Why the .375 Raptor Is the Best Short-Barrel Big-Bore Option

[aminulis]

Unleashing Big-Bore Power in a Compact Package​

In the world of modern sporting rifles, the trend toward shorter, more maneuverable platforms has brought a new set of challenges for cartridge designers. While a 16-inch or 18-inch barrel is a fantastic all-around length, the appeal of a compact 12.5-inch short-barreled rifle (SBR) or AR pistol is undeniable for close-quarters applications, vehicle use, or simply for ease of carry in dense brush. However, a traditional rifle cartridge like the .308 Winchester suffers significant performance degradation when chopped down to these lengths. Its slower-burning powders and large case capacity are ill-suited for a short barrel, resulting in a dramatic loss of velocity, excessive muzzle flash, and a concussive blast.

This is where the concept of a "big-bore" cartridge optimized for short barrels enters the picture. The market has seen a number of these niche calibers emerge, most notably the .450 Bushmaster, .458 SOCOM, and .50 Beowulf, all designed for the smaller AR-15 platform. But a new contender has quietly redefined the category, providing a level of performance and versatility that eclipses its rivals: the .375 Raptor. Developed by Arne Brennan, the 375 Raptor stands out as the best short-barrel big-bore option, not just for its impressive ballistics, but for its elegant design and unparalleled compatibility with the proven AR-10 platform.

The Raptor’s Design: The Genius of Simplicity​

At its core, the genius of the .375 Raptor lies in its simplicity. It is, quite literally, a .308 Winchester case that has been necked up to accept a .375-caliber bullet and then trimmed. This seemingly minor modification has monumental implications. By using the .308 Winchester as its parent case, the .375 Raptor inherits the two most important features for a modern sporting rifle cartridge: compatibility with the AR-10/LR-308 platform and a standard .308 bolt face.

This is a critical advantage over its competitors. The .450 Bushmaster and .458 SOCOM, for instance, are designed for the AR-15, which forces them to operate under the constraints of a smaller action and bolt. The .458 SOCOM requires a rebated rim and a custom bolt, while the .450 Bushmaster uses a straight-wall case and a unique bolt. In contrast, a shooter building a .375 Raptor rifle needs only to swap out the barrel on an existing AR-10 or start a new build with standard, readily available AR-10 components. The existing bolt, magazines, buffer system, and gas block are all compatible. This makes the .375 Raptor incredibly accessible and cost-effective for anyone already invested in the AR-10 ecosystem.

Ballistics: The Hammer of Thor in a Hand-Held Package​

The true testament to the .375 Raptor's superiority is its ballistic performance, especially when fired from a short barrel like the popular 12.5-inch length. While the .308 Winchester bleeds velocity when its barrel is cut short, the .375 Raptor is engineered to thrive. The larger bore diameter, relative to the case's powder capacity, allows for a more efficient and complete powder burn within a shorter barrel length. This minimizes the unburnt powder and excessive flash that plague many other calibers in this configuration.

Let’s look at the numbers. From a 12.5-inch barrel, a .375 Raptor can launch a 270-grain Speer bullet at over 2,100 feet per second (fps). To put that into perspective, a 180-grain .308 Winchester from a 12-inch barrel typically achieves only around 2,200 fps. The difference in terminal energy is staggering. The .375 Raptor’s heavier, wider bullet, with a much greater sectional density, carries a colossal amount of kinetic energy—often exceeding 2,600 ft-lbs at the muzzle. This translates to an immense transfer of power on target, making it a devastatingly effective choice for hunting medium to large game, from wild hogs and deer to elk and even African plains game.

Beyond its supersonic capabilities, the .375 Raptor is also a phenomenal performer with subsonic loads, particularly when paired with a suppressor. It can reliably launch a massive 400-grain projectile at velocities just below the speed of sound (around 1,050 fps). This heavy, slow-moving projectile, combined with a suppressor, provides a whisper-quiet yet incredibly powerful option for close-range hunting or pest control. The fact that the same platform can seamlessly switch between a high-energy supersonic round and a stealthy, hard-hitting subsonic load without a change in platform is a level of versatility that is simply unmatched.

Direct Comparison: Why It Wins Against the Competition​

The claim that the .375 Raptor is the "best" is not hyperbole; it is a conclusion born from a direct comparison with its peers.

