This write up began life as a comparison between 338 Spectre, 338 ARC and 8.6 Blackout. However, as I began to dig into the comparisons, it quickly became clear that we needed to spend more time on the 8.6 Blackout and that was in a class of cartridge on its own. While we can draw comparisons to both the 338 Spectre and the 338 ARC, the bold claims made about 8.6 Blackout and the supporting data really tell an interesting story on its own.
338 caliber is sometimes known as 33 or 8.6mm, has been a somewhat niche cartridge; it tends to find markets in medium to large game hunting. 338 Federal, 338-06, 338 Win Mag, 338 RUM and most recently the 33 Nosler are examples of this. When ELR started becoming popular the 338 Lapua Magnum was popular for about a second as it was more affordable than the 50 BMG. That moment passed and we saw the market moved on to 338 Norma, 33XC and 338 Edge. At this point I think most of the serious ELR guys have moved on to larger 375, 408 and 416 calibers.
Even when 338 cal was popular no one got as excited with new 338 cartridge as they do with, say a new 6mm chambering. This is probably why when 8.6 Blackout was introduced at the 2022 SHOTShow, its subsequent fanfare caught many people by surprise. A few years later the 338 ARC again has grabbed the attention of many, mainly thanks to the marketing powerhouse that is Hornady.
I have been watching the 8.6 Blackout ever since I was introduced to it at the 2022 SHOTShow. I was deep into getting my 338 Spectre figured out and this immediately caught my attention. However, it just was not in the budget for me to invest in a new rifle and so I have been watching on the sidelines. Ever since I started making jacketed bullets for my 338 Lapua, I have been on the lookout for more cartridges that I could use my Corbin Dies to make bullets for. Once you have made that investment, you try and stretch it as far as it can go.
A Quick Backstory
To understand the 8.6 Blackout, we must look at its little brother, the 300 Blackout. The concept of the 300 Blackout was not new, J. D. Jones at SSK Industries introduced the 300 Whisper in the 1990’s which is so close dimensionally that you might think they are interchangeable (they are not). The story of the 300 Blackout is more of the right idea at the right time marketed by the right people. I am a fan of the cartridge as it is versatile. You can shoot 220 cast bullets which have all the energy of a 45 ACP but in an AR platform, then you can switch to a 110 grain Barnes TTSX and have a potent whitetail cartridge, or something great for home defense.
In fact, the 300 Blackout was adopted by and used by SOCOM for several years. Barnes had the ammo contract during my tenure there. They were loaded with a special brown radiopaque tip which would show up on X-rays, to aid field hospitals and surgeons who had to treat the bad guys who survived. Due to its popularity, 300 Blackout was accepted as a SAAMI cartridge and remains a popular chamber for ARs, though I think it’s starting to wane.
The 8.6 Blackout was built on the same premise, by the same folks that brought us the 330 Blackout. Kevin Brittingham, once the founder of Advance Armament Corp (AAC) and then subsequently Q, decided to add a twist (literally) to the design. They took a 6.5 Creedmoor case, shortened it slightly, and necked it up to accept a 338 (8.6mm) bullet. Typically to stabilize a subsonic 300 grain bullet you need a twist rate of around 1:8 and if you want to go a little heavier, a twist rate of 6 is not unwarranted. However, Q decided to add a twist rate of 1in3 which was a bold design decision.
The marketing buzz centered on the ‘Blender Effect’; the idea that increased rotational speed enhances terminal performance. This was backed up by some very convincing Ballistic Gel Tests. It is built on a sound premise, the faster the twist the faster the bullet is going to spin, and just how fast is the spin?
It Spins How fast?
To give you an idea of how much rotational speed you got from going 1:8 twist which the 338 ARC specs to a 1:3 twist that the 8.6 Blackout boasts I put together a chart.
Rotational speed is determined by two things, the twist rate of the barrel, and the velocity of the bullet when it leaves that barrel. For subsonic the velocity is conveniently capped, typically manufacturers shoot for 1050fps to keep the round safely below the speed of sound, regardless of if it is shot at sea level or in the Rockies. Rotational speed is not linked to the bullet weight; it does not matter if it is 160 grain bullet or a 350-grain bullet. If it leaves the barrel a 1050fps from a 1:8 twist it will be spinning 94,500 RPM.
As we can see, the 1:3 twist produces nearly twice the RPM as a 1in6.5 barrel. Immediately the results look impressive. The number is so large in fact that I think most people would have a hard time comprehending how fast that is. To give you a little perspective your engine idles around 800 to 1200 rpm, and when you’re cruising down the highway around 2000-2500 feels comfortable. Prior to the 2014 rule changes, Formula 1 engines had rev limiters set around 20,000 rpm. Jet engines routinely turn around 30,000rpm.
In fact, the only thing we are around on a semi regular basis is that spin at rpms near or exceeding that of a bullet are used in your mouth. Dental drills can spin upwards around 250,000 or more. If anyone is familiar with a dental drill, you can listen to it and hear the RPM’s change drastically when the dentist puts minimal pressure on the drill. This is because while they spin at a high rate of speed, they have very little torque. It is, after all, just air the air pressure that drives the little drill motor.
A bullet has a similar property as a dental drill. It leaves the muzzle at a high rate of speed, but the amount of energy that is required to spin up the bullet actually very little, and it’s also pretty easy to calculate. The energy at play here is referred to as Rotational Kinetic Energy, which is a mouthful so we’ll call it rotational energy. We only need to know the mass of the bullet, the diameter and the rate of spin. To keep things simple, I compared the rotational energy for the 338 Spectre, 338 ARC and 8.6 Blackout, all using a 300 grain Sierra MatchKing. For comparison I also added the same 69gr 223 Remington load as we had before.
