Jump to content

6.5mm Grendel

From Wikipedia, the free encyclopedia
This is an old revision of this page, as edited by Boris Barowski (talk | contribs) at 00:24, 29 September 2007 (, Replaced: × → x (2) using AWB). The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.
6.5 Grendel
6.5 mm Grendel showing variety of bullets 144gr to 90gr
TypeRifle
Place of originUnited States
Production history
DesignerBill Alexander
Designed2003 [1]
Specifications
Parent casePPC
Case typeRimless, bottleneck
Bullet diameter6.5 mm (0.26 in)
Neck diameter7.44 mm (0.293 in)
Shoulder diameter10.87 mm (0.428 in)
Base diameter11.15 mm (0.439 in)
Rim diameter11.2 mm (0.44 in)
Rim thickness1.5 mm (0.059 in)
Case length38.7 mm (1.52 in)
Overall length57.5 mm (2.26 in)
Rifling twist1 in 8" or 1 in 9"
Primer typeSmall rifle
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)
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)
108 gr (7 g) Scenar (moly) 2,790 ft/s (850 m/s) 1,866 ft⋅lbf (2,530 J)
Test barrel length: 24 inches
Source(s): Alexander Arms Pressure-safe Load Data
20" Grendel Counter-Sniper

The 6.5 mm Grendel (or 6.5 x 39 mm Grendel) is a 6.5 mm caliber intermediate cartridge developed in 2002 by Bill Alexander of Alexander Arms and Arne Brennan of Competition Shooting Sports. This cartridge is an evolution of Dr. Lou Palmisano's PPC case which has dominated competition shooting for over 20 years.[1] The 6.5 Grendel was designed as a low recoil, high accuracy, long-range cartridge for the AR-15 platform.

Development and history

7.62 mm NATO, 6.5 Grendel, 5.56 mm NATO

The Grendel design philosophy was "start slow and end fast". High muzzle velocities accelerate barrel wear and increase the percentage of recoil due to escaping gases but only yield good impact energy if the bullet is efficient at carrying its velocity downrange. Constrained by the length of the 5.56 mm NATO round, but wanting to launch a much heavier bullet, the Grendel designers hit on a short, fat case for more powder volume while saving space for long, streamlined, high ballistic coefficient (BC) bullets that give up little of their energy in-flight. Firing factory bullets from 90 grains (5.83 g) to 129 grains (8.35 g), its muzzle velocity ranges from 2,500 ft/s (760 m/s) with 129 and 130 gr bullets to 2,900 ft/s (880 m/s) with 90 gr bullets (similar in velocity to a 5.56 mm 77-grain round).

Timeline

  • 1998: Arne Brennan investigates .22 PPC, 6 PPC in search of a more capable competition and hunting round.
  • 2000: Arne Brennan begins shooting a 6.5 PPC wildcat cartridge from his custom AR-15 platform.
  • 2001: Arne Brennan and Bill Alexander introduced to each other by Lothar Walther.
  • Mar 2002: First production 6.5 Grendel brass cartridges manufactured to specification by Lapua.
  • May 2003: First prototype 6.5 Grendel weapon demonstrated at Blackwater Shoot-out.
  • May 2006: Independent ballistic gelatin testing completed for 90 gr. TNT, 120 gr. Norma, 120 gr. SMK, and 123 gr. SMK prototype.
  • Aug 2006: Bill Alexander publishes pressure safe load table for AR platforms with 14.5" to 28" barrels.
  • Feb 2007: Production Wolf brand ammunition becomes available.

Performance

Proponents assert that the Grendel is an ideal middle ground between the 5.56 mm NATO and the 7.62 mm NATO, taking the best attributes of each. It has a flatter trajectory and retains greater terminal energy at extended ranges than either of these cartridges due to its higher ballistic coefficient.[2] Production rifles have consistently achieved sub–minute of arc (MOA) groups at test ranges out past 600 meters.[3] On March 6, 2006, Arne Brennan achieved a witnessed 1.198" group at 660 yards.[4] Similar accuracy was demonstrated at recent Blackwater Shootouts.[5] Competitions have begun to be won with the 6.5 Grendel although use of the round is still not common in competition.[6][7][8]

External ballistics

Muzzle Velocity Change with Bullet Weight
Comparison of Assault Rifle Cartridges' Retained Energy

Muzzle velocity: 20 inch (508 mm) barrel

  • 108 gr (6.99 g) Lapua Scenar: 2,700 ft/s (820 m/s)
  • 123 gr (7.97 g) Lapua Scenar: 2,620 ft/s (793 m/s)
  • 144 gr (9.33 g) Lapua FMJBT: 2,450 ft/s (750 m/s)

1,000 meter velocity: 20 inch (508 mm) barrel

  • 108 gr (6.99 g) Lapua Scenar: 1,166 ft/s (355 m/s)
  • 123 gr (7.97 g) Lapua Scenar: 1,222 ft/s (372 m/s)
  • 144 gr (9.33 g) Lapua FMJBT: 1,213 ft/s (370 m/s)

As noted above, the Grendel case is very closely related to the PPC case. When sufficient load data was made available, a thorough study of the Grendel case, which constitutes a precisely dimensioned combustion chamber when the round is chambered, was done with the following results. In general, each additional grain of bullet weight will reduce muzzle velocity by 10 ft/s (3 m/s) and each additional inch of barrel length will increase muzzle velocity by 20 ft/s. Therefore, a handy rule of thumb is 1" of barrel length equals 2 grains of bullet weight. Specific details are available as graphs derived from Alexander Arms' public domain load table linked below.