• Versus the .458 SOCOM and .50 Beowulf: These are undoubtedly effective cartridges, but they are limited to the AR-15 platform. This means they are working within the constraints of a smaller bolt face and action, which can lead to reliability issues and limited magazine capacity with some configurations. The .375 Raptor, operating on the larger, more robust AR-10 platform, has a built-in advantage. Furthermore, the .375 Raptor's bottlenecked case and superior ballistic coefficient mean it flies flatter and retains energy better at longer ranges than the more "blunt" projectiles of the .458 SOCOM and .50 Beowulf.
• Versus the .450 Bushmaster: While the .450 Bushmaster is a popular straight-wall cartridge, its projectile options are generally lighter and have a lower ballistic coefficient than the .375 Raptor. This translates to a more rainbow-like trajectory and faster energy loss downrange. The .375 Raptor’s ability to stabilize heavy, high-BC bullets gives it a significant edge in effective range and penetration.
• Versus the .308 Winchester: For short-barrel applications, the comparison isn't even close. While the .308 is a superb all-around cartridge, its performance from a 12.5-inch barrel is a mere shadow of its potential. The .375 Raptor was born for this role, meticulously designed to perform where the .308 falls short. It delivers more energy on target from a compact package, with a recoil impulse that, while substantial, is often described as a manageable push rather than a sharp kick.

Reloading and Ammunition Availability​

It is important to acknowledge that the .375 Raptor is a niche cartridge. Factory ammunition, while available from boutique manufacturers, is not as common as mainstream calibers. However, this is largely a non-issue for the discerning shooter for whom the cartridge was designed. The .375 Raptor is a reloader's dream. Creating ammunition is as simple as running a .308 Winchester case through a single sizing die. The wide array of .375-caliber projectiles, thanks to a lineage that includes the venerated .375 H&H Magnum, means reloaders have an almost endless selection of bullet weights, designs, and ballistic profiles to experiment with for any application.

This freedom to tailor loads for specific needs—be it a light, fast hunting bullet or a heavy, suppressed round—is another reason the .375 Raptor is a cut above. It allows the end-user to unlock the full potential of the platform, a level of customization that is more difficult to achieve with other big-bore options.

Conclusion: The New King of the Short-Barrel Big Bores​

For the hunter seeking a compact, maneuverable rifle that can anchor even large game with a single shot, the .375 Raptor is an unparalleled choice. For the enthusiast building a versatile short-barreled rifle for both supersonic and subsonic use, its ability to run on a standard AR-10 platform is a game-changer. The .375 Raptor’s blend of explosive terminal performance, ergonomic efficiency in a short barrel, and seamless compatibility with the AR-10/LR-308 platform makes it the logical and superior choice. It is a modern, intelligently designed cartridge that has earned its place as the definitive leader in the short-barrel big-bore market.

 

[Old Man with Gun]

You left out the possibility that it is not.
It is a good idea and decent performance, I've considered one myself, but it is not the best at everything .
This reads like an advertisement from someone who created an account just to post it.

For subsonic you want minimal case capacity so cartridges that fit an AR-15 will probably be quieter, pistol cartridges definitely will be. For people who want to use is only for Subsonic, a lever action in 44 Mag, 45 LC, 45-70, etc. Is a better choice.

Straight wall cartridges can be used in some states for hunting where bottle neck cannot. For some hunters, that alone is a disqualifier.

.375 bullets are expensive and not designed to expand at subsonic unless you get expensive specialty bullets while some other cartridges use thin jacketed pistol bullets that are cheap and already able to expand well. Even the bullets that are intended to be supersonic are mostly for dangerous game and would over penetrate most game, so questionable for North America.

The Raptor is really a reloaders cartridge at this point with almost no factory ammo.

Where the 375 Raptor is great is as a supersonic SBR AR-10 cannon. It does offer more energy than a 458 SOCOM and larger magazine capacity as well. But any tactical scenarios should take recoil and follow up shots into account.

As for factory firearms it is a custom build vs. available mass produced from numerous makers at a variety of price points.

Not trying to pick on you, but with an account that was just created, this looks like a business advertisement from someone posting as an individual.

 

[lash]

How is that a survey? Are you trying to be the head cheerleader in an all gay squad?

 

[45-90]

Wow!....that's a bit overwhelming description of the 375 Raptor. An AI sales pitch if I every heard one.

Why don't ya ask a guy who shoots one, if ya really want to know.

It is a pretty good caliber for an AR 10.
For short range super knock down power, okay with subs in the 350 gr SMK.
Mine has a 20" barrel so it can reach 2550 fps with a 235 gr Speer and 3400 ft/bs of muzzle energy...but that's only good on big game for about 200 yds. Because of poor BC of the bullet...but it's very accurate.

