The 338 ARC (Advanced Rifle Cartridge) from Hornady is the beginning of a shift in thinking about subsonic ballistics. With its diminutive case and comparatively massive projectile, it looks both intriguing and amusing. Let’s look at what this “Big Little” cartridge brings to the table and how it alters the subsonic realm going forward.
The 338 ARC round was conceived prior to the other ARC offerings that beat it to market. The Department of Defense (DoD) approached Hornady in 2016 with a need for a cartridge with greater terminal effectiveness at longer ranges while traveling at subsonic speeds. Hornady had a functional bullet in testing when DoD decided to shelve the project and focus attention elsewhere. It would be a few years before it re-visited.
In the interim, the 6 mm ARC and 22 ARC cartridges made their way to ammo shelves near you as 338 ARC sat waiting for completion. In 2024, the 338 ARC made its long-awaited debut to the ammunition market.
A sidebar here on the ARC family from Hornady: The premise behind Hornady’s “ARC” moniker is to create a cartridge/projectile combination that functions reliably and with a high level of performance and accuracy across a large spectrum of firearm brands and price points. Whether shooting a $500 or a $5,000 rifle, the premise is that the ammunition will perform functionally, consistently and with an acceptable level of precision.
The 338 ARC round, while designed to level up the subsonic realm, is also available in a 175-grain hollow point travelling at supersonic velocities. This is an important point of note for when we discuss platform selection.
For now, let’s talk components on the subsonic offering, specifically the 307-grain Sub-X bullet. The 338 ARC cartridge is based on a 6.5 Grendel case, which is then necked up to accommodate a .338-diameter projectile. The 307-grain Sub-X round looks like there is just as much bullet as case. Upon de-constructing a round, this observation was confirmed.
Ballistics are all about nuance, and subsonic ballistics can be especially complex. With supersonic rounds, in order to achieve greater terminal effectiveness down range, you can just hit the gas and add velocity. This doesn’t work with subsonic rounds because the whole point is to keep bullet travel below the speed of sound, approximately 1,125 fps).
With that in mind, Hornady created the 338 ARC cartridge. The petite Grendel case, when paired with the correct propellent, creates a perfect biome of powder burn efficiency, consistency and pressure to send the 307-grain Sub-X bullets downrange with authority.
Let’s (Not) Do The Twist
Powder burn is only part of the equation. Traditionally, subsonic rounds used a bit of a Tilt-a-Whirl approach to bullet travel. The 8.6 BLK round, for example, relies upon dizzyingly fast twist rates to accomplish terminal results down range. While effective when all the stars align, this doesn’t always happen.
Twist rates in that realm (1:3-inch, for example) can have quirks. First, bullet construction must be absolutely perfect. Flaws or manufacturing inconsistencies can lead to catastrophic bullet failure either in the gun or downrange. In the gun means barrel or suppressor damage. Downrange outcomes can be a missed or misplaced shot or poor bullet performance upon impact.
Second, bullet selection is typically limited to monolithic offerings—decreasing options and increasing shooting costs.
The extremely fast twist also limits ammunition options and applications for a given firearm. That one gun and barrel can only use that specific bullet-size range within those velocity parameters.
Hornady went at things differently with the 338 ARC cartridge, a chambering that would not only accurately and enjoyably shoot a 307-grain bullet at subsonic speeds, but it would propel a 175-grain projectile at supersonic speeds out of the same gun/barrel.
What does that look like? 338 ARC bullets are designed to be shot through barrels with a 1:8-inch twist. This allows for a lot more latitude in gun selection. Second, with subsonic ammunition, barrel length doesn’t follow the “length matters” edict found in supersonic rounds. A shorter barrel doesn’t equate to massive reductions in muzzle velocity. There is a 5 fps or less change in muzzle velocity per inch decrease in barrel length with subsonic rounds. Supersonic ammunition, in comparison, generally yields a 25 to 30 fps decrease per inch reduction in barrel length. This is dependent upon several variables but serves as a benchmark for comparison.
The Long And Short Of It
The 338 ARC round, based on the 6.5 Grendel case, is compatible with short-action bolt-action rifles. In an AR, it uses the AR-15 platform instead of the larger AR-10, which is used for the 8.6 BLK (6.5 Creedmoor case). This makes the 338 ARC especially handy for those seeking a compact rifle companion.
If you’ll recall, barrel length changes lead to negligible alterations in muzzle velocity in the subsonic realm. With that in mind, 338 ARC is a great candidate for carbines or SBRs.
One of the unique traits of 338 ARC is its compatibility with many pistol-caliber suppressors. There is no need to go out and get a can that will work for .338 Lapua Mag. to successfully suppress 338 ARC rounds. Many 9mm cans function with this caliber without the bulk and weight of larger options. As always, check your pressures, parameters and applicable regulations before using a suppressor.
So, what is 338 ARC good for? 338 ARC is a functional round for anything that you’d feel comfortable taking with a .44 Mag. From deer-sized critters on down to pigs and black bears, the 338 ARC is a fun and effective round at situationally appropriate distances.
The 338 ARC from Hornady is not only a fun-sized round that packs a wallop downrange, but also a new chapter in subsonic ballistic theory. It took the world of subsonic ammunition as we know it and leveled up the expectation for performance and accessibility. Hornady opened the world of subsonic enjoyment to a much broader spectrum of shooters and hunters. They took the one rifle, one bullet, one speed reality and transformed it with the introduction of the 338 ARC. Check out hornady.com for more information.
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