AMMO COMPARISON 375 Raptor
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Arne Brennan, creator of 6.5 Grendel and other cartridges, designed 375 Raptor in a quest to do for 308 Winchester what 300 Blackout did for .223 Remington. Namely, neck it up to run larger, heavier bullets that deliver both supersonic and subsonic performance in a cartridge that’s efficient from a short barrel, suppresses well, and runs reliably in all the same platforms as its parent cartridge does.

By necking up and trimming 308 Winchester brass, the parent case is made ready to accept a .375 caliber projectile. Later this year, 375 Raptor headstamped, ready-to-load brass will be hitting the market from a source that will also be selling loaded ammunition.

A handful of .338 caliber cartridges such as 338 Federal, 8.6mm (.338) Blackout, 338 Whisper, etc. also succeed in firing larger, heavier projectiles than 308 Winchester within the same cartridge footprint, although they don’t increase the diameter or weight over .308 anywhere near as much as 300 BLK increased those measures over .223. Likewise, some .45 caliber cartridges like 45 Raptor were designed for AR-10 use, but projectile choice is an issue as it’s a very handgun-centric caliber, meaning ballistic coefficients are poor and these rifle-size rounds tend to push the projectiles at velocities beyond their performance envelope.

For the desired goal of plus-sizing 308 Win in a very similar fashion to 223 Rem/300 BLK and firing both supersonic and subsonic loads, Arne Brennan seems to have hit the nail on the head with 375 Raptor. It also benefits from the fact that it’s a caliber with a massive selection of fantastic, ideal rifle bullets already available.

Many dozens (if not hundreds) of great .375 projectiles are made all around the world, as 375 Raptor uses the same bullets as the venerable, 110-year-old 375 H&H Magnum and the newer 375 Ruger, among other well-established .375 cal cartridges. Due to the popularity of 375 H&H for big game hunting over the last century, most major bullet manufacturers have a long history of making and perfecting .375 bore projectiles. For the reloader, bullets start at about 28 cents each.

AMMO COMPARISON 375 Raptor ammunition
270 grain Speer SPBT after passing through 12 inches of wood

Most of the world’s best hunting bullets and many impressively high BC, long-range projectiles are available in the caliber. The only real exception is projectiles made for 375 Cheytac, which are too long to use in 375 Raptor (likewise, 338 Lapua Magnum projectiles are generally too long for the .338/8.6mm short action length cartridges).

Thanks to the larger bore diameter (there’s 48% more air volume per inch of barrel length in .375 vs .308) and the case’s small shoulder, 375 Raptor is extremely efficient out of a short barrel. Basically, it burns and uses its powder and gets the bullet up to speed uniquely fast.

For example, in particular from barrels between 10 and 18 inches in length, 375 Raptor will fire a 260 grain bullet at the same velocity that 308 Win will fire a 180 grain bullet despite using the same amount of gunpowder (case capacity is actually slightly lower) and the same maximum pressure.

Another benefit of the large bore volume and efficient powder burn is good results when shooting suppressed. With less unburned powder and lower gas pressures at the muzzle compared to, for instance, 308 Win (especially from shorter barrels), the 375 Raptor suppresses very well.

AMMO COMPARISON 375 Raptor ammunition
270 grain Speer SPBT

Supersonic loads:

Projectiles from 175 grains to 350 grains can be loaded to supersonic velocities. A fantastic, all-around hunting load capable of confidently taking any animal in North America is the 270 grain Speer Soft Point Boat Tail bullet, which is very affordable, shockingly accurate, and absolutely devastating on big animals. When loaded in 375 Raptor, velocity ranges from 2,100 FPS to 2,400 FPS depending on barrel length (10-inch to 20-inch). Raptor has been used to take everything from moose to Kodiak bears to Cape Buffalo and other African game.

AMMO COMPARISON 375 Raptor ammunition
400 grain Maker SCHP subsonic after passing the long way through a wild boar

Subsonic loads:

Projectiles from 350 to 450 grains are ideal for loading at subsonic velocities around 1,050 FPS. 400 grain subsonic expanding hollow points are available from a couple of respected projectile manufacturers, including Maker Bullets, and are available in loaded ammunition from a few companies. A 400 grain subsonic 375 Raptor still has more energy at 100 yards than 300 Blackout has at the muzzle! 350 grain Sierra MatchKing loads are amazingly accurate out to hundreds of yards.

