Imagine having a subsonic round with the same muzzle energy as a 44 Magnum but out of an AR platform and utilizing suppressors designed for 9mm. That is what the 338 Spectre delivers. Based on a 10mm Magnum Case (Not 10mm Auto) necked down to accept 338 caliber bullets, this is a potent and versatile cartridge for any AR or Bolt gun.
The 338 Spectre is a wildcat cartridge, with no SAAMI published specs, and at the time of this writing, nothing has been published on C.I.P’s website. Likely means this ammunition is not available in European markets. It is supported by Southern Ballistic Research (SBR) in Georgia but was originally conceived by Teppo Jusu.
History
It’s not hard to derive where the perceived need for this cartridge came from. The M-16/M4, and the AR-15 were introduced in the late 1950s with a new cartridge that was quite a bit smaller than the 7.62 calibers that had been in service in the military since the introduction of the 30-40 Krag in the 1890s, The new high velocity .22 (5.56mm) caliber projectile that was fielded during Vietnam war had it’s growing pains.
The high-velocity bullet has a few mechanisms of injury besides creating a .22 caliber hole. The high velocity combined with the long nose of the bullet was inherently unstable, and when the nose of the bullet was slowed suddenly the heavier base would kick around and begin to tumble. Bullets did not often track straight through a combatant but would tumble, and ricochet off bones. Part of this was made worse (or better?) by the 1in12 twist, which is just barely enough to stabilize the 55gn bullet. In addition, it would create a hydrostatic shock, this is best compared to shooting a milk jug full of water. When the bullet enters a fluid, that fluid is displaced, and the speed at which it is done creates a shock wave that compresses and stretches tissue.
That was the theory, but in practice, it was less than convincing and it did not take long for soldiers to complain that it was taking multiple hits to enemy combatants in order to incapacitate them Various improvements were made to the ammunition, including increasing the weight from 55gn to 62gn and adding a mild steel core to improve penetration through the brush. In addition to bullet weight changes, the rifling twist rate was changed from 1:12 to 1:10 and eventually 1:7.
However, despite the improvements criticism continues to be levied today on modern battlefields. Part of this is due to design changes to the M16 platform, with modern rifles having 14.5 or 10.0in barrels instead of the longer 20in barrels fielded in the 1960s. This combined with heavier bullets had the effect of a reduction of 200fps or more in velocity, which impacted the overall terminal performance.
All of this serves as a backdrop to finding a newer cartridge, one designed around the 21st-century battlefield, and utilizing a more modern understanding of ballistics. There have been numerous attempts to find a replacement cartridge for the 5.56x45mm NATO, to date none of them have made it past trials. However that is not to say that new cartridges have not been adopted by Special Operators, just nothing has been adopted broadly across all branches of the service.
The 300 Blackout, which is nearly an identical twin to the 300 Whisper was introduced in the late 2000s by Advanced Armament Corporation. Designed to have ballistics similar to that of 7.62x39mm but out of an AR-style rifle. Unlike the 300 Whisper, it was introduced and accepted as a SAAMI Cartridge in 2011 which allowed for the standardization of the round. Soon many AR manufacturers began to market and sell rifles chambered in this novel round.
This round was adopted and used by team members in the Spec Ops community, and while 300 Blackout produced muzzle energies similar to that of a 45 Auto when loaded with a 220gr subsonic load, what was supplied to the military was a supersonic 110gr TAC-TX load. It is rumored that this load is what killed Bin Laden.
The development of the 338 Spectre occurred around the same time as the 300 Blackout and likely was an attempt to solve the same problem the 300 Blackout was attempting to solve. Namely, to maximize the versatility of the AR platform, and develop a load that could have favorable terminal ballistics from the shorter barrel length. However, it is more or less suffering the same fate as the 300 Whisper as it has never been submitted for SAAMI adoption, and remains a proprietary cartridge supported by SBR.
