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.
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.
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.
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.
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.