Load examples:

235 grain : 2,400-2,675 fps : 3,005-3,734 ft-lbs
270 grain : 2,200-2,400 fps : 2,901-3,453 ft-lbs
400 grain : 1,061 fps : 1,000 ft-lbs

Ready to run in a bolt-action rifle or an AR-10 with nothing more than a barrel change — same bolts, magazines, gas systems, etc. as 308 Win — 375 Raptor shoots both high BC, supersonic hunting and target shooting loads as well as heavy, accurate subsonic loads for quiet hunting and plinking.

Rifling twist rates of 1:8 or faster are ideal for stabilizing the fastest, lightest supersonic loads all the way up to approximately 450 grain subsonic loads. Black Collar Arms (which, full disclosure, is a company I co-own) is the exclusive source for 1:6.25 twist 5R rifled barrels, a twist rate carefully chosen to be as fast as it can be without concerns over any existing high velocity projectiles shedding their jackets or hollow points spontaneously expanding due to being spun too fast.

Efficient powder burn in the .375 bore provides phenomenal performance from short barrels and great results when suppressed. After significant testing, both in the field and with chronographs and such, I recommend 12-inch barrels for pistol and SBR builds and 16-inch barrels for rifle builds. While you can (obviously) go longer, you’ll only gain about 12-15 FPS per inch of barrel beyond 16 inches and the juice just isn’t worth the squeeze. Go handy, go short.

It’s very simple and straightforward for rifle manufacturers to make 375 Raptor guns, whether bolt-action or semi-auto, and with so many ammunition manufacturers already making .375 caliber projectiles and 308 Winchester brass, turning those two things into loaded 375 R ammo is a walk in the park.

That said, though there are chamber reamers, reloading dies, loaded ammo (starts at around $1.70 per round), barrels, guns, and, soon, headstamped brass available for 375 Raptor, it is still a wildcat cartridge in that there is no official SAAMI standard for it. Hopefully this will change soon, as 375 Raptor is an amazing and extremely versatile cartridge with a heck of a lot going for it.

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37 COMMENTS

  1. At first blush, it sounds like this might be an excellent cartridge for accurately shooting the maximum possible range with a subsonic muzzle velocity.

    I am keenly interested in the maximum possible range with a subsonic muzzle velocity because such a platform would be stone-cold quiet. (While suppressors are effectively able to eliminate the muzzle report of supersonic loads, the supersonic crack of the bullet flying through the air is REALLY loud and would be audible for at least 200 yards if not considerably longer.)

    I don’t know what the practical range limitation would be since such a platform would have considerable bullet drop at long ranges. Imagine if this platform (shooting subsonic) could put accurate shots on target out to 400 yards and you are an enemy military squad on the receiving end: suddenly someone in your squad drops dead and you have absolutely no idea why, much less that a bullet killed your comrade and you have no idea where the bullet came from or even how far away the shooter was.

    • The 350 grain Sierra MatchKing 375 Raptor rounds loaded to 1,050 FPS are insanely quiet and will maintain or exceed 1 MOA accuracy out to [at least] 300 meters from a 10- or 12-inch barrel, which is as far as we’ve tested due to it meeting a specific requirement that involves your exact scenario.

      Compensating for the bullet drop is a non-issue. It’s dealing with windy conditions and the relatively long bullet flight times that make it a trickier shot than with a supersonic projectile arriving at target in less than half the time.

      • Jeremy S.,

        Thank you for the reply. I figure that 200 yards is more-or-less a no-brainer. I had no sense of whether or not a more practical limit would be something like 300 yards or 400 yards.

        And I agree that compensating for bullet drop is easy as long as you have an extremely accurate range-to-target at ranges up to 400 yards or so.

        I also agree that, past something like 250 yards, wind drift gets, shall we say “exciting”?

        I was/am really hoping that a subsonic platform can reliably reach out to 400 yards. An enemy squad (or even 100s of enemy soldiers) would have a very hard time fanning out across a circular area with a diameter of 1/2 mile and finding a sniper with excellent “woods” skills. And it would be all-but-impossible to find such a sniper in an urban environment.

