Why Subsonic .300 BLK has Better ‘Trajectory’ than 6.8 SPC

Last year I began a journey into the world of the .300 Blackout that I intend to continue here. In my last three articles ( I, II, III ) about the cartridge, I documented the theory of use, supersonic abilities, and weapons built to use this fantastic cartridge.

To summarize my prior work in a few sentences, the .300 Blackout has become a serious choice for today’s consumer in supersonic form. The cartridge is able to launch a 120-125gr projectile at speeds of up to 2400fps from a 16” barrel and can utilize specialty ammunition that can deliver match-like performance at ranges of 500 or more yards with velocities upwards of 2800fps. The .300 Blackout is a fully mature, modern cartridge that allows a full range of use with only a barrel change on a standard 5.56mm weapon system and a serious ballistic upgrade at close to medium range over existing 5.56mm options.

In these articles, I will be discussing the original ideas behind the cartridge and the nature of the .300 Blackout as a subsonic cartridge while looking at other modern rounds in the same playing field. I also put together a custom AR pistol to test both handloads and factory ammo and talk about the performance gaps between barrel lengths in this cartridge.

300 BLK Pistol used for testing handloads
300 BLK Pistol used for testing handloads

U.S.A.-(Ammoland.com)- Here we will discuss how the trajectory of the .300 Blackout is better than that of other, faster rounds. We are, of course, not talking about ballistic trajectory, but rather the upward sales and popularity curve and the resulting technological gains in terms of subsonic bullet design. As you all probably know by now, the .300 BLK has taken the shooting world by storm. It has successfully outpaced the sales and popularity of other cartridges in the AR-15 world, such as 6.8 SPC, 6.5 Grendel, and many others, and done so with shocking gusto.

The reason for this is that, unlike rounds like 6.8 SPC, it offers the shooter a cartridge they actually want that is easily compatible with existing weapon platforms and can use off-the-shelf ammunition components with little to no issue. The Achilles’ Heel of the 6.8 SPC, for example, was specialty parts, magazines, and a shortage of good bullet options. The cartridge experienced commercial failure and is rarely used by anyone today except a few diehards as a result of the perfect storm of the 2009-2016 suppressor boom.

Where the .300 BLK truly shines is in its almost elastic versatility. There were never any good subsonic loads available for 6.8 SPC or 6.5 Grendel that could match those in the .300 BLK due to the fact that the smaller bore diameters didn’t lend themselves to loads at subsonic velocities. Why would this matter? The answer to this is twofold. The .300 BLK’s popularity came at a time when the suppressor market was exploding. Any supersonic cartridge could be suppressed, but not every supersonic cartridge could be easily made into an effective subsonic one.

Where the .300 BLK truly shines is in its almost elastic versatility.
Where the .300 BLK truly shines is in its almost elastic versatility.

The .300 BLK was readily adaptable to heavy bullets like the 220ge SMK, which at the time were available off the shelf where no comparable bullet was ready for 6.8 SPC or 6.5 Grendel. In order for a subsonic cartridge to be effective, it must have a bullet that carries enough mass under the speed of sound to do serious damage. Although it was possible to use heavy .277 bullets for the .270 in a 6.8 SPC, they could never equal the weight, and thus effectiveness, of .30 caliber bullets at the same speed. Instead of an advantage, it would be a deliberate handicap and a dangerous one at that.

This is a critical point in respect to the 6.5-6.8 cartridges. Their development was at a time when the idea was to improve upon the 5.56mm cartridge at distance.

The realities of the modern battlefield combined with the intense interest of the American public is what pushed the .300 BLK, despite being ballistically inferior at long range, into the spotlight and drove the others into abject obsolescence. In what was likely a first, the American public, usually concerned with long-range accuracy, decided with their wallets that a short-range, suppressor-friendly round was to stay and, as a result, serious design challenges were addressed in terms of bullet design.

What irks people that I know, especially those with a visceral hatred of the .300 BLK, is that it has a hard time fitting in with how they see rifles. The .300 BLK is a cartridge that can happily cross many performance barriers with the use of a single type of shotgun powder. Indeed, the same powders I used for my supersonic loads are also used in my subsonic loads by simply reducing the charge. It is troublesome to many staunch supporters of legacy calibers that a tiny .30 that uses shotgun and pistol powder at handgun velocities counts as a rifle in the sense of the word.

