debate about .223 Remington adequacy for deer hunting, with proponents citing favorable bullet weight-to-animal weight ratios and energy delivery that trumps larger calibers when calculated by standard formulas, while critics emphasize that bullet diameter and sectional density matter beyond raw velocity-driven energy calculations. Black Hills Ammunition's rigorous testing of fifteen .223 Remington loads and eight 5.56 NATO offerings demonstrates the manufacturer's commitment to understanding real-world terminal performance across both cartridge specifications for civilian and military applications. This ballistic gelatin comparison helps shooters understand that precise shot placement matters most with small-caliber bullets, and that modern .223 hunting bullet designs with bonded cores and controlled expansion technology have significantly enhanced the cartridge's effectiveness on game animals beyond the original 55-grain military full metal jacket projectiles. — Black Hills Ammunition tests 5.56 loads for terminal performance in gelatin, as well as for accuracy. Image: Black Hills Ammunition

Conclusion

So there you have it, the story of the .223 vs. 5.56, going back to the birth of the 5.56mm M16 all the way up to today’s top .223 loads. Obviously, the round and the AR combo is one of the most popular in American today, due in no small part to the exceptional performance of both.

Much like the 7.62 and .308 rounds, there is sometimes confusion over what each cartridge designation means. Are they the same, or are there significant differences.

The .223 has grown beyond its M16 roots to become a popular round for other platforms such as bolt-actions and more. And now you know what you can shoot in which!

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