    • I made some assumptions as far as BC (.6 G1 is what I gave it credit for), but it looks like the subsonic would have an approximate point blank range of 140 yards assuming an 8″ target size. That would give you around 200″ of drop at 400 yards, but still plenty of energy on target, over 700ft/lbs. Velocity is still 800 fps even at 1000 yards, but the drop gets ridiculous pretty fast.

      • Yeah it’s amazing how little the velocity drops when you’re firing a slippery BC bullet at subsonic speeds. But, yeah, with the long flight times the drop is aggressive haha

    • “…….(While suppressors are effectively able to eliminate the muzzle report of supersonic loads, the supersonic crack of the bullet flying through the air is REALLY loud and would be audible for at least 200 yards if not considerably longer.)……”

      Might be worth noting here.
      That supersonic crack is REALLY loud, but the overall sound is REALLY non-directional.

      I’ve shot suppressed supersonic 308Win and seen bystanders a few hundred yards away quickly turn their heads to look in the opposite direction from where the shot came from.

      • James Campbell,

        Oh, now there is an interesting idea. I can easily imagine that an unsuspecting person would unknowingly “follow” the sound of the bullet in the direction of its travel and conclude, erroneously, that it came from the opposite direction. Huh. I really want to find a way to test that.

        The closest experience that I have had was testing how loud a compound bow actually is in the woods when hunting. I stood 25 yards away from my cousin, within 5 yards of our archery target, and had him send an arrow. The sound signature of his bow 25 yards away was amazingly quiet–FAR quieter than I would have ever imagined. In fact the sound of the arrow (probably from its vanes) whizzing through the air as it got close was significantly louder than his bow.

        I mention that archery experience in support of your suggestion: the way something sounds at a distance can be significantly different than you imagine based on the sound next to the source.

        • Yeah it’s hard to hear the source direction in part because the bullet is traveling and the sonic boom is traveling with it, but off at angles like the V wake of a boat cruising across water, and it’s also echoing off any structures in the area. All that, combined with the fact that you don’t really hear the gunshot itself because of the silencer, make it quite hard to hear where a suppressed, supersonic rifle round is coming from. One shot. Fire a couple with people paying attention and listening and they’ll figure it out quick as they’ll be able to literally hear the bullet traveling through space and their brain will focus on the source quite efficiently.

        • 👍
          Spot on.
          Once people in the area ‘perk their ears up’ the source is readily defined.

  2. Big slow bullets, then small fast bullets, and back to big slow bullets. What’s old becomes new again. Still waiting for the plasma rifle.

    Philosophy aside, it looks interesting, and I hope your tweaks make it competitive with the other thumpers out there.

    • Velocity sells! Putting a super fast number on the box is just like designing fishing lures to catch the fisherman’s eye when it’s on the shelf rather than to catch the fish’s eye in the water haha. But I’ve always been a heavy-for-caliber guy with rare exception.

      Besides, 375 Raptor is shooting big bullets at the same velocity that 308 Win shoots smaller bullets. I did a lot of hunting with 185 grain 308 loads and now I’m running 270 grain 375 R loads and the velocities are within 50 FPS.

  3. Very interesting! I have lots of 375 bullets from my 375 Ruger bear hunting days.
    I have even more 358 bullets. Has anyone seriously looked into the 358 Win cartridge for AR 10 convesions?
    Maybe see similar benefits as a 375 .

  4. This is a solid, well-written article (that somewhat makes up for a few of Jeremy’s groan-inducing memes, lol).

    While I don’t own an AR-10 receiver that could utilize this .375R cartridge, I now know enough to make an educated decision to buy/pass, should I ever come across the opportunity. I do have plans to obtain or build one large-cartridge AR someday (likely only if I leave Kalifornistan for Free America).

    • A couple folks have done .50 cal short action / AR-10 rounds like Beck Ammunition’s .510 BECK, which I actually shot a long time ago. I don’t think any have really materialized though. Perhaps one issue is that the bullets are just so heavy for the amount of powder that it’s limited to a very short-range sort of an endeavor. The bullets are also really pricey. Maybe you could do a longer version of .50 Beowulf but then you’re back into the issue with a lot of the .45 cal cartridges, which is that you’re shooting pistol bullets at rifle velocities and the BC is crummy plus the bullets don’t perform well because it’s way faster than what they were designed for.