In terms of what a .300 BLK looks like in a subsonic sense, we need to look not at rifle cartridges, but instead at pistol rounds. Side by side, a 220gr subsonic load in .300 BLK is more akin to a .45ACP than it is to the supersonic form of the same cartridge. A standard .45 ACP can launch a 230gr bullet at speeds of about 800-950fps from a 5” 1911 pistol. My testing with 225gr subsonic loads in .300 BLK revealed that I could launch them at speeds of 950fps from a 7.5” barrel, making the two close in terms of speed.

Side by side, a 220gr subsonic load in .300 BLK is more akin to a .45ACP than it is to the supersonic form of the same cartridge.
Side by side, a 220gr subsonic load in .300 BLK is more akin to a .45ACP than it is to the supersonic form of the same cartridge.

Looking at the cartridge as a subsonic offering only, we are immediately confronted with some problems that make it, at least at close range, less effective than a .45ACP. How could that be? The .45 benefits from more frontal area, a myriad of bullet designs, proven, belt-carry pistol-sized weapon designs, and over one hundred years and billions of man hours of use. The new advancements in .300 BLK bullet design, like Hornady’s just-released SUB-X 190gr load, share more with pistol rounds like .45ACP than that of rifles and for good reason, but more on that amazing new round later.

The main concern with subsonic loads is that they share a single trait: their limits. Why I treat the .300 BLK in subsonic form as a specialty pistol load is that it has all the same limitations as pistol cartridges in that available bullet mass restricts necessary bullet speed. Because we need to have a bullet moving under the speed of sound to make it subsonic, we need the bullet to perform to our desired result within that limit. Taking a full size AR rifle and making it have the effectiveness of a pistol seems ludicrous and rightfully so. This is where the design of bullets becomes so critical.

The market for ammo that functions in a rifle, while flying at pistol speed, is fairly new. There are many radical designs available today that address this issue. First is rounds like the SIG 220gr OTM, despite being extremely accurate and high-mass, offer no expansion and instead rely on said mass to be effective. Penetration ability of these bullets is evident, with most of my test bullets being able to go through almost anything besides hardened steel plate during testing. They are not, however, recommended for hunting.

The other means of effectiveness is expansion, which is a hard thing to rely upon at low velocities, but new advances have corrected that. I have tested lots and lots of subsonic ammo in a variety of mediums over the last few years and have discovered that, especially in a hunting scenario, that traditional is better. Old-school softpoints and straight-up hardcast lead in the 200-240gr range often outperform new alloy-only bullets, which tend to shatter while not expanding. I have noticed this problem for some time and wondered why nobody else did, but it turns out Hornady took notice.

Hornady’s SUB-X 190gr load boasts a traditional design similar to the bullets found in their Critical Duty and Critical Defense handgun ammo and bests FBI protocol in terms of penetration and weight retention. I tested this load on barriers and glass out to 100 yards and found that the results were equal at ranges inside 25 yards. Recovered bullets that went through glass and material displayed remarkable toughness and maintained 70-80% of their mass. This is an incredible ammunition and would easily cross over to hunting should it be called upon.

Hornady has, without a doubt, raised the bar for which subsonic .300 Blackout is judged.

A distinct advantage at distance when using .300 BLK instead of a traditional pistol cartridge is, despite nearly equal bullet weight, superior energy retention and accuracy. The things that make a .45ACP effective at close range kill it at distance. The aerodynamic rifle bullets maintain their speed far better than short, fat pistol bullets and thus carry greater energy over distance.

I was able to routinely put ten shots of Hornady 190gr SUB-X into 2” at 100 yards. The load generated 1006fps over my Oehler 35P chronograph from a 7.5” Faxon barrel. Testing SIG SAUER 220gr loads proved better in terms of accuracy at that distance with a velocity of 990fps. This meant that I was able to, at 100 yards, deliver eyeball accuracy with virtually no recoil and still have more power on target than a .45ACP point blank. Not bad, huh?

The fact that there is so much speed, and thus energy, retained by the .300 BLK at subsonic velocities make it, with practice, a lethal round at 200 yards, but there are limits to that.  Many hunters rely on energy as a measure of load performance, but it can be deceiving. The subsonic .300 BLK in almost any form has less than 500 foot-pounds of energy at the muzzle, which is again right in the ballpark of .45ACP.

