Finding reliable 6mm Arc load data used to be a headache. Honestly, it still is if you aren't looking in the right places. When Hornady dropped this cartridge back in 2020, it wasn't just another "flavor of the month" release. It was a specific solution to a specific problem: how do we get 6DOF ballistic performance out of a standard AR-15 platform without blowing up the bolt?
The 6mm Advanced Rifle Cartridge (ARC) is basically a necked-down 6.5 Grendel. But don't let that simplicity fool you. Because it was designed for the Department of Defense, the pressure limits and the chamber specs are tighter than your average wildcat. If you're reloading for this, you've probably noticed that the data is split. You have the gas gun data and the bolt action data. Mixing those up is a recipe for a very bad Saturday at the range.
The Bolt Gun vs. Gas Gun Divide
Pressure is everything. In a standard AR-15, the 6mm Arc load data is capped at 52,000 psi. Why? Because the bolt face on an AR-15 is thin. When you hog out that much steel to fit the Grendel-style case head, you leave very little meat on the lugs. Pushing past that 52k mark in a gas gun is just asking for a sheared lug or a pierced primer.
Bolt guns are a different story.
If you’re running a CZ 527, a Howa Mini Action, or a custom build on a Remington 700 footprint, you can safely push to 62,000 psi. That 10,000 psi difference changes the entire personality of the cartridge. You're suddenly seeing velocities that rival the 6mm Creedmoor but with significantly less powder. It's efficient. It's soft-shooting. It's basically magic for PRS shooters who want to see their own hits through the scope.
Powder Choices That Actually Work
Forget the old standby powders for a second. While Varget is the "god-tier" powder for almost everything, it’s a bit too chunky for the small 6mm Arc case. You’ll run out of room before you hit the pressure nodes you want.
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Leverevolution is the secret sauce. Yeah, the powder originally made for lever-action 30-30 rounds. It’s dense. It’s spherical. It meters like water. Most importantly, it gives the highest velocities for the 103gr to 108gr bullets. If you're looking at 6mm Arc load data from Hornady’s 11th Edition, you’ll see Leverevolution consistently at the top of the speed charts.
CFE 223 is another solid contender. It’s dirty, sure, but it handles the heavy 108gr ELD-M projectiles incredibly well. Some guys swear by Hodgdon Varget or Vihtavuori N140, but you’re going to be dealing with highly compressed loads. You'll hear that crunching sound when you seat the bullet. It's nerve-wracking.
Bullet Selection and Twist Rates
You can't just toss any 6mm pill in here and expect it to work. The 6mm Arc was built around the heavy-for-caliber, high-BC (Ballistic Coefficient) bullets. We're talking 103gr, 105gr, and 108gr. To stabilize these, you need a 1:7 or 1:7.5 twist. If you bought a cheap barrel with a 1:9 twist, you're going to see "keyholing" where the bullet hits the paper sideways. It sucks.
- The 108gr ELD-Match: This is the gold standard. It’s what the cartridge was designed for.
- The 105gr Berger Hybrid: If you want precision and don't mind paying the "Berger tax," this is the most consistent bullet on the market.
- The 80gr Barnes TTSX: For the hunters. This turns the Arc into a legitimate deer and antelope dropped.
The 108gr ELD-M is usually loaded to an OAL (Overall Length) of 2.260 inches for AR magazines. But if you’re using those fancy windowless ASC mags or a bolt gun, you can seat them out longer to 2.290 or even 2.300 inches. This frees up case capacity. More room for powder equals more speed.
Why Case Preparation Matters
The 6mm Arc case is short and fat. It’s efficient, but it’s sensitive. Because the internal volume is so small (around 34 grains of water), even a 0.3-grain swing in powder can spike your pressures or open up your groups.
