6.5 Grendel

6.5mm Grendel
6.5mm Grendel showing variety of bullets—144 gr (9.3 g) to 90 gr (5.8 g)
Type	Rifle
Place of origin	United States
Production history
Designer	Bill Alexander and Janne Pohjoispää
Designed	2003
Specifications
Parent case	.220 Russian
Case type	Rimless, bottleneck
Bullet diameter	6.71 mm (0.264 in)
Neck diameter	7.44 mm (0.293 in)
Shoulder diameter	10.87 mm (0.428 in)
Base diameter	11.15 mm (0.439 in)
Rim diameter	11.2 mm (0.44 in)
Rim thickness	1.5 mm (0.059 in)
Case length	38.7 mm (1.52 in)
Overall length	57.5 mm (2.26 in)
Case capacity	2.3 cm3 (35 gr H2O)
Rifling twist	1 in 8" or 1 in 9"
Primer type	Small rifle
Maximum pressure	52,000 psi (AR-15 bolt), 58,000 psi (case strength)
Ballistic performance
Bullet mass/type Velocity Energy 90 gr (6 g) Speer TNT 2,880 ft/s (880 m/s) 1,658 ft·lbf (2,248 J) 108 Scenar (moly) 2,790 ft/s (850 m/s) 1,866 ft·lbf (2,530 J) 120 gr (8 g) Norma FMJBT 2,700 ft/s (820 m/s) 1,942 ft·lbf (2,633 J) 123 gr (8 g) Sierra Matchking 2,650 ft/s (810 m/s) 1,917 ft·lbf (2,599 J) 130 gr (8 g) Norma 2,510 ft/s (770 m/s) 1,818 ft·lbf (2,465 J)
Test barrel length: 24 inches Source(s): Alexander Arms Pressure-safe Load Data

The 6.5mm Grendel (6.5×39mm) is an intermediate cartridge designed by Arne Brennan, Bill Alexander, and Janne Pohjoispää as a low recoil, high accuracy, 200–800 yard cartridge specifically for the AR-15. It is an improved variation of the 6.5mm PPC. Since its introduction, it has proven to be a versatile design and is now expanding out into other firearms including bolt-action rifles and the Kalashnikov system.

The name "6.5mm Grendel" was a trademark owned by Alexander Arms until it was legally released to allow the cartridge to become SAAMI standardized.

The 6.5mm Grendel design goal was to create an effective 200–800 yard AR-15 magazine-length cartridge for the AR-15 that surpassed the performance of the native 5.56mm NATO/.223 Remington cartridge. Constrained by the length of the 5.56×45mm NATO round, the Grendel designers decided to use a shorter, larger diameter case for higher powder volume while allowing space for long, streamlined, high ballistic coefficient (BC) bullets. Firing factory loaded ammunition loaded with bullets ranging from 90 to 129 grains (5.8–8.4 g), its muzzle velocity ranges from 2,500 ft/s (760 m/s) with 129- and 130-grain (8.4 g) bullets to 2,900 ft/s (880 m/s) with 90 gr (5.8 g) bullets (similar in velocity to a 5.56 mm 77-grain (5.0 g) round). 6.5 Grendel cartridges depending on their case material and bullet weigh 14.7 to 17.8 grams (227 to 275 gr).

The case head diameter of the Grendel is the same as that of the .220 Russian, the 7.62×39mm, and 6.5mm PPC cases. This diameter is larger than the 5.56×45mm NATO, thereby necessitating the use of a non-standard AR-15 bolt. The increased case diameter results in a small reduction in the capacity of standard size M16/AR-15 magazines. A Grendel magazine with the same dimensions as a STANAG 30-round 5.56 magazine will hold 26 rounds of 6.5mm ammunition.

Proponents assert that the Grendel is a middle ground between the 5.56×45mm NATO and the 7.62×51mm NATO. It retains greater terminal energy at extended ranges than either of these cartridges due to its higher ballistic coefficient. For example, the 123 gr (8.0 g) 6.5 Grendel has more energy and better armor penetration at 1,000 meters than the larger and heavier 147 gr (9.5 g) M80 7.62 NATO round.