The problem with this is that most hunters consider 1000 foot-pounds on target to be the minimum, something that even .45 ACP can’t match despite being a very popular hunting pistol cartridge. I don’t look at it in terms of foot-pounds these days. Why? I think that bullet technology has arrived to where effectiveness is a function of mechanics rather than retained energy, meaning that if we can have a bullet that, at 100 yards, can pass through 15” of gel, pine boards, and leather while expanding reliably at around 1000fps, we have gone beyond the guidelines into new territory.

The .300 Blackout is, in my educated opinion, destined to be a cartridge that will settle in as a commercial and defense mainstay, a regular modern classic.
The .300 Blackout is, in my educated opinion, destined to be a cartridge that will settle in as a commercial and defense mainstay, a regular modern classic.

The function is there, but the classic numbers don’t match. I think we will begin looking at the new generation of hunting bullets the way we have classified long range bullets in the G7 rather than G1 drag coefficients. We need a new criterion to match our new technology and I think that is on the horizon.

So what does all this mean for you, the discerning shooter?

In this article and my previous three, I have detailed what makes the .300 BLK more popular and effective than its competitors, talked about available options and ammunition choices, and about the limitations of the cartridge. What we have with the .300 Blackout is a true do-all cartridge for the modern consumer. You can, with some limits, have a weapon that can be easily suppressed, maintain effectiveness and accuracy in a barrel under 8”, load it with ammunition that runs anywhere from 800fps all the way up to 2800fps, and take full advantage of a plethora of available reloading options.

In my next article I will discuss the building of a .300 Blackout with a 7.5” barrel and the necessary things to consider when making handloads for subsonics out of such short barrels.

Special thanks to:

  • Hornady
  • Brownells
  • Faxon
  • V7 Weapon Systems
  • Maxim Defense
  • Magpul
  • Midwest Industries

About Josh Wayner:Josh Wayner

Josh Wayner has been writing in the gun industry for five years. He is an active competition shooter with 14 medals from Camp Perry. In addition to firearms-related work, Josh enjoys working with animals and researching conservation projects in his home state of Michigan.

  • 17 thoughts on “Why Subsonic .300 BLK has Better ‘Trajectory’ than 6.8 SPC

    1. I always get a good chuckle when I read articles like this one. The writer’s wonder load must be awful hot. I don’t know where the writer got his data. The 300 BLK isn’t even in the same class as the the 6.8 or 6.5 Grendel. I guess if you like lobbing bullets at game, then maybe it works. Not for me. I’ve seen too many hogs standing after being shot by a 300 BLK several times. That’s all I needed to see. I never had a hog run on me after being shot by my 6.8. The BLK works out to 100 yards. But past that distance, there’s better choices. Why bother with the BLK when a 6.8 or 6.5 is better for hunting close in too?

    2. Running a small corral of 300BLK builds from 8″ SBRs for suppressed subs to a 16″ build for supers. I trade off between my 6.5 Grendel and the 16″ 300BLK for hunting in the desert SW. I assemble my own so running any 300BLK makes it easy with no special parts other than the barrel (or an adjustable gas block for suppressed subs, but really only if you want to reduce gas).

      I like my 6.5Grendel builds, but I’ve never been particularly happy with any magazines I’ve used (AA, Elander, CPD, ASC), though the Elanders have worked the best for me. Not really a problem for hunting using capped mags though. No broken bolts thus far. Excellent for making little holes a long ways a way on paper (way past where I’d ethically try a shot hunting). I do, however, find myself reaching for my 300BLK much more often for varmint control and hunting with the 6,5 being used mostly for longer range target shooting.

    3. The cartridge is able to launch a 120-125gr projectile at speeds of up to 2400fps.
      Funny, that matches the AK round (7.62 x 39) perfectly. And that round doesn’t cost fifty cents or more a round.
      The 300 aac is fading rapidly, ask any gun dealer. The ammo cost is killing it. No one makes cheap ball ammo for it.

