When you grab Faxon's first ever 338 ARC, the thought that comes to mind is, "How much did I pay for this?"
The rickety Faxon ION-X has poor tolerances, cheap stamping on the receiver, and a carbon fiber handguard that just looks tacky, kind of like that old lamp at your grandma's house. They also include a black and white manual printed off their HP printer, full of information not relevant to this particular gun. Before putting it on sale, Faxon priced their ION 338 ARC around $1,500. Not exactly cheap.
But actually holding the ION-X, you start to think how most airsoft replicas feel higher quality than this.
It Doesn't Work
Oh and by the way, it also doesn't work. When Faxon quietly released their first swing at 338 ARC in 2025, they proudly proclaimed that it was optimized to run Hornady's Sub-X load. The only problem is, it actually doesn't work with Hornady's Sub-X load, even using the magazine they shipped it with. The Sub-X jammed on the sixth round in the included 400 Legend Duramag. And using a 6.5 Grendel Duramag, the ION-X wouldn't even chamber a single round of Sub-X. Not one.
It also jammed with HSM subsonic in the 400 Legend magazine it shipped with. The HSM ran perfectly in the Diamondback DB-15 we recently tested, so the ammo isn't the issue here.
Finding the One Combo That Works
After extensive testing with different magazine and ammo combinations, we found exactly one formula that worked: the Duramag 400 Legend loaded with Frontier Subsonic 285gr. That combination ran 20 rounds at high speed with zero jams. Everything else was a disaster.
The Frontier subsonic also initially ran well in the 6.5 Grendel 26-round Duramag, cycling 20 rounds without issue. But then it started jamming, and eventually it wouldn't even load a round. So even the ammo that works in one mag doesn't necessarily keep working in another.
Why It Fails
A visual inspection of the feed ramps tells the story. The ramp geometry on the ION-X is clearly not optimized for the 338 ARC cartridge profile. The 338 bullet is a larger diameter than what standard AR-15 feed ramps are designed to handle, and rather than doing the careful machining work needed to accommodate that, Faxon appears to have just chambered a standard AR-15 upper in 338 ARC and called it a day.
This is a solvable problem. Diamondback proved that with their DB-15, which runs multiple subsonic loads flawlessly out of the box. Apparently Faxon just didn't try hard enough.
The 338 ARC Platform Problem
Granted, the 338 ARC platform itself does have some significant challenges. Since the bullet is too big for the magwell, it's physically impossible to make a polymer mag for 338 ARC. That's why Magpul and SureFire are making a new receiver design called ICAR with a 20% larger magwell that allows thicker polymer mags. The other 338 ARC problem is that the bullet is a much larger shape than AR-15 feed ramps are built for, which leads to jams.
But it's 100% possible to overcome those limitations, as Diamondback has proven with the DB-15. The platform challenges are real, but they're not an excuse for shipping a gun that doesn't run with the ammo you specifically say it's optimized for.
The One Good Thing: Weight
Faxon did do a great job of making an ultralight AR-15. The carbon fiber handguard, whatever you think of how it looks, does shed significant ounces. The ION-X is noticeably lighter than any other 338 ARC build we've handled. If you're prioritizing weight above all else, Faxon accomplished that mission.
But an ultralight AR that doesn't work is kind of like an ultralight paperweight.
Customer Service Response
We did reach out to Faxon customer service, and they recommended trying the CMMG 10-round magazine. It's not entirely clear why they didn't ship the ION-X with that magazine if it is a better option. The fact that their customer service team's first response is to suggest a different magazine than the one they ship the gun with is telling.
Bottom Line
We had really hoped Faxon's first 338 ARC would be the unicorn we'd been waiting for: light, functional, and accurate. Instead of a unicorn, it's more like an unhappy surprise hiding inside a rapidly deflating unicorn suit. At $1,500, the Faxon ION-X 338 ARC is impossible to recommend when the Diamondback DB-15 exists at a lower price point and actually works. If Faxon revisits the feed ramp geometry and ships it with a magazine that functions, there could be a great gun hiding in here. But that's not what they're selling right now.
Tested Magazine and Ammo Compatibility
- Magazines that work: Duramag 400 Legend (only with Frontier ammo)
- Magazines that don't work: Duramag 6.5 Grendel 26-round (can't chamber Sub-X at all, Frontier works briefly then jams), Duramag 400 Legend (jams with Sub-X and HSM)
- Ammo that works: Frontier Subsonic 338 ARC 285gr (only in 400 Legend Duramag)
- Ammo that doesn't work: Hornady Sub-X 338 ARC 307gr (jams in all tested magazines), HSM Subsonic 338 ARC 300gr HPBT (jams in 400 Legend Duramag)