DuraMag 400 Legend 10-Round Magazine (338 ARC)

.338 ARC is Hornady's AR-15 cartridge built to run heavy subsonic and supersonic .338 projectiles on a standard AR-15 lower. The cartridge headspaces on a 6.5 Grendel Type 2 bolt face, but it does not feed best from 6.5 Grendel magazines. The fat, blunt-nosed .338 subsonic bullet feeds more reliably from the straighter internal geometry of a .400 Legend magazine, which is why Brownells points .338 ARC owners to this DuraMag rather than a Grendel mag.

The magazine is a 10-round unit with a 410 stainless steel body and DuraMag's orange AGF anti-tilt follower. The stainless body holds feed-lip geometry through long-term loaded storage better than polymer, which matters for a low-volume hunting and suppressed-shooting cartridge that spends most of its life loaded. DuraMag (C-Products Defense) makes the stamped-steel magazine that ships as factory equipment on a number of straight-wall AR-15 platforms.

For a .338 ARC build, buy two or three of these alongside the dedicated 6.5 Grendel/ARC bolt and a .338 ARC barrel. The cartridge is a precision and suppressed-shooting tool more than a high-volume blaster, so reliable feeding of the heavy subsonic loads outweighs squeezing extra rounds into a polymer body.