    4. I seriously doubt that the 6.8 SPC is “dead”. Contrary to this article there are numerous very good bullets available for the 6.8 SPC such as the 100 grain Nosler Accubond which my family has used to kill approximately 10 deer, all with one shot. The 300 BLK only has one advantage, and that is if you want to shoot suppressed subsonic loads. In all other respects, the 6.8 is a vastly superior cartridge with better ballistics and better killing power-just look at the charts. Not trying to disrespect the author as all of his points dealing with suppressed use are valid, just pointing out that this article is very limited in its field of view and any suggestion that the 300 BLK is superior overall to the 6.8 SPC or the 6.5 Grendel is misleading. Always enjoy these articles and keep up the good work.

    5. I have been able to load this cartridge with the 88 grain Inceptor bullet from Polycase, and all I can say is wow. It was designed for safe use with steel plates, but damn does it fly. Something new to add to the stable.

    6. An article well written, informative and useful!
      Now I am even more satisfied about my recent 300blk Sig Rattler purchase…..

      Looking forward to your article on short barrel performance.

    7. I guess I’m the dinosaur, and happy being one. I have a 6.8spc that I shoot out of a 16” barrel and absolutely love it. I also have a 300 Blkout pistol with an 8 3/4” barrel and also love that! I don’t shoot subsconic so that part doesn’t concern me and won’t unless/until they reclassify suppressors, which isn’t likely with the weasels we have in Congress today.

      I consider myself lucky to have chosen both calibers and enjoy them both.

    8. Josh- if you’re serious about exploring the 300blk, I’d suggest looking into Trom projectiles. They have done years of research and development in changing the geometrical aerodynamics at the base of the projectile. They’ve just released a supersonic cartridge that has unbelievable accuracy out to 900 yards. Yes, 300blk supers that are accurate out to those distances. I e been following them with great interest. There’s been one Youtuber, tiborasaurusrex who has interviewed the owner and done some limited shooting with their products. They are also currently working on hunting/self defense rounds in addition to subsonic offering. Trom Tech. And no, I have no affiliation with that company or anyone associated with it. Thx.

    9. Interesting read. I think the .300 BLK proves that the industry and its customers have been too focused on velocity and energy figures, and not enough on good design. Our ancestors of the black powder era did not seem to be badly handicapped using weapons that often did not exceed the performance of today’s hunting handguns, and large numbers of elephant and other dangerous game have been taken with handguns that don’t come anywhere near the energy levels of, say, a .416 Rigby. Not to mention the exploits of men like WDM “Karamoja” Bell. After looking at lots of cartridge data and anecdotal info on performance for a possible rifle project which originated from the question, “if you could take only one rifle with you while having absolutely no idea of what you might run into, what would it be?”, the thing that jumps out at me is that, given a round with adequate penetration to reach vital organs, it matters far more where it hits than how hard it hits. Shot placement really is everything. Assuming that Americans are getting over their magnum obsession, the .300 BLK may turn out to be this century’s .30-30. Josh, you’ve gotten me to thinking about rebarreling a lefty CZ 527…

    10. All agreed, but I would sure like to see J. D. Jones from Idaho get a little love since he is the one who really designed the 300BLK back in the 1980s or early 90s. He called it the .300 Whisper, and it is slightly different from the BLK in dimensions, but it’s the same 5.56 case necked for the same .308 projectiles.
      But, like Weatherby, Jones kept the Whisper proprietary, and never released it for SAAMI specs. AAC did, but changed the dimensions slightly to differentiate it from Jones’ Whisper. Not that AAC shouldn’t get the credit for making it a standardized round, But the original idea was Jones’ and I would like to see that acknowledged by somebody, somewhere down the line…

      1. Hodgdon Lil’Gun, 21.0 grains(C) under a 125 grain Nosler Ballistic Tip as listed in Hodgdon’s online data center. I just bought 100 of those bullets to test. That may become my new hunting load if the bullet performs as well as the 110 grain Barnes.

        1. This reply was supposed to be to “Donkin”‘s question. Hodgdon’s website lists a maximum load of 21.0 grains of Lil’Gun with a 125 grain Nosler Ballistic Tip at 2,402 fps! Lil’Gun has become my “Go To” .300 Blackout powder. I am now using Accurate 1680 for 7.62×39 only.

      2. I’m curious as to where the idea that AAC “stole (ok, borrowed)” this round from J.D. Jones came from? I have read more than one place where he worked with AAC’s engineers to develop the Blackout. ???

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