Offering muzzle energies similar to that of magnum pistol cartridge’s but out of a Gas Operated AR-15 platform. The 338 Spectre cartridge is not completely novel as it is worth mentioning that despite 338 Spectre being a fairly recent introduction (Introduced 2009ish) the idea is not a new one. (A common theme among “new” cartridges) It has similar dimensions to the 338 Whisper, introduced in the early 1990s by SSK Industries. The 338 Spectre uses the 10mm Magnum case, or can also be formed from a 6.8 SPC case, whereas the 338 Whisper uses a 7mm BR Remington case.
SSK Industries later introduced a straight wall case based on the .221 Fireball that would accept 338 Cal bullets and label it the 338 Whisper II. SSK Industries was known for their “Whisper” series of cartridges which were all based on heavy, subsonic, high B.C. rifle bullets. The largest of these was the .500 Whisper which was a .416 Rigby case shortened and necked to accept as a .510 diameter bullet.
SBR advertises this cartridge primarily for close support for the military and LEO. As either designated marksmen rifle (DMR) or for a primary arm for a tactical team. In its subsonic and supersonic loading, it carries more energy than the 300 Blackout. With a 225gr load, the firearm can be made two inches shorter and exceed the energy delivered by a 62gr 5.56rd fired from a 14.2in a barrel by about 25%. and can be suppressed with a fairly inexpensive 9mm Caliber Suppressor.
Unlike the 300 Blackout the 338 Spectre requires the use of 6.8 SPC mags and bolt face. While these are simple changes to make in an AR, it is two more components that need to be replaced while the 300 Blackout typically just needs a different barrel. From a safety aspect, the 338 Spectre will not chamber or fire in a gun chamber for either 5.56x45mm or 300 Blackout. This means that you are less likely to suffer a catastrophic failure that occurs when a 300 Blackout is accidentally chambered in a 5.56×45 NATO rifle.
I was personally introduced to this cartridge in the summer of 2016 when I had the opportunity to tour the Southern Ballistic Research facility while at a training conference for SAAMI. I thought the cartridge looked interesting and was different from any other cartridge I was loading at the time. I did a bit of studying before ordering an AR barrel from SBR a few months later.
Technical Specs
SBR lists the service pressure of this cartridge to be 46,000psi. Since they are the company that supports the round, producing both loaded ammunition, and supplying barrels/AR Uppers, I treat their specifications as gospel. There is some confusion on this, with QuickLOAD listing 37,500psi, but we will address this later.
Because this is a proprietary cartridge, chamber, reamer, and cartridge drawings are not publically available. The information we do know I have published in the table below.
Load Development Challenges
As with the 300 Blackout, the challenge with loading for the 338 Spectre is the subsonic loads. The propellent needs to produce a high gas volume in order to cycle the action but cannot accelerate the round faster than 1,050fps. This means that only a relatively few powders are going to work well for subsonic loads, these are the same powders used in 300 Blackout, namely A1680, CFE BLK, and Blackout. There may be others that will perform ok, but I have not personally tried them.
When loading for subsonic you are limited by the velocity, which is a bit of a reversal as usually you are limited is pressure. Subsonic loads will nearly all be below 37,500psi indicated by QuickLOAD (QL). Supersonic loads, do not have the same challenges as subsonic loads and a handloader will find most of all the same powders that work well in 300 Blackout will work in 338 Spectre.
The biggest challenge this cartridge has to offer is finding a source of brass. While SBR currently sells 338 Spectre brass, they are the sole provider on the market. This brass is thicker-walled than just necked down 10mm Magnum and will handle the abuse that an AR can dish out. With that said, the price is reasonable at around $.34 to $.36 per piece. Given the fairly low pressure of the cartridge, the brass should have a reasonably long service life should it be properly cared for. Especially if it is relegated to loading subsonic loads.
