6.5mm Grendel

Development and history

The goal of the 6.5mm Grendel design was to create an effective STANAG magazine-length cartridge for the AR-15 platform that could reach 200 – and surpass the performance of the native 5.56mm NATO/.223 Remington cartridge. Constrained by the dimension of the STANAG magazines, the Grendel's designers decided to use a shorter, larger-diameter case for higher powder volume while allowing space for the long, streamlined, high ballistic coefficient 6.5mm (.264 cal.) bullets. Firing factory-loaded ammunition with bullets ranging from 90 to, its muzzle velocity varies from 2500 ft/s with 129- and 130 gr bullets to 2900 ft/s with 90 gr bullets (similar in velocity to a 77 gr 5.56 mm round). Depending on their case material and bullet weight, 6.5mm Grendel cartridges weigh 14.7 to.

The case head diameter of the Grendel is the same as that of the 5.6×39mm (.220 Russian), 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 magazine ammo capacities. A 6.5mm Grendel magazine with the same dimensions as a 30-round STANAG magazine will hold 26 rounds of Grendel ammunition.

Performance

Proponents assert that the Grendel is a good "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 (BC). For example, the 123 gr 6.5 mm Grendel bullet has more kinetic energy and better body armor penetration at 1000 m than the larger and heavier 147 gr bullet of the M80 7.62mm 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.

External ballistics

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 (50.8 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). Specific details are available as graphs derived from Alexander Arms' public domain load table linked below.

LE and Military usage

Serbia has adopted two rifles made by Zastava Arms in 6.5 mm Grendel caliber as main armament for its armed forces. The two rifles, designated Zastava M19 (officially adopted by the Serbian Armed Forces in 2022) and Zastava M20 (a compact carbine variant of the M19), are derivatives of the previous-issue M70 rifle. Serbia is also currently testing a light machine gun chambered in 6.5 Grendel based on their current Zastava M84 general purpose machine gun which is chambered in 7.62×54mmR. An American-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 of Užice, Serbia, will be tested for use with these rifles. The French police tactical unit GIGN announced in 2025 that they are partnering with Swiss ammunition maker SwissP Defenc to produce 6.5 Grendel cartridges for the GIGN.

References

Bibliography

• 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

References

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5. Outdoor Hub, [http://www.outdoorhub.com/stories/2015/10/13/photos-prototype-6-5-grendel-ak-rework-from-definitive-arms/ Prototype 6.5 Grendel AK Rifle from Definitive Arms], 13 October 2015
6. Gash, Steve. (2015-07-01). "Alexander Arms 6.5 Grendel Hunter Review". Gun Digest.
7. "Company History". Alexander Arms.
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9. ""Alexander Arms Announces: The 6.5 Grendel Is An Official SAAMI Cartridge "".
10. "6.5 Grendel is Approved as SAMMI Cartridge — Alexander Arms Gives up "6.5 Grendel" Trademark « Daily Bulletin".
11. Guthrie, J. (November 16, 2012). "6.5mm Grendel: The Round the Military Ought to Have". Shooting Times.
12. [http://www.quarryhs.co.uk/The%20Next%20Generation.htm The Case for a General-Purpose Rifle and Machine Gun Cartridge (GPC) by Anthony G Williams] {{webarchive. link. (2014-11-09)
13. Ehrhart, Thomas P. ''Increasing Small Arms Lethality in Afghanistan: Taking Back the Infantry Half Kilometer''. pg 37-38
14. [http://sadefensejournal.com/wp/?p=808&page=2 Infantry Weapons Conference Report] – SAdefensejournal.com, 9 January 2012
15. [https://www.strategypage.com/dls/articles/Another-7.62mm-Bullet-For-M-16s-1-8-2012.asp Another 7.62mm Bullet For M-16s] – Strategypage.com, 8 January 2012
16. [http://sadefensejournal.com/wp/?p=2148 The Army's Individual Carbine Competition: What's Next?] – SAdefensejournal.com, 24 October 2013
17. (22 November 2017). "FIRST Military 6.5 Grendel Rifle? – 6.5mm Zastava M17 AK DMR in Testing by Serbian Army -".
18. (25 September 2025). "TFB Exclusive: Zastava M19 and M20 - Serbia's New Assault Rifles".
19. (16 December 2025). "Zastava's New 6.5x39 LMG Prototype".
20. "Prvi Partizan Ammunition".
21. "Prvi Partizan Ammunition".
22. "Prvi Partizan Ammunition".
23. "Војска Србије".
24. "SwissP Defence and GIGN present the 6.5 Grendel at SOFINS 2025".
25. "SwissP Defence and GIGN present the 6.5 Grendel at SOFINS 2025".
26. [http://www.defensereview.com/ssk-65-mpc-best-assault-rifle-cartridge-for-21st-century-warfare/ The 6.5 MPC cartridge by SSK developed by J.D. Jones at SSK Industries. Article on DefenseReview.com]