Terminal ballistics

120 SMK test
123 SMK test
File:65g 120NFMJ T145 50 B.jpg
120 Norma test

Alexander Arms contracted Speer Law Enforcement to perform terminal ballistics tests in accordance with standard F.B.I. Protocols and their standard in-house procedures. They use 6" x 6" x 16" blocks of ten percent ballistic gelatin, calibrated with a BB. These results were made public in May of 2006. All tests were completed using either 14.5" or 16" chrome-lined Alexander Arms Tactical rifles and shot from either 50 or 100 yards to simulate combat conditions using short-barreled M4 format weapons. Barrel pressures were less than 240 kPa (50,000 psi). These are all production rifles and ammunition except for the prototype 123 gr Sierra MatchKing (now a production bullet). In addition to the photos shown below, a 90 gr TNT was tested resulting in explosive fragmentation after penetrating only 0.5 in (13 mm).

The 120 gr Sierra MatchKing penetrated 3.25" before yawing and fragmenting. The Alexander Arms Tactical 16 carbine (16" barrel) was used at a range of 100 yards. Impact velocity: 2383 ft/s. Maximum penetration of the 120 gr SMK was 19.5", maximum permanent cavity diameter was more than 6" with lesions running to gel block exterior surfaces. Depth to the maximum permanent cavity was 7.5". The bullet fragmented, with seven large pieces visible within the block. Jacket sections came to rest at 11.75" and 16.25", and the bullet core at 19.5 inch.

The prototype 123 gr SMK penetrated 2" before yawing and fragmenting. The Alexander Arms Tactical 14.5 carbine (14.5" barrel) was used at a range of 50 yards. Impact velocity was 2385 ft/s. The 123 SMK penetrated to a depth of 16.2", maximum permanent cavity diameter was more than 6" with lesions running to block exterior surfaces. Depth to the maximum permanent cavity was 7". The bullet fragmented into multiple small fragments with jacket pieces visible at 11" and 13". A small core fragment was visible at a maximum depth of 16.2"

The 120 gr Norma FMJ penetrated 16.5" before veering out the side of the block and impacting the support frame. No fragmentation was evident, but the slug is believed to have tumbled at about 7" with its maximum permanent cavity at 11 inches. Lesions of more than 6" were torn through the top and bottom block surfaces. The bullet was fired from an Alexander Arms Tactical 14.5” AR-15 rifle at a range of 50 yards with a chronographed impact velocity of 2405 ft/s.

Notes

  1. ^ 6PPC -- The Benchmark of Accuracy
  2. ^ Grendel ballistics table
  3. ^ Four shooters achieve 6.5" group average at 900 yards
  4. ^ 660 yard Sub MOA Group
  5. ^ Armed Forces Journal
  6. ^ Robert Whitley NRA win 5 Mar 05
  7. ^ IHMSA (silhouette pistol) Big Bore Unlimited Champion 2005
  8. ^ 3rd Place behind .308 AR10s - ahead of all .223s (second to last article)

Periodical References (with no online copy)

  • A. Guns 'n' Ammo: Book of the AR-15, 2004, "The 6.5mm Grendel," David Fortier, p. 66.
  • B. Special Weapons for Military & Police, Annual #27 2004, "Beyond the 5.56mm NATO," Stan Crist, p. 62-67.
  • C. Guns 'n' Ammo: Book of the AR-15, 2005, "6.5 Grendel and 6.8 SPC," David Fortier, p. 32-44.
  • D. Shooting Times, February 2005, "Cooking up Loads for the 6.5 mm Grendel," David Fortier, p. 52-56.
  • E. Shooting Illustrated, September 2005, "6.5 mm Grendel and Alexander Arms," J. Guthrie, p. 34-37, 67-69.
  • F. Petersen's: Rifle Shooter, March/April 2006, "Cartridge Efficiency - Why case shape matters," M.L. McPherson, p. 22-24.
  • G. Shooting Times, January 2007, "Other AR Chamberings," Sidebar Article, David Fortier, p. 56.
  • H. Special Weapons, Semi-Annual #50 2007, "The Super Versatile AR," Charlie Cutshaw, p. 44-45, 80-83.
  • I. Special Weapons, Semi-Annual #50 2007, "5.56mm NATO Alternatives," Stan Crist, p. 52-59.
  • J. Shooting Times, March 2007, "Les Baer's 6.5mm Grendel AR Sets a New Standard," David Fortier, p. 26-32.
  • K. Special Weapons for Military & Police #52, Spring 2007, "BETTER-IDEA 6.5mm GRENDEL," Stan Crist
  • L. Special Weapons for Military & Police #52, Spring 2007, "New Battlefield Requirements - New Rifles and Ammo Needed," Charlie Cutshaw

See also

C-Products 26rd Grendel Magazine
Retrieved from "https://en.wikipedia.org/w/index.php?title=6.5mm_Grendel&oldid=161024610"