Best Big Bore Quiet Thumber: Horandy’s New 338 ARC Vs. 300 BLACKOUT Vs. 8.6 BLACKOUT 

Hornady has come out with some bangers in their time like the 6.5 Creedmoor, 6.5/7/300 PRC, 6mm ARC, and more. Normally, these are long range cartridges, but Hornady has something sneaky up their sleeve — 338 ARC.

Maybe less revolutionary than some of their other offerings, 338 ARC is an interesting cartridge that has some awesome benefits… at least on paper.

WHAT IS 338 ARC?

Simply, 338 ARC is a brand new cartridge developed by Hornady to improve on the 300 BLK idea and bring the concept of suppressed subsonic hunting into a new era. While available in supersonic loads, 338 ARC really shines as a subsonic hunting cartridge. Bonus, it offers about 50% more power than comparable 300 BLK loads.

Using a Grendel Type II bolt, ARC magazines, and new 338 ARC brass, Horandy is launching a full line of supporting parts to deliver everything you need from cases to cauges to dies and seaters. Plus, factory ammo offerings using a 307gr subsonic and 175gr supersonic loads.

If you really want to boil it down: 338 ARC is more or less an improved 300 Blackout.

Disclaimer:

It’s important to note that much of this information is based on what Hornady has provided about 338 ARC on paper. 338 ARC isn’t available yet so we can’t test it ourselves. Once it is, we will and this will be updated. Until then, we’re working off Hornady’s homework.

BALLISTICS BASICS

For subsonic ammo, it’s fairly easy to compare the three cartridges since subsonic requires a max muzzle velocity of about 1,050 FPS. With a hard speed limit, it’s basically what bullet is heaviest will deliver the most energy. But raw energy isn’t the entire story as bullet design plays a huge part in what effect on the target it will have.

Bullets like the Hornady Sub-X are designed to expand even at lower speeds. How well this actually works is debatable from what we’ve seen, but if you get the ammo and range right it can be highly effective.

The same is basically true for 300 BLK since it uses common .30 caliber bullets with a normal twist rate.

8.6 BLK stands out because it doesn’t rely on linear velocity. Instead, the bullets designed for it tend to rely on the extreme twist rate and rotational velocity to aid in the expansion of the bullet once it hits meat. With a 1:3 twist, that is some insane RPM. The good news is that from the testing I’ve seen, it works. The bad news is that because of the insane RPM of the 1:3 twist, 8.6 BLK is extremely limited in bullet selection. 

Supersonic ammo is a bit more interesting to look at since the different cartridges produce very different results when you remove the speed limits. 

Horandy’s 338 ARC supers are loaded with 175gr HP Match bullets, 8.6 BLK for our example are Gorilla 190gr Supersonic Punisher bullets, and 300 BLK are 110gr Hornady Black X-MAX.

All three supersonic examples are fairly close in terms of bullet drop at 200 with only 6-inches, 8-inches, and 10-inches of drop for 300 BLK, 338 ARC, and 8.6 BLK in that order. 

Even at 300 yards, they stay friendly at 20-inches for 300 BLK, 28-inches for 338 ARC, and 34-inches for 8.6 BLK. Past that, the differences start to open up a lot. But really, 300 yards is likely as far as you want these bullets since these aren’t designed for long range. But if you want to go further, 110gr 300 BLK has the least drop past 300 yards. 

110gr 300 BLK drops 80-inches at 500 yards, 175gr 338 ARC drops “only” 118-inches, and the 190gr 8.6 BLK drops 139-inches at 500 yards.  

Those numbers will change depending on what exact ammo you feed each rifle. But these are some easy ballparks to think about.

WHAT IS BEST FOR YOU?

Again, we haven’t seen 338 ARC in action yet so this might be jumping the gun a bit. But assuming you don’t have any of these cartridges in your inventory yet and you’re looking to get into one of them soon, here is how it might play out.

300 Blackout

300 BLK is well-established and known for what it can and can’t do. Factory ammo is easy to find and there is tons of load data if you want to load your own. You can also use a standard .30 Cal suppressor for 300 BLK and be just fine for supers and subs. Getting into 300 BLK is fairly easy with just a barrel change for an AR-15, but most people do a whole new upper because it’s easier. Either way, being AR-15 based helps make it easy to get for most people.

300 BLK drawbacks are that of the three it has the least power. No matter how you slice it, you just can’t get as much from .30 cal as you can from .338 cal. Sub, super, doesn’t matter — 300 BLK will fall short. That doesn’t mean 300 BLK is weak, just that both 338 ARC and 8.6 BLK can hit harder.

