Can I build a 338 ARC on my existing AR-15 lower?

Yes. Your mil-spec lower, trigger, stock, and grip all carry over. You need a 338 ARC complete upper with a caliber-specific barrel and BCG. No new lower required.

Is 308 Win ammunition easier to find than 338 ARC?

Significantly. 308 Win is one of the most produced rifle cartridges in the world and sits on shelves at nearly every sporting goods store. 338 ARC is newer and primarily produced by Hornady. You can order it online without issue, but do not count on finding it locally on short notice.

What barrel length should I run for each cartridge?

A 16 inch barrel is the most common choice for 338 ARC builds. For 308 Win on an AR-10 platform, 18 to 20 inches is standard if precision work is your goal. Shorter 308 barrels cost you velocity fast.

How does 338 ARC compare to other big-bore AR-15 cartridges?

It produces more energy than 6.5 Grendel or 6mm ARC while staying on the lighter AR-15 platform. It also reaches farther than 450 Bushmaster or 458 SOCOM because its high-BC projectiles resist wind and drop at distance.

Calibers & Configurations

Which One Should You Choose, 338 ARC vs 308?

AR15 Uppers Editorial TeamAug 7, 2026 · 9 min read

Two black AR upper receivers with M-LOK handguards on a wooden workbench, each with a rifle cartridge standing upright in front of it.

338 ARC vs 308 Winchester compared: ballistics, platform size, recoil, and ammo cost. Find the right cartridge for your build. This guide breaks the topic down in plain language so you can make a confident decision for your build.

If you are hunting whitetail or hogs across open country, or stretching shots out on a lease, the question of 338 ARC vs 308 is a real one worth answering straight. Both cartridges hit hard. Both have a place in a serious build. But they are not the same tool, and choosing wrong costs you money and performance.

What Each Cartridge Is

338 ARC. Hornady introduced it in 2023, derived from the 6mm ARC case and necked up to accept a .338 caliber bullet. It runs in a standard AR-15 lower receiver, which is the detail that matters most if you already own one. Bullet weights typically run 185 to 250 grains. From a 16 inch barrel, expect roughly 2,350 fps with a 185 grain load and around 2,100 fps with a 250 grain load. A 1:9.375 twist barrel is the common spec to stabilize the heavier projectiles.

308 Winchester. Standardized alongside the 7.62x51 NATO round, in continuous service since 1952. It requires an AR-10 or LR-308 platform, which means a larger lower receiver, a longer action, and more overall weight. Precision loads typically run 150 to 175 grains, and a 168 grain bullet from a 20 inch barrel produces approximately 2,650 fps at the muzzle.

One point AR-10 builders should not overlook: 308 Winchester and 7.62x51 NATO are not identical. Commercial 308 Win is typically loaded to higher chamber pressure, and NATO chambers carry slightly more headspace clearance. A 308 Win chamber can safely fire 7.62x51, but firing max-pressure 308 in a loose NATO chamber is not ideal. Spec your chamber for the ammunition you plan to run. See the AR-15 vs AR-10 compatibility guide for the full platform breakdown.

Two rifle cartridges standing upright on a weathered wooden surface with a scoped rifle blurred in the background. — Similar case footprints, very different platform requirements.

Ballistics Head to Head

Open country can put you at 400 to 500 yards on a whitetail or hog without much effort. At that distance, retained energy and wind drift stop being range-day curiosities.

338 ARC vs 308 Winchester, approximate published figures

Cartridge	Bullet Weight	Muzzle Velocity	Muzzle Energy	500-yd Energy	500-yd Drop
338 ARC	185 gr	2,350 fps	2,265 ft-lbs	~1,200 ft-lbs	~45 in
308 Win	168 gr	2,650 fps	2,620 ft-lbs	~1,450 ft-lbs	~42 in

All figures are approximate and vary by barrel length, atmospheric conditions, and specific load.

The 308 hits harder at 500 yards, full stop. That said, the 338 ARC's heavier high-BC projectiles close the gap fast past 600 yards, and a 250 grain load with a G7 BC of 0.290 or better starts to outrun the 308 in wind resistance past 1,000 yards. If most of your shooting stays inside 500 yards, the 308 is the flatter, harder-hitting choice. Past that, the math shifts.

Platform Differences: AR-15 vs AR-10

A 338 ARC rifle with a 16 inch barrel typically weighs 7 to 8 pounds unloaded. An AR-10 in 308 Win with a 20 inch barrel comes in at 9 to 11 pounds. That is a real difference after three hours on foot. The AR-10 is also longer overall, which matters in a blind, in a truck cab, or any time you need to move fast between positions.

Parts availability is the other divide. AR-15 components are the most widely produced rifle parts in the country, so upgrading a 338 ARC build is straightforward. On the AR-10 side, DPMS-pattern and Armalite-pattern lowers are not always cross-compatible, which creates real headaches when sourcing parts or planning upgrades.

If you already own an AR-15 lower, a 338 ARC complete upper drops right onto it. That alone makes it the easier entry point for most shooters.

Recoil and Suppressor Compatibility

The 308 Win in an AR-10 generates roughly 18 to 22 ft-lbs of free recoil depending on load and rifle weight. The 338 ARC in an AR-15 sits closer to 15 to 18 ft-lbs with a 185 grain load. That gap surprises most shooters who assume a larger-diameter bullet means more kick. The AR-15 buffer system and the lighter projectile both work in the 338 ARC's favor.

Both cartridges use 5/8x24 muzzle threading on most builds, so suppressor mounting is straightforward either way. The difference shows up in the gas system. A suppressed 338 ARC on an AR-15 can run overgassed, and an adjustable gas block is usually the right fix. The AR-10 in 308 Win is a more mature suppressed platform with a wider range of tested components.

Hunting and Long-Range Use Cases

The 338 ARC handles deer and hogs cleanly out to 600 yards, and the 185 grain supersonic load carries enough terminal energy for elk-sized game inside 400 yards. The 250 grain subsonic load runs at approximately 1,050 fps, which makes it a practical suppressed hunting round where regulations allow. The compact platform is the other advantage: mobile hunters get a lighter, shorter rifle without giving up meaningful terminal performance.

Between 600 and 800 yards, the 308 Win with a 175 grain match load stays highly competitive and has decades of field-proven results behind it. It is also legal for hunting in all 50 states with no special restrictions. The 338 ARC easily meets minimum caliber requirements in most jurisdictions, but verify local rules before your season.

Ammunition Cost and Availability

This is where 308 Win wins clearly. Factory 308 loads from Federal, Hornady, Winchester, and Remington sit on shelves nearly everywhere, and match-grade 308 runs roughly $1.50 to $2.50 per round. If you realize you are short on ammo the day before a hunt, you can fix that locally.

338 ARC factory ammunition is produced primarily by Hornady, with very limited options from other manufacturers. Expect $3.00 to $5.00 per round, roughly double comparable 308 loads, and plan to order online. For a 338 ARC build to make long-term financial sense, reloading is worth considering seriously. Projectile options are solid from Hornady, Sierra, and Berger, though brass availability still lags well behind 308 Win.