338 ARC: The Big Little Cartridge That Packs a Punch

Hornady’s 338 ARC Is a Revolution in Cartridge Theory

My first impression of the 338 ARC was that it promised pure, projectile-based fun. From the diminutive Grendel case to the oversized bullet, everything about it looked like each primer ignition would bring a smile. While fun is an important part of the equation, the introduction of the 338 ARC signifies a foundational shift in ballistics thought — specifically in the subsonic realm.

Before we continue, let’s have a primer on subsonic cartridges. The term subsonic means anything below the speed of sound. The speed of sound is 1,125 fps (760 mph). The whole point of subsonic ammunition is the lack of a “crack” when fired. Seems straightforward, right? In some ways, yes, but there are some variables to watch.

The speed of sound can be affected by environmental factors. Things like ambient temperature, elevation and air density can all influence that magical number. With that in mind, creating a round that is truly subsonic regardless of external variables is a blend of engineering, innovation, and ballistic alchemy.

THE HISTORY

The idea for this chambering began in 2016, when the Department of Defense approached Hornady to address a need. DOD asked Hornady to increase the terminal performance and effective range of subsonics. The best-known subsonic cartridge was the 300 Blackout, which did not deliver the level of performance the DOD desired in either range or energy.

The parameters of subsonics at the time were confined to an effective range of 50 to 75 yards. The desired goal was somewhere in the 200- to 300-yard range. With that in mind, Hornady started with the already DOD-approved Grendel case. There are a few reasons for this selection we will cover shortly. The development of the working cartridge, the 338 Advanced Rifle Cartridge (ARC), led to testing a viable subsonic bullet — a 315-grain projectile. While it performed well, the 338 ARC didn’t go any further. In the meantime, Hornady developed and launched two other cartridge offerings in the ARC family — the supersonic 6 ARC and the 22 ARC. 

The Advanced Rifle Cartridge label includes a few key points. Cartridges bearing ARC in their headstamps have been designed to maximize ballistic performance. It means the chamber/cartridge interface, bullet specifications, current firearm, and magazine constraints and consistency are considered in the engineering process. Theoretically, the cartridge must perform accurately and reliably in firearms of vastly different price points. Whether shooting an off-the-rack Tikka or a custom system from Gunwerks, the expectation is that the ammunition will perform well in both. 

Interest in the 338 ARC was rekindled when the subsonic market began to take off, mainly due to the 300 Blackout and 8.6 BLK. The 300 Blackout shone in the 180-grain subsonic realm with a recommended 1:8 barrel twist to stabilize long, heavy bullets. It was both fun and versatile, but its range was limited, and bullet weights were maxed out. 

The 8.6 took a different route. Based on a 6.5 Creedmoor case, it was trimmed and necked up to accommodate a .338-caliber projectile. The 8.6 was designed to run in either a short-action bolt gun or an AR-10. The efficacy of this caliber revolved around the “Blender Effect.” Utilizing a 1:3 or 1:4 twist, terminal effectiveness was achieved by rapidly spinning a large bullet at subsonic speed. 

Its effective range is reportedly around 300 yards. However, the 8.6, while popular in its niche, has had some struggles. The case capacity results in narrow velocity ranges when powder burn rates and pressures are considered. As a result, chambering can be picky, making repeatable, consistent performance a challenge.

Additionally, the 8.6’s fast barrel twist rate creates extreme barrel RPM, meaning bullet construction and quality must meet a zero-tolerance threshold for imperfections. Any flaw at high rotations-per-minute speed can create catastrophic bullet failure, which can lead to missed or botched shots downrange, or, more worrisome, firearm or suppressor damage.

Also, one of the outcomes of the 8.6’s extremely fast twist is that only monolithic projectiles can be used. Additionally, the shooter is confined to only shooting subsonic loads from a particular gun/barrel due to the twist.

So those issues set the performance parameters for the subsonic-cartridge market. The time had come to begin distilling Hornady’s 338 ARC into a finished product.

THE PROBLEMS IT FIXES

In 2016 to 2017, DOD asked Hornady to make a longer-range, high-performing subsonic round with better terminal effectiveness than the 300 Blackout or 8.6 Blackout. 

In supersonic rounds, increasing energy is generally straightforward: increase the bullet’s speed. With subsonics, increasing energy gets a little trickier because maximum speed is fixed. For subsonics, the only way to increase energy is to increase bullet weight. The caveat is that the bullet must expand to maximize its terminal effect.

Hornady uses the variables of shape, materials, and construction to create “the bullet” for a specific chambering. The actual weight of the bullet is often considered almost a postscript, with shape the driving factor in performance. In 2016, the bullet undergoing testing was a subsonic 315-grain cup-and-core type. 