Switching form super to sub ammo can make tuning your gas system a huge pain since it likely won’t work great with both. Huge drawback in my book is the fact that 300 BLK can chamber in 5.56 NATO rifles and cause kabooms. If you’re like me and you hate having 300 BLK in the house just on the off chance it somehow mistakenly gets in a 5.56 gun, this is a big deal.

338 ARC

338 ARC is also AR-15 based which again makes it easier to get into. But, 338 ARC requires a new barrel, new bolt (Grendel Type II), and new magazines. But, again, since most people are going to get a whole new upper anyway… not as big of a deal.

Having the backing of a huge ammo manufacturer like Hornady means ammo will probably be easier to find than 8.6 BLK. And because it uses a fairly standard 1:8 twist, you have a huge bullet selection to choose from when handloading. According to Hornady, 338 ARC will be gassed correctly with the same settings shooting both super and subsonic ammo.

That is something I’ll have to see to believe, but Hornady is making the claim and they don’t normally steer people wrong. 338 ARC is more powerful than 300 BLK, roughly 1.5x as powerful. My favorite upside, you can’t kaboom a normal 5.56 rifle by loading 338 ARC.

Downside, 338 ARC is brand new. Load data will be coming but it will come slowly and there is always the real possibility of quirks or bad information, just look at the story of .224 Valk as a warning. Because it requires new magazines, that is a pretty likely point of failure going forward until those get truly dialed in. 6 ARC has been around for several years now and still isn’t totally supported and 100% fool-proofed in the magazine department.

Also, kind of like 6 ARC, it’s reasonable to point at the bolt head design as not ideal. A 5.56 bolt head opened up to fit ARC cartridges doesn’t leave much meat to support the round. High pressure 6 ARC is known for breaking bolts and it’s not unreasonable to think that high pressure 338 ARC might do the same. However, since the goal of 338 ARC is normally going to be subsonic hunting or defense, pressure and bolt wear are less of a concern.

One last downside is that most people don’t have 338 cal suppressors. While some 9mm cans are rated for 300 BLK subs and those cans will likely work just fine for subsonic 338 ARC, they aren’t rated for it officially and could void your warranty at best. For people that don’t want to live dangerously, you’ll want to buy a dedicated 338 cal rifle can. Easier to do these days with short ATF wait times, but another step in the process.

8.6 Blackout

8.6 BLK is the hardest hitter of the batch. Still .338 cal bullets, but because it is AR-10 based it has more room in the magazine for heavier bullets and more room in the case for more powder when shooting supersonic. Both of these mean that for pure energy, 8.6 BLK is going to win. If you want to convert an AR-10 to 8.6 BLK, all you need is a new barrel since it uses .308 Win bolt and magazines.

In my book, that’s about where the benefits of 8.6 BLK end. Being AR-10 based means the rifles are more expensive, the uppers are more expensive, and even just changing the barrel is probably going to cost more than an AR-15 barrel in 300 BLK or 338 ARC.

Debatably, an 8.6 BLK rifle is going to be heavier also. Granted, you can get lightweight AR-10s or even small-frame AR-10s, but those are much more expensive and not an option everyone is going to pick. 8.6 BLK uses a cool idea for their bullets and the 1:3 twist, but that twist also limits you to a very small selection of bullets.

Almost anything that isn’t monolithic will be torn apart by the RPMs produced by the super-fast twist. Factory options for ammo are also very limited since no major manufacturer supports 8.6 BLK. The two largest brands making it are Gorilla Ammunition and Fort Scott Munitions.

While not nothing, those two brands are dwarfed by what Hornady alone could produce for the 338 ARC and what the dozens of manufacturers across the market produce for 300 BLK. And like 338 ARC, 8.6 BLK shares the problem of needing a .338 cal suppressor and most people don’t put having a .338 cal can super high on their list of must-haves.

LOOSE ROUNDS

What is right for you is a personal choice. But for me, 338 ARC is a very attractive option on paper. I don’t like 300 BLK for the simple reason that it can blow up a 5.56 rifle. Sure, the obvious answer is to not mix your ammo — but mistakes happen and I don’t like the risk even existing. I’ve seen what 300 BLK in a 5.56 rifle does in person, it ain’t pretty.

8.6 BLK was never high on my list of things to do because of being AR-10 based and having the… interesting 1:3 twist. I’ve shot 8.6 BLK rifles at CANCON and enjoy them, but it isn’t something I’m rushing out to build or buy.

While 338 ARC isn’t perfect, even on paper, it solves my kaboom issue and keeps it in an AR-15 package. Plus, more power than 300 BLK and more power is generally nice to have. Other than needing a new suppressor, I really like this idea.

More time will tell and we’ll be sure to bring you more content on 300 BLK, 338 ARC, and 8.6 BLK.