6.5mm Grendel showing variety of bullets—144 gr (9.3 g) to 90 gr (5.8 g)
|Place of origin||United States|
|Designer||Bill Alexander and Janne Pohjoispää|
|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)|
|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.
Development and history
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). Depending on their case material and bullet 6.5 Grendel cartridges 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.
In order to obtain ballistics that are superior to the 7.62×51mm cartridge, a weapon with a longer barrel and firing a heavier bullet is necessary. To achieve the same results from shorter length barrels, even heavier bullets are needed.
|Bullet velocity: 24 inch (609.6 mm) barrel|
|Bullet mass||Muzzle velocity||1,000 meter velocity|
As noted above, the Grendel case is very closely related to the .220 Russian case. In general, each additional grain of bullet weight will reduce muzzle velocity by 10.8 ft/s (61 m/s for each gram) and each additional inch of barrel length will increase muzzle velocity by 20 ft/s (2.4 m/s for each centimeter). Therefore, a handy rule of thumb is "one inch of barrel length equals two grains of bullet weight (1 mm → 5 mg)". Specific details are available as graphs derived from Alexander Arms' public domain load table linked below.
Army and police uses
Serbia is in process of adopting a rifle made by Zastava Arms  in 6.5 mm Grendel caliber as main armament for its armed forces. USA manufactured rifle in 6.5mm Grendel caliber may also be adopted in armament for special forces units after it passes testing in Technical Testing Center. Three types of 6.5mm Grendel ammunition produced by Prvi Partizan Uzice Serbia will be tested for use with these rifles. 
The 6.5 Grendel will probably never be adopted by the U.S. Military for two reasons; when compared to the 5.56 mm NATO round, the 6.5 Grendel is heavier and standard magazines cannot hold as many cartridges.
- .224 Valkyrie
- 6.8mm Remington SPC
- 6.5mm Creedmoor
- .30 Walker
- 6mm PPC
- 6mm AR: a 6.0mm version which shares Grendel's casing, but sends a (usually) lighter projectile up to 1,000 yards.
- .220 Russian
- List of AR platform calibers
- List of rifle cartridges
- Table of handgun and rifle cartridges
- "6.5mm Grendel (internet archive copy)". Alexander Arms. Archived from the original on January 9, 2012. Retrieved 2015-10-22.
- Guthrie, J (November 16, 2012). "6.5mm Grendel: The Round the Military Ought to Have". Shooting Times. Retrieved March 8, 2013.
- "Archived copy". Archived from the original on 2016-01-08. Retrieved 2016-01-04.CS1 maint: Archived copy as title (link)
- Lewis, Jack (2007). The Gun Digest Book of Assault Weapons. Gun Digest Books. p. 77. ISBN 978-0-89689-498-3.
- Outdoor Hub, Prototype 6.5 Grendel AK Rifle from Definitive Arms, 13 October 2015
- "Alexander Arms Announces: The 6.5 Grendel Is An Official SAAMI Cartridge "
- The Case for a General-Purpose Rifle and Machine Gun Cartridge (GPC) by Anthony G Williams Archived 2014-11-09 at the Wayback Machine
- Ehrhart, Thomas P. Increasing Small Arms Lethality in Afghanistan: Taking Back the Infantry Half Kilometer. pg 37-38
- Infantry Weapons Conference Report - SAdefensejournal.com, 9 January 2012
- Another 7.62mm Bullet For M-16s - Strategypage.com, 8 January 2012
- The Army’s Individual Carbine Competition: What’s Next? - SAdefensejournal.com, 24 October 2013
- Grendel: Not Quite the Monster They Think
- Guns 'n' Ammo: Book of the AR-15, 2004, "The 6.5mm Grendel", David Fortier, p. 66.
- Special Weapons for Military & Police, Annual #27 2004, "Beyond the 5.56mm NATO", Stan Crist, pp. 62–67.
- Guns 'n' Ammo: Book of the AR-15, 2005, "6.5mm Grendel and 6.8 SPC", David Fortier, pp. 32–44.
- Shooting Times, February 2005, "Cooking up Loads for the 6.5mm Grendel", David Fortier, pp. 52–56.
- Shooting Illustrated, September 2005, "6.5mm Grendel and Alexander Arms", J. Guthrie, pp. 34–37, 67–69.
- Petersen's: Rifle Shooter, March/April 2006, "Cartridge Efficiency—Why case shape matters", M. L. McPherson, pp. 22–24.
- Shooting Times, January 2007, "Other AR Chamberings", Sidebar Article, David Fortier, p. 56.
- Special Weapons, Semi-Annual #50 2007, "The Super Versatile AR", Charlie Cutshaw, pp. 44–45, 80–83.
- Special Weapons, Semi-Annual #50 2007, "5.56mm NATO Alternatives", Stan Crist, pp. 52–59.
- Shooting Times, March 2007, "Les Baer's 6.5mm Grendel AR Sets a New Standard", David Fortier, pp. 26–32.
- Special Weapons for Military & Police #52, Spring 2007, "BETTER-IDEA 6.5mm GRENDEL," Stan Crist
- Special Weapons for Military & Police #52, Spring 2007, "New Battlefield Requirements—New Rifles and Ammo Needed", Charlie Cutshaw
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