While the performance was good, it wasn’t the finished round brought to market when the 338 ARC actually launched in 2024. Instead, Hornady introduced the 307-grain Sub-X in the 338 ARC. The Sub-X is a cup-and-core design with the Hornady FlexTip. In the 338 ARC, the Sub-X towers above its compact Grendel case.

THE POWDER PROBLEM

Below the big Sub-X projectile was another inherent issue with subsonics: finding a powder that burns consistently, thoroughly, and efficiently. Given the desired parameters of longer-range terminal effectiveness, powder performance was especially critical. 

To solve this problem, Hornady formulated a cocktail of good ignition from a very small propellant charge. The compact Grendel case was a perfect environment for quickly building the pressure needed to propel the 307-grain bullet out the end of the barrel. Operating pressure was a safe 52,000 psi. The propellant blend is also consistent and stable across broad temperature ranges, correlating with higher performance downrange. To stay subsonic in all conditions, Hornady opted for a muzzle velocity below 1,100 fps. 

IN THE FIELD

Hornady also wanted stability and acceptance by barrel makers. Accordingly, the 307 Sub-X is optimized for a 1:8 twist, producing smooth, consistent bullet travel and allowing for better bullet integrity before and after reaching the target.

Hornady’s approach to subsonic twist rates achieves a couple of things. First, it allows for broader usage of the same gun. Instead of being pigeon-holed into heavy-for-caliber subsonic bullets, the shooter can also employ supersonic rounds with the same expectation of accuracy and precision. So, Hornady brought a 175-grain hollowpoint in 338 ARC to market at the same time as the big-boy 307. Second, a common barrel twist opens the door to the manufacture of more affordable rifles. Instead of having to custom-build a 338 ARC rifle, there are off-the-rack options to enjoy the fun and performance of the round.

The 338 ARC was designed for either a micro-action bolt gun or an AR-15 platform — a new frontier for subsonic performance at this level. The previous needs of the 8.6 BLK, based on the 6.5 Creedmoor case, were short-action bolt guns or AR-10–compatible frame sizes. Also, because the 338 ARC produces usable velocities even in shorter barrels, shooters have SBR options for compact hunting and shooting pleasure. 

The 338 ARC is not designed to be a paper-punching princess. It is intended to impact with authority on both targets and game. As far as game, it’s ideal for medium-sized critters on down. Black bears, deer, antelope, and hogs are all viable options for this chambering. Essentially, anything you’d take with a 44 Magnum is 338 ARC-compatible.

There are two current cartridge options. While the focus of the 338 ARC was subsonic performance, Hornady also introduced the aforementioned 175-grain HP. The 175-grain bullet is marketed with a 200-yard zero and is 4.2 inches high at 100 yards. It has an advertised muzzle velocity of 2,075 fps. The SAAMI-spec’d barrel length was 16 inches. This bullet configuration has the same platform compatibility as the 307 Sub-X — micro action or AR-15.

The 307 Sub-X is marketed with a 100-yard zero with 33.9 inches of drop at 200 yards. The bullet itself is designed to expand down to 900 fps. It has an advertised muzzle velocity of 1,050 fps. As discussed, this doesn’t vary significantly with different barrel lengths. 

SANS SOUND AND FURY

Playing in the subsonic realm means less noise. With the widespread use of suppressors, an already quiet shooter experience becomes even more hearing-friendly. While quiet in an AR, the 338 ARC is nearly silent in a bolt gun.

An interesting side note on 338 ARC suppression: Due to pressures and velocity, some suppressors intended for pistol calibers are compatible with the 338 ARC, eliminating the need for traditional, expensive big-bore rifle cans. For example, numerous outstanding 9mm cans fit well with both the platform and the purpose of the 338 ARC. Be sure to check the pressure specs for your pistol suppressor before use. 

Besides being soft-spoken, the 338 ARC is soft-shooting as well. The compact Grendel case, when paired with the 307-grain Sub-X, produces an excellent cartridge for petite shooters, recoil-sensitive shooters, or those who don’t enjoy a snappy-shooting gun. This stays true even in the smaller rifles the round can be chambered in, such as micro-action bolt guns, AR-15s, rifles with standard barrel lengths of 16 to 18 inches, or SBRs.

BUILDING A 338 ARC RIFLE

When I first saw the 307 Sub-X bullet, I was intrigued. It is touted as “The Big Little Cartridge that packs a punch!” Being a 5-foot-tall 130-pound woman with a passion for firepower, I knew I needed one in my gun vault.

After extensive research and several conversations with Hornady about what I wanted to do, I elected to build a bolt gun with a more classic, almost safari-sporter feel. I briefly considered building an AR, but I decided a smallish bolt gun would better fit my objectives. The focus would be on shooting the 307-grain Sub-X, but I wanted to be able to fire heavy or light bullets at subsonic or supersonic velocities from the same platform.

