6.5 Grendel Evolution
November 02, 2011
Considering its intermediate size, the 6.5mm Grendel's performance is superhero-like. Exterior ballistics, retained energy and retained velocity are all a noticeable step up from established intermediate cartridges such as the 5.56x45, 5.45x39, 6x45 and 7.62x39 in the dust. The Grendel hotrods a standard AR-15 platform, allowing it to not only hit harder but also dramatically extends its reach.
I first became aware of the Grendel in late 2002 while working on a 6.5mm project of my own. However I shelved my design after speaking with Bill Alexander, founder of Alexander Arms and who developed the .50 Beowulf cartridge and an AR-15 chambered for the Soviet 5.45x39 M74 cartridge.
Eventually the 6.5mm PPC caught his attention because it would fit his existing high strength .50 Beowulf bolt. So he machined a solid brass 6.5mm PPC dummy round to ponder. It seemed like a fantastic cartridge that was small enough to double-stack in an AR-15 size magazine.
To test the concept, he built a rifle using a free floated 24-inch stainless steel match barrel with a 1:9 inch twist. He fed it using modified USA brand 7.62x39 magazines.
Initial testing revealed the small cartridge to have excellent potential, but unfortunately there was no good commercial source for the PPC case. Then Alexander met Lapua engineer Janne Pohjoispaa, who presented him with the idea for a new cartridge, the 8.6x39 Lapua Tactical. It was basically a .220 Russian case necked up to .338, and Pohjoispaa was looking for someone to make a rifle for it. Alexander instead suggested necking the .220 Russian up to 6.5mm. When Pohjoispaa nodded, the foundation for the Grendel was laid.
The first step was to shorten the neck and increase case capacity. With such a relatively small case, any increase in capacity was a plus. The final change was to thicken the case neck to .012 inch to lengthen case life in a semiauto rifle.
Alexander Arms paid for the cartridge tooling and placed an initial order for 50,000 brass cases in November 2003. About this time I asked Alexander what he planned on calling the new cartridge. ".26 Grendel," he replied. Unimpressed, I suggested 6