If you are looking to form your own, I would caution against using 10mm, Magnum Brass. I have gone this route and I have found that the case body will tend to split. Sometimes this can happen on the first firing. The walls of the case are just too thin. You are better off looking to use 6.8 SPC rifle brass, which sports the same head diameter but may use either large rifle or small rifle primers. Be aware this brass may have a reduced case compacity when compared to SBR 338 Spectre Brass as 6.8 SPC brass is designed to function with a 55,000psi service pressure.
Forming 338 Spectre brass from 6.8SPC is not a simple one-step neck down as it with the 10mm Magnum. 6.8 SPC brass needs to be cut down, reformed and then the necks need to be reamed to get a neck wall thickness of below 0.012-.013in. It is a process, which is why most people would rather just buy the preformed cases direct from SBR.
Advantages of 338 Spectre
The 338 Spectre may have become a serious contender for a spot that is now firmly occupied by 300 Blackout had it been introduced a few years earlier, and had it been submitted to SAAMI. However, as it sits right now it is hard to see what advantages it may have over existing cartridges that are more mainstream. I believe it still has a spot in the gun safe if you would like to try something new.
The muzzle energy of a 225gr load is greater then that of a 44 Magnum and due to the streamlined bullet that energy is carried further.
As with the 300 Blackout the 338 Spectre utilizes the AR-15 platform, which makes it versatile by nature. It also makes for handy bolt action or single-shot rifle as you can develop the energy needed to take medium-sized game without a long barrel. Of course, you could always trim down a 24in 308 Win barrel to 16in but you will not make friends at the shooting range. All of the wasted energy turns into sound and muzzle flash.
That also is the advantage of the 338 Spectre for home defense. A rifle that is easy to handle moving around the home, but packs more of a punch than a pistol caliber carbine or 300 Blackout without the deafening muzzle blast associated with a shorter barrel 5.56x45mm.
Lastly, it also is a good caliber for cast bullets. Much like the 300 Blackout, Cast Bullets make for good subsonic range fodder. 1600fps is pushing the upper limits of what cast bullets will typically shoot well, but it does give you a rifle that can shoot subsonic rounds giving muzzle energy nearly twice that of the 45 ACP, or rounds that have as much muzzle energy as a 5.45x45mm does when shot from a 20in barrel.
Disadvantages
6.8 SPC magazines are not as common as 5.45x45mm mags, and they typically only hold 25 rounds for a mag that is the same size as a standard 30 round AR-15 mag. Since the case head of the 6.8 SPC is identical to that of the 338 Spectre, you can fit 25 rounds in without a problem.
Because this is a proprietary cartridge, you are limited to one source of supply for all of your reloading or shooting needs. Reloading dies are being offered by SBR, and are made by Lee Precision. Previously these dies were being made by CH/4D, (which I thought was the better company.) However, SBR is also offering a crimp die, which was not previously offered by CH/4D and I can get behind that.
I am always wary of a “single source” of anything, just because if that source kills the cartridge, everyone who bought into it may be up a creek. However, that is not unusual for wildcat cartridges/proprietary cartridges.
Other Information
I collaborated with a few other 338 Spectre shooters to help design a NOE300gr mold specific for the 338 Spectre. (NOE allows customers to submit their own designs provided they can get enough purchasers to justify running a batch.) The bullet does not have lube grooves and is designed to be either powder coated or epoxy coated. I would have preferred to have a couple of lube grooves, but I got overruled. If you are not set up to do either, then there are other options that are not quite as heavy but have lube grooves.
Currently, SBR does not list a 700 Barrel on their website, but they are good to work with and if you are interested one can be made. I personally think it would be an excellent bolt action cartridge that would be very handy in the field.
Lehigh Defense has some interesting bullets that I suspect have been developed for their recently announced 338-10mm Nanosonic cartridge. It is a 10mm Auto necked down to 338 Cal which can be loaded with 250 or 300-grain bullets. At this point, I do not have much more information on this. However, some of the bullets developed for this small cartridge could give some interesting results in the 338 Spectre.