For a barrel, I went with a 16-inch-long tube with a 1:8 twist, which is the SAAMI spec. It is carbon steel, with a barrel band and irons, and an option for a QD optic mount. The medium-contour model from BSF Barrels is threaded for a suppressor. For a sporter, I wanted classic irons from Skinner Sights as well as the capability for a clean, distance-appropriate Leupold optic for use under 300 yards.

Initially, the build was paired with a Silencer Central Banish 46 suppressor. At some point, I will explore the decibel and weight differences between appropriately sized pistol cans. The Banish 46, when paired with the 16-inch barrel and short action, yields a fun and functional finished product. The action is short, not micro. 

After conversations with Hornady, it would not create any issues with feeding or performance. I selected the Defiance Machine Rebel action with a three-position safety and a TriggerTech trigger. Because it wouldn’t be a dangerous-game gun, controlled-round feed was not imperative.

While my first choice was bottom metal, I decided to go with flush-mount AICS-compatible magazines. There are pros and cons to both choices, but it came down to a desire for simplicity and reliability in feeding.

The stock was a custom walnut piece tailored to my dimensions and constructed to accommodate the 16-inch barrel with aesthetically pleasing proportions.

The goal of the build was to put cutting-edge ballistics and modern components in a classic platform. The result would be a quiet, low-recoil, compact sporter-style rifle with energy enough to take medium-sized game out to 300 yards. It would be a fun-to-shoot, easy-to-carry option for my 10-year-old son and me as we pursue hogs, whitetails, predators, and black bears.

I just had to build it.

SOME ASSEMBLY REQUIRED

Once I received my action, trigger, and barrel, I carefully packaged everything up and shipped it to my gun builder, Tipton Burns of Texas Sporting Arms. Tip has built a few rifles for me over the last couple of years and always greets my various ideas with, “Hell yeah, let’s do it!” 

For this particular project, I supplied a stock from Rich Kaysa, owner of Kaysa Enterprises, made to my measurements and specifications, and Tip handled the headspacing, floating, and bedding. Then, I had Tip ship the bedded rifle to me so I could install an H-S magazine box. I got my rifle back and the H-S Precision package about a day apart. I looked at both and said, “Hell yeah, I can do that.” 

With the VP of the American Custom GunMaker’s Guild on the phone for guidance, and a file and a tube of lipstick instead of inletting compound, I did the final fitments on my 338 ARC. The H-S Precision mag box now fits beautifully in the stock.

For an optic, I mounted a 30mm Trijicon 1-4×24 AccuPoint with a green triangle post reticle in Warne rings. After a quick visual bore sight at the range, I was on paper at 50 yards on the first shot with the Hornady 307-grain Sub-X. The lateral impact was perfect, but the hole was 4 inches high at 50 yards.

Shooting the gun, the Hornady 307 Sub-X loads and the Banish 46 suppressor made only a pffft sound when the crisp trigger broke. The recoil was minimal and the noise irrelevant. The thwack into the backstop was more remarkable than the report of the rifle. Recoil on the 8.59-pound rifle, scoped and suppressed, was a push, really more of a gentle notification that a primer strike had occurred and a bullet was heading downrange. That definitely achieved the “fun” factor I had sought from the outset. 

Although my first impact was high, I kept the same point of aim and sent four additional rounds downrange to establish a 50-yard five-shot group of 1.64 inches.

The next step was 100 yards. With daylight fading and the temp dropping, I sent another five-shot group. Surprisingly, my point of impact was still high of the bull, but windage remained spot on. This five-shot group was 2.14 inches.

I elected to leave further adjustments until I had a chance to clean the rifle properly. Over the course of the 10 shots, the minimum muzzle velocity was 971.9 fps, and the max was 1,065.1 fps, yielding an average of 1,023.9. The extreme spread was 93.2 fps, and the standard deviation was 26.4 fps. 

The 338 ARC shooting experience was precisely what I had wanted.

The 338 ARC is just the latest ballistic innovation from Hornady. Perhaps all the characteristics the company put into it — low noise, low recoil, midrange power, and suitability for compact bolt and semiauto guns — may inspire other cartridge developers to try their hand at making something a lot of folks would like to shoot.

READ MORE ABOUT 338 ARC:

• Best Big Bore Quiet Thumper: Horandy’s New 338 ARC Vs. 300 BLACKOUT Vs. 8.6 BLACKOUT
• 338 ARC: Testing Hornady’s New Subsonic Thumper [BUILD]
• Hog Hunting 338 ARC: Safer, Better, And More Fun [BUILD]
• 338 ARC Bolt Action AR: It Gets Worse The Longer You Look At It [BUILD]

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