338 ARC Ammo

Overview of 338 ARC Ammo

338 ARC (Advanced Rifle Cartridge) is Hornady's big-bore AR-15 cartridge, built from the ground up for suppressed shooting. It fires .338-inch bullets from 170 to 307 grains and cycles reliably with both subsonic and supersonic loads. The 307gr Sub-X subsonic load is about 50% heavier than a typical subsonic 300 Blackout bullet, and Hornady rates it at 1.5 times the energy of 300 Blackout subsonic.

338 ARC shares its 0.441-inch case head with 6.5 Grendel and 6mm ARC, so a 338 ARC AR-15 needs a dedicated barrel, a Type II Grendel bolt, and Grendel or 400 Legend style magazines. It is not interchangeable with 5.56 NATO, 300 Blackout, or 6.5 Grendel. If you are shooting a standard AR-15, see our AR-15 ammo page.

338 ARC Brands We Carry

• Hornady 338 ARC Ammo: Sub-X 307gr subsonic for suppressed shooting, plus the Black line in 175gr HP Match, 170gr MonoFlex copper, and 215gr FTX for supersonic hunting and target work.
• Frontier 338 ARC Ammo: 285gr FMJ range ammo for affordable training and plinking.
• Ultramax 338 ARC Ammo: 300gr HPBT remanufactured ammo for budget subsonic practice.

Best 338 ARC Ammo for Specific Uses

Why Buy 338 ARC Ammo from BulkMunitions?

• In stock and ready to ship. We only list ammunition that is physically in our warehouse. No backorders.
• Next-business-day shipping from our Knoxville, TN warehouse on orders placed before our daily cutoff.
• Case pricing on a brand-new caliber. 338 ARC in 200-round cases costs less per round than 20-round retail boxes, which are still hard to find.
• We tithe 10% of profits to Christian-based, 2A-supporting organizations every quarter, and our customers vote on where it goes.

Frequently Asked Questions

Is 338 ARC better than 300 Blackout?

For suppressed subsonic shooting, 338 ARC hits harder. Its 307gr subsonic bullet is about 50% heavier than a typical 300 Blackout subsonic bullet, and Hornady rates it at 1.5 times the energy. 300 Blackout still has the advantage in ammo selection and cost, and it runs on a standard AR-15 bolt and magazines, while 338 ARC needs a Grendel-type bolt and its own magazines.

What do I need to convert an AR-15 to 338 ARC?

You can keep your lower receiver. A 338 ARC conversion needs a 338 ARC barrel or complete upper, a Type II Grendel bolt, and magazines that feed the wider case, such as 6.5 Grendel or 400 Legend magazines. Standard 5.56 bolts and magazines will not work.

Is 338 ARC good for deer and hog hunting?

Yes. 338 ARC was designed with bullets that expand at lower impact velocities, so both the supersonic Black loads and the Sub-X 307gr subsonic load are effective on deer and hogs at typical AR-15 hunting distances. Supersonic loads like the 215gr FTX shoot flatter for longer shots. Check your state's regulations before hunting.

More About 338 ARC Ammo

Hornady released 338 ARC commercially in late 2024 after nearly a decade of development that began at the request of a government customer. The goal was a cartridge that could outperform 300 Blackout in a short, suppressed AR-15, especially with subsonic ammunition, while still cycling reliably with supersonic loads.

The case traces back to the .220 Russian, a descendant of 7.62x39mm, and keeps the same 0.441-inch case head used by 6.5 Grendel and 6mm ARC. It is loaded to a SAAMI overall length of 2.260 inches and a maximum average pressure of 52,000 psi. Barrels use a 1:8 twist, which stabilizes everything from the 170gr MonoFlex up to the 307gr Sub-X. The subsonic load is designed to run around 1,050 fps, and the supersonic Black loads leave the muzzle at roughly twice that speed with about half the drop.

338 ARC works well in short barrels. Testing from 10.5-inch and 16-inch uppers shows the subsonic load giving up almost no velocity in the shorter barrel, which makes it a natural fit for compact, suppressed hunting and home defense rifles. Rifles and uppers are now available from CMMG, Odin Works, and other makers, and factory ammunition supply is growing as the cartridge catches on.