Again, the graph shows that there is a notable increase in the energy content of the 8.6 Blackout over its peers. It is also worth noting that the 223 Rem load came in far lower despite having both a higher muzzle velocity, and a higher spin speed. This belays the fact that a smaller bullet takes less energy to spin to higher RPMs.
Without context the 45.7ftlbs looks to be substantially different than the 338 Spectre, again it would seem that there is truth to the coined “Blender Effect”. The energy must be there to be transferred. However, these numbers also lack context, how much energy is 35ish foot pounds?
When we calculate energy muzzle, we only consider the linear energy, and we do not calculate the rotational energy. The chart below clearly demonstrates why the amount of energy it takes could be considered a rounding error. With the 8.6 Blackout even with its increase 1in3 twist the rotational energy of the bullet amounts to roughly 4% of the total muzzle energy.
To put it in a different way 35ftlbs is roughly 1/3 the muzzle energy of a 40gr 22LR with a muzzle velocity of 1200fps. Another way to look at this, the energy of a typical 9x19mm load is between 320 to 350 ftlbs, a 45 ACP (The Lords Caliber) develops somewhere between 380 and 400ftlbs. The difference between the 9×19 and the 45 ACP has been one of the most hotly debated topics until recently when the market opinion has decidedly moved towards the godless 9x19mm (Obvious progression towards the end times). The difference in energy delivered? 30 to 40 ftlbs.
Terminal Performance
Terminal ballistics is a difficult subject. To study it properly, something has to die. Yes we can shoot ballistics gel and take measurements and largely we can make statements such as, “The bullet dumped most of it’s energy in the first 12 inches of penetration as evident by the temporary and permanent wound cavity. Ultimately the bullet penetrated 18in, expanded 1.5 times it’s diameter and kept 95% of it’s original mass”. What is much harder is comparing two bullets of similar make and performance and say with any level of certainty that “Bullet A” will result in a more ethical kill, or a faster kill, then “Bullet B”.
That is what I think this is coming down to. On paper we can say that the 8.6 Blackout will carry more energy due to the imparted rotational energy, but it’s hard to translate that to a measurable terminal performance. There’s too many variables that ballistics’ gel does not simulate well. For example the varying density of tissues and bones. There could also be one more mechanic at play here. It seems like most premium 8.6 Blackout ammo is loaded with machined copper bullets in the 350-360 grain range.
One of the challenges of subsonic ammunition is getting reliable expansion. There typically is not enough energy to get a bullet to mushroom even with a soft lead core as the exposed meplat on a spire point bullet is relatively small (not an issue on more blunt pistol bullets). Getting copper to mushroom reliably and consistently can be even more of a challenge as it is not a mechanical function as it is with lead bullets, it is typically hydraulic pressure. I find it to be quite plausible that the high rate of spin may aid in the initial expansion of a copper bullet. However, I have not found anything to prove or disprove that so it may be just my own conjecture.
The Price of Speed
This additional energy does not come without a price. It severely limits the performance of the 8.6 Blackout when it comes to supersonic loads. A natural bullet selection for a supersonic load in 8.6 Blackout would be something in the 160 to 185 grain range. This would achieve a muzzle velocity of around 2400fps depending on the load and barrel length. At this muzzle velocity the bullet will be spinning at nearly 600,000rpm.
Traditional cup-and-core bullets are not designed to withstand these extreme spin rates. You begin to quickly run into issues with bullets coming apart midflight, sometimes the moment they leave the muzzle, other times a short distance from the muzzle. This would damage, if not destroy, a muzzle device like a brake or a suppressor. To avoid this, you are limited to loading solid copper bullets which are strong enough to withstand the centrifugal force. These bullets usually cost a premium.
There are other technical reasons why you may not want to spin the bullet quite that fast, but Marc has pointed out that I am not trying to rain on anyone’s parade here. He correctly pointed out that the intended effective range of the cartridge is something less than a mile, and no one is going to be running this in a machine gun where barrel life and wear could be a concern. Marc’s a good guy, he keeps it real.
To his point and to be fair the cartridge was designed for a very specific purpose. Maximize the energy of a subsonic load, and by adding the 1:3 you do that. To that end it performs as it is advertised, you increase the energy muzzle by allowing long for caliber bullets to stabilize. You could theoretically stabilize a bullet up to 2.7in long which could weigh over 400gr, if you could find someone who would make one for you.
Wrap up
At the end of the day the 8.6 Blackout is a neat concept and I still like it. For me, I think I would find it most useful if it was paired with a 1:5 or 1:6 twist barrel, you would mostly get very similar terminal performance but also make it more of a dual-use cartridge suited for both subsonic and supersonic loads. This would truly make it an AR-10 version of the 300 Blackout. It would still be able to stabilize the 350 to 360 grain bullets that some folks are offering (at a premium) but it would also be effective at sending conventional 160 or 185 grain bullets without risking damage to a suppressor
Developing a new cartridge comes with a lot of risk and is not a cheap endeavor. Think of all of the tooling and dies needed for mass production. You are into it well over $100k for your first production run, and that probably doesn’t include tooling for special 1:3 twist barrel. Q developed it and brought it to the market, and they have done a good job marketing it. Time will tell if it sticks around and has as much staying power as 300 Blackout has had.
That’s all I have on that,
Jay