I scrapped the 3 twist 8.6 blkout unworkable...changed it to 6.5 twist and it works pretty well now in a bolt gun.

But the AR in 8.6 turned into a 375 Raptor AR. Definitely better than a 3 twist 8.6 but that is just about everything.

My AR 10 is modified to feed 2.940" cartridges.
Also note hybrid cases...not needed, but I have them.

The 350 gr SMK supers have a different COAL 2.940" than the subs at 2.8" to take up powder space, as this cartridge has
Too much capacity to be excellent at subs but it does a relatively good job, supers is where it's at for short range killing power on game animals, like smacking down hogs.

I like the 375 Raptor, it's fun to shoot, and have posted load data for it.
No hype just actual performance data, to see if the 375 Raptor might be a cartridge that fills a need for your shooting/ hunting endeavors.

 

[carbonbased]

My vote:

Gayer than Gay Tiger in a Gay Dance Club during Taco Gay Tuesdays

In other news

 

[lash]

Wow!....that's a bit overwhelming description of the 375 Raptor. An AI sales pitch if I every heard one.

Why don't ya ask a guy who shoots one, if ya really want to know.

It is a pretty good caliber for an AR 10.
For short range super knock down power, okay with subs in the 350 gr SMK.
Mine has a 20" barrel so it can reach 2550 fps with a 235 gr Speer and 3400 ft/bs of muzzle energy...but that's only good on big game for about 200 yds. Because of poor BC of the bullet...but it's very accurate.

I scrapped the 3 twist 8.6 blkout unworkable...changed it to 6.5 twist and it works pretty well now in a bolt gun.

But the AR in 8.6 turned into a 375 Raptor AR. Definitely better than a 3 twist 8.6 but that is just about everything.

My AR 10 is modified to feed 2.940" cartridges.
Also note hybrid cases...not needed, but I have them.

The 350 gr SMK supers have a different COAL 2.940" than the subs at 2.8" to take up powder space, as this cartridge has
Too much capacity to be excellent at subs but it does a relatively good job, supers is where it's at for short range killing power on game animals, like smacking down hogs.

I like the 375 Raptor, it's fun to shoot, and have posted load data for it.
No hype just actual performance data, to see if the 375 Raptor might be a cartridge that fills a need for your shooting/ hunting endeavors.

Good post. Thanks.

 

[mercracing]

I enjoy mine. Easy to load for, fun to shoot. My only goal is accurate hunting subs, and the 400gr Makers do that well. I’ll hunt with it this year and next year will be a Whisper.

 

[tekmann2377]

The original post is a weird mix of trolling and promotional material.

The touted velocity of a 270 gr bullet of 2100 fps out of a 12.5 inch barrel is actually inferior for hunting. I doubt most of the 270 gr projectiles generate profound expansion or hydrostatic shock at impact velocities of 2000 fps or less, especially since these bullets are intended for cartridges like 375 magnums. Their BC isn't great either and this limits range.

 

[db2000]

Duck is this you?!?

 

[Old Man with Gun]

I enjoy mine. Easy to load for, fun to shoot. My only goal is accurate hunting subs, and the 400gr Makers do that well. I’ll hunt with it this year and next year will be a Whisper.

I have a 458 SOCOM and it did everything I wanted Subsonic with 500g Maker Buzz Saw bullets until I saw a video about a Swiss Anti-material weapon for sabotage that used a 41 Mag case, 409g bullet and huge can.



My 458 SOCOM is kinda loud as a semi-auto and it got me thinking about a bolt, single shot, lever gun, etc.

I took a hard look at the 375 Raptor then, but due to cost and wanting something very compact to fit the sabotage theme, I built this 44 Mag T/C Contender with folding stock. 16" barrel, 1:16" twist to handle heavies and Hybrid suppressor.

A lot of fun, I mostly load 240g subs and supers, but it will stabilize a 300g JHP or 330g cast bullet. I could have gone SBR, and maybe some day I will with a custom 41 Mag barrel that can stabilize 400-500g bullets.

 

[lash]

I have a 458 SOCOM and it did everything I wanted Subsonic with 500g Maker Buzz Saw bullets until I saw a video about a Swiss Anti-material weapon for sabotage that used a 41 Mag case, 409g bullet and huge can.



My 458 SOCOM is kinda loud as a semi-auto and it got me thinking about a bolt, single shot, lever gun, etc.

I took a hard look at the 375 Raptor then, but due to cost and wanting something very compact to fit the sabotage theme, I built this 44 Mag T/C Contender with folding stock. 16" barrel, 1:16" twist to handle heavies and Hybrid suppressor.