Lehigh lists load data for the 338 Lehigh which is a wildcat cartridge based on the 7.62×39 (6.5 Grendal can also be used) necked up to accept a 338 cal bullet. I do not know much more information on this cartridge and Lehigh Defense does not seem to have a lot of info on it either. QuickLOAD does not have the 103gr Close Quarters Bullet in its database, however, it does have a 105gr bullet made by Impala which they call a Light Weight High Velocity (LWHV).
Full disclosure, I had never heard of Impala Bullets prior to searching in the QL database for light 338 Cal bullets. They are based out of New Zealand, and a quick search of their website seems to indicate this bullet is no longer in production. However, it is a brass bullet or appears likely to have been made out of brass. Even if it was, it would still be questionable if it would be legal to import in the US as it is made out of brass, and I am sure the ATF would deem it to be Armor Piercing. (It makes me wonder how Lehigh Defense gets away with it, but some things are best left untouched)
For the purpose of running this “What If” scenario this QL file will provide us a reasonable estimate as to what we can expect with the Lehigh Defense bullet out of a 338 Spectre. For this, I typically set the parameters (We topped pressure out at 35,000psi) and then run a propellent table, which provides me a listing of all the powders ranked in order of what powder provides the highest velocity for the given pressure. In this case Win, 296, and Lil’Gun topped the list with a predicted velocity of around 2400fps.
Lehigh Defense does publish the Ballistic Coefficient values for their rounds so we can plug those into our calculator to come up with a reasonable estimate of downrange performance.
One last bullet that is of some note and produced by Lehigh Defense it’s their 232gr Subsonic Brass Solid. It has an expansion window of between 1200 and 700fps. It’s a bit lighter than an SMK 300gr bullet but it’s also made out of brass so the bullet is going to be longer, take up more case capacity, and have a lower sectional density. However, if you are looking for a subsonic hunting round for your 338 Spectre, this may be the ticket.
And if you like me and are curious to see what the drop might be like…
All this to say there is enough out there in 338 cal bullets to keep someone trying out new combinations and loads for some time. Which makes for a fun cartridge despite its challenges. Also, if you have a moment and want to check out some interesting, but a bit expensive bullet designs, Lehigh Defense has some kinda neat stuff for those who might be curious. I’m particularly interested in their Flash Tip (A titanium tip creates a bright flash on impact visible up to one mile by the naked eye) and would like to do a bit of work with their Xtreme Cavitator.
Conclusions
I have a small place in my heart for cartridges that are just a bit different. For me, the 338 Spectre helps fill to partially fill that hole. The AR-15 I built to host the cartridge is what you would call a “Franken’ gun”, I pieced it together with used and discounted parts. Putting the money in where it was needed, like a decent two-stage trigger, and a quality BCG. The barrel was brand new from SBR. However, I put on standard A2 stock and used a beat-up Troy Alpha rail that I got on a deal.
I am not done playing with it, I have more loads I want to try and add to the Load Database, and I need to do some accuracy and terminal ballistics testing. However so far what I’ve done with it, has me hooked. It is never likely to make it into the mainstream, and who knows how long SBR will continue to support it.
Should they drop it, I would hope that they release the design specs into the wild to keep us who have invested a bit into it, armed with a bit of information if we’d like to get a reamer made. Yes, I could make a reasonable guess based on my knowledge of cartridge and chamber designs, but I don’t want to step on any toes or add to the confusion of having another design spec with conflicting information.
With that said you have an opportunity to toy around with one, I would recommend it. Or stick around, as I do more with it, I’ll likely update the article.
Revision: 12/18/2021, this article has been revised and updated with more current information included updating the service pressure from 37,500psi to 46,000 based on conversations with Southern Ballistic Research who maintains the rights, and provides official support for the cartridge.
Page was also updated to fix links, photos, and proofed to make sure information was up to date.