Starline brass is the workhorse here. It’s affordable and tough. Hornady brass is good, but the primer pockets tend to get loose after four or five firings if you're pushing the "bolt gun" limits. If you're a glutton for punishment and want the best, you can neck down Lapua 6.5 Grendel brass. It’s a chore. You have to turn the necks. You have to fire-form. But the consistency? Unmatched.
Real-World Performance Expectations
Let's get real about numbers.
From an 18-inch gas gun barrel, you should expect the 108gr ELD-M to hum along at about 2,550 to 2,600 feet per second. That doesn't sound fast compared to a .243 Winchester. But the .243 can't fit in an AR-15. The Arc stays supersonic past 1,000 yards. That’s the "why" behind this whole project.
In a 22-inch bolt gun? You can tickle 2,800 fps. At that speed, the wind drift is so minimal it feels like cheating.
I’ve seen shooters get frustrated because they see "YouTube influencers" hitting 2,900 fps. Nine times out of ten, those guys are trashing their brass or using 26-inch barrels that look like telephone poles. Stick to the published 6mm Arc load data from reputable sources like Hodgdon or Hornady. Don't be the guy who has to hammer his bolt open with a 2x4.
Temperature Sensitivity
Most of the best powders for this cartridge are "ball" powders. Ball powders like CFE 223 and Leverevolution are notoriously temperature sensitive. If you develop a "hot" load in the middle of a snowy January, and then take those same rounds out to a match in July when it's 95 degrees? You’re going to have pressure signs. Sticky extraction. Blown primers.
If you’re a serious hunter or competitor, consider looking at the Hodgdon "Extreme" line, specifically H4895. It’s a bit slower, and you won't get the top-end velocity, but it will hit the same spot whether it's freezing or sweltering.
Common Pitfalls for Reloaders
The biggest mistake? Using the wrong magazines.
The 6mm Arc is finicky in AR-15 mags. Standard 5.56 mags won't work. The internal ribs are in the wrong spot. You need dedicated 6.5 Grendel or 6mm Arc magazines. Even then, you might need to tweak the feed lips with a pair of pliers. It’s the "Grendel tax." You pay it in frustration until you get the timing right.
Also, watch your headspace. If you’re bumping the shoulder back too far during the resizing process, you’re creating excessive headspace. This leads to case head separation. You’ll know it happened when you pull the trigger, hear a "pop," and only the back half of the brass comes out of the chamber.
Strategic Next Steps for the Bench
Don't just go out and buy a pound of powder and start cranking the press. Start with a ladder test.
Load three rounds each starting at the "minimum" and working up in 0.3-grain increments. Look for the "flat spot" where the velocity stays the same even as you add more powder. That’s your accuracy node.
Invest in a decent chronograph. If you’re reloading without a Garmin Xero or a LabRadar, you’re just guessing. In the world of small-capacity, high-pressure rounds like this, guessing is dangerous.
Check your firing pin hole. Some AR-15 bolts have slightly oversized firing pin holes. This can cause "cratering" on the primer, which looks like a high-pressure sign even when your load is perfectly safe. Knowing the difference between a mechanical issue and a pressure issue is what separates the experts from the guys who just follow recipes.
Focus on consistent neck tension. The 6mm Arc responds heavily to how tight the bullet is held. A Redding Type-S bushing die is worth its weight in gold here. It allows you to control exactly how much you're squeezing that neck.
Verify your data across at least two sources. If the Hodgdon website says one thing and the Hornady book says another, split the difference and start low. The 6mm Arc is a phenomenal, efficient, and capable cartridge, but it demands respect at the reloading bench.
Get your brass sorted by weight. In a case this small, a 2-grain difference in brass weight can change the internal volume enough to ruin a long-range group. Separate your Hornady brass from your Starline. Keep your "match" brass in a separate box.
Finally, keep a detailed log. Note the temperature, the humidity, and how the recoil felt. The best 6mm Arc load data isn't what's printed in a book; it's the data you've proven in your own rifle, at your own range, with your own hands.