      .375 cal really seems to be a sweet spot where you can do heavy slugs up to 450 grains or so plus light stuff down to ~175 grains and they’re all proper rifle projectiles that do well at these velocities and they’re affordable and plentiful, and there’s everything from high BC target stuff to fancy hunting stuff to simple soft point hunting stuff to big game solids to subsonic expanding hollow points to etc etc etc

    • .500 Whisper is the answer to your question. 50 BMG bullets on a necked up 460 Weatherby Magnum cartridge case. Subsonic 750 grain bullets.

    • Kings can be un-throned. But our king is so absolutely full of it I wouldn’t recommend prying him off without protective gear on…

  5. I’d be interested in seeing a comparison with Kevin Brittingham’s 8.6 Blackout, which seems to be very similar in its concept and goals.

      • .458 SOCOM
        Same bullets as .45/70, not pistol bullets.
        AR-15 lower AND magazines.
        500 gr subsonic.
        350 gr JSP @ 1900 FPS.
        Not rimless though, rebated rim.

    • Here’s an image that compares the two across various ballistic specs: https://i0.wp.com/blackcollararms.com/wp-content/uploads/2022/10/375-vs-8.6.jpg

      8.6 BLK is cool and I like the idea. We’re chambering guns in it now at Black Collar: https://blackcollararms.com/product/pork-sword-stalker/

      I did briefly mention 8.6 BLK in this article in that short list of .338 cal (8.6mm = .338 cal) short action cartridges. To me, if we’re talking about doing for 308 what 300 BLK did for 223, I don’t really think going from .308 to .338 is enough of a bump. As you’ll see in that comparison image, even .375 still falls short of increasing the diameter by as much as 300 BLK (.308) did over .223, but I do think it was the correct choice given its great projectile availability and the slim pickings as soon as you go larger. Plus, any larger and you’d end up with a straight wall case. As-is, the 375 Raptor looks a hell of a lot like 300 BLK in terms of its shoulder size.

      • What company is supposed to be coming out with ready-to-go .375 Raptor brass? That’s the slow part of the reload is taking down the .308 brass.

        • I can’t say yet, as they want to make a splash with the announcement when they’re ready. Right now they’re wrapping up load development. They should be launching this at the end of the year or, maybe, at SHOT Show if they decide to hold off until then.

  6. @Rider/Shooter
    I designed a “45/70 Rimless” many years ago. Made brass from gettable new stuff, made dummy rounds and even had a SS 26” bbl made up. Rounds fed flawlessly through the unbarreled action, without projectiles (old .45 ACP auto reliability test).
    BBL company couldn’t thread for No. 4 Enfield so I shelved the project. Friend who fixes Brit bikes says he can cut threads on his lathe. It could give new life to rusty .303 Enfields and use modern brass and boolits.
    BBL’d action is soaking in WD40 now. Maybe I should give him a call.

  7. I’ve been running and reloading .375 Raptor from a custom AR-10 build and I love it. I have it in a 20″ barrel for supersonic loads, but looking to also build a pistol to shoot suppressed. I was tempted with the 8.6mm Blackout, but then I need to equip with yet another caliber…

  8. The 375 Raptor is a new cartridge by Savage Arms. It is a heavy-hitting, short action cartridge that was designed as a hunting cartridge. I prefer to get water blasting auckland and learn more new tips for gutter repair. Rather than making it as light as possible, Savage wanted to make sure that it could handle large game at close ranges.

    • Correction: “(2016) Arne Brennan, arguably the real “brains” behind the 6.5 Grendel cartridge, has announced the release of his latest caliber, the 375 RAPTOR. Building on the knowledge gained from the 45 RAPTOR (an improvement over .458 SOCOM), the 375 RAPTOR is, in-short, is a shortened and necked-up .308 Winchester for the larger diameter “slicker” 375 diameter bullets.” That said, you are correct that you can get .375 Raptor in a Savage barrel – but I don’t see it listed on Savage’s website as an option – only 375 Ruger. It’d be great if they did since maybe then one of the big ammo manufacturers would get it SAAMI qualified and I wouldn’t have to reload so much. (That said, the increased accuracy from doing handloads is really spoiling me…)

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