While the AR-15 platform has become the most popular rifle in the United States, and offers a plethora of different cartridges to suit every shooter’s need, the AR-10/LR-308/AR-308 platform hasn’t seen quite the same level of interest. In part that’s due to the fact that there is no standardization when it comes to large-frame ARs, making buying or building rifles or parts an exercise in frustration, requiring copious amounts of research rather than the plug-and-play operation of the AR-15.
When it comes to cartridges, the AR-308 family is most commonly found in .308 Winchester/7.62x51mm NATO. The 6.5 Creedmoor has become vastly more popular in recent years, and barrels can be found for the 6mm Creedmoor, .243 Winchester, .260 Remington, and even the 7mm-08 Remington. But bigger-bore cartridges such as the .338 Federal and .358 Winchester are less often encountered.
Against that backdrop, you would think that a new big-bore AR-308 cartridge would not be very popular. But a recently developed cartridge, the .375 RAPTOR, could end up becoming the gold standard against which other big-bore AR-308 cartridges are measured.
The .375 RAPTOR, as the name suggests, fires .375-caliber bullets. In that caliber range, bullets are normally found with weights ranging from 235 grains to 350 grains, with specialty bullets available from 175 grains up to 400 grains. That offers a significant amount of versatility. The .375 RAPTOR case isn’t just a .308 Winchester case necked up to .375. The case is first shortened, necked up to .375, and then the shoulder is formed to 35 degrees rather than 20 degrees to ensure proper headspacing.
That allows the .375 RAPTOR to take advantage of all the .375”-diameter bullets available on the market. Ballistic performance, with maximum pressure of 62,000 psi, is impressive. In essence the .375 RAPTOR offers the performance of classic cartridges such as the 9.5x57mm Mannlicher-Schönauer or 9.3x57mm Mauser, but in a modern semiautomatic rifle.
The .375 RAPTOR was developed as a hunting cartridge by Arne Brennan, the originator of what eventually became the 6.5 Grendel. It pushes a 235-grain bullet at over 2,500 feet per second, and 270-grain bullets at over 2,300 feet per second, with that performance coming from 18” barrels. Muzzle energies from an 18” barrel can approach or exceed 3,500 foot-pounds, rivaling even the 9.3x62mm Mauser.
Longer barrels can improve velocity, but not by significant amounts, making the .375 RAPTOR ideal for compact packages. An AR-308 with an 18” barrel and collapsible stock can make for a compact and effective hunting platform, and one which could double as an effective self-defense cartridge. The .375 RAPTOR’s ballistically efficient .375” bullets retain energy at distance, offering significantly more energy at long ranges too than smaller bullets from the .308 Winchester.
As with most independently developed cartridges, the real difficulty is acquiring ammunition or reloading components. Some factory ammo is available from the handful of companies that offer .375 RAPTOR barrels and components, as are reloading components such as formed cases and bullets. Otherwise, owners of the .375 RAPTOR are on their own when it comes to forming cases and loading ammunition.
If the .375 RAPTOR gains traction within the shooting community, the performance it offers could make it a popular option for those looking to get extra power out of their AR-308 rifles. It would likely take adoption or offering from a large mainstream firearms producer in order for that to happen, or for a producer like Starline to start producing brass. In that sense, the .375 RAPTOR’s big brother the .45 RAPTOR has a leg up on it.
The .375 RAPTOR also requires magazines for the AR-308 platform to be modified by using a file to file down the magazine ribs to allow the wider .375” bullets to seat, something that will also have to be done by end users. But in the meantime, for those who are willing to put in the work to build up a supply of brass, bullets, magazines, and ammunition, the .375 RAPTOR could play a very effective role in their survival armory.