View attachment 8776518

A lot of fun, I mostly load 240g subs and supers, but it will stabilize a 300g JHP or 330g cast bullet. I could have gone SBR, and maybe some day I will with a custom 41 Mag barrel that can stabilize 400-500g bullets.

Nice!

 

[45-90]

The original post is a weird mix of trolling and promotional material.

The touted velocity of a 270 gr bullet of 2100 fps out of a 12.5 inch barrel is actually inferior for hunting. I doubt most of the 270 gr projectiles generate profound expansion or hydrostatic shock at impact velocities of 2000 fps or less, especially since these bullets are intended for cartridges like 375 magnums. Their BC isn't great either and this limits range.

I run the 270 gr Speer at 2275 fps in a 20" 375 Raptor AR 10... but you'd have to test its expansion velocity, so you know your range limits...some bullets are down to 1800 fps some up around 2000 fps.

Here you look for bullets designed for low velocities like the 375 Winchester leveraction bullets made by Hornady or Barnes.

 

[Scottjames]

It gives big-bore stopping power out of a short tube without turning the rifle into a shoulder-punisher.

Heavy .375 bullets retain nasty energy even from 10–14″ barrels, feed reliably in modern AR-style builds, and are easy to tune for suppressed or unsuppressed use.

Punch > recoil, compact chassis, and one-rifle versatility for brush, woods, or truck carry, that’s why seasoned shooters pick it.

 

[Old Man with Gun]

It gives big-bore stopping power out of a short tube without turning the rifle into a shoulder-punisher.

Heavy .375 bullets retain nasty energy even from 10–14″ barrels, feed reliably in modern AR-style builds, and are easy to tune for suppressed or unsuppressed use.

Punch > recoil, compact chassis, and one-rifle versatility for brush, woods, or truck carry, that’s why seasoned shooters pick it.

I noticed you joined today and this is your first post. This thread is getting a lot of attention from first time posters.

What you say is also true of all the big bore AR cartridges. And if your heart is set on .375, why not .375 SOCOM?

 

[tekmann2377]

It gives big-bore stopping power out of a short tube without turning the rifle into a shoulder-punisher.

Heavy .375 bullets retain nasty energy even from 10–14″ barrels, feed reliably in modern AR-style builds, and are easy to tune for suppressed or unsuppressed use.

Punch > recoil, compact chassis, and one-rifle versatility for brush, woods, or truck carry, that’s why seasoned shooters pick it.

Shill material here.

I am not saying 375 Raptor has no use but there is only so much horsepower in a certain size case to push big bullets so fast.

If there is anyone who would find the velocity potential for it, 45-90 would. Even if you can get 2275 out of a 270 gr, that is still with a 20 inch barrel, not a 12.5 inch. I cannot imagine a sturdy bullet designed for 375 magnum would provide optimal expansion at 1800 fps.

Other cartridges that aren't so high velocity like 300 BLK get around this with bullets like the 110 TACTX that are custom designed to work in the 2350-2400 fps range, which is still higher than this. Checking out of this thread now.

 

[45-90]

I use a 20" AR 10 cause it gives the 400 gr Maker 1718 fps ...and it mushrooms 3 times the dia down to 650 fps...according to Maker....so one could still expect expansion way out past 1000 yds at this speed....if you could hit the vital area....which is doubtful.

The drop would be ridiculous at great distance...but if one chooses the right bullet ...and checkes it's performance at 650 fps in this instance.
One can potentially shoot at great distance.

There is loaded ammo with Maker bullets in 250 gr super and 400 gr subs at 1050 fps for those who don’t reload.

The 400 Maker is a bit lighter than 400 grs, I point mine in the lathe to 388 grs.

I ran all these different supersonic bullet weights at the same target with their varying velocities at 75 yds.

Supersonic is where the killing power is at but subs are fun to shoot.
Here are lathe turned bullets, modified for different performance options.

The 375 Raptor is a better all around option than the 458 SOCOM.
Brass for the 375 is free or close to it...easy to modify. Cheaper to shoot.
It's more accurate.
Match bullets with high BC available, for greater ranging capabilities with faster supers.
More energy and potential killing power with supers.
I have a 450 Bushmaster with a 16 twist and run resized .458" to. 452" 500 gr bullets in it, but its not as accurate or versatile as the 375 Raptor...but it's fun, I like it, and it will definitely kill most any large game up close.
Choices... but this is the real deal with the 375 Raptor...yep I tend to max cartridges out so there will be a bit less performance available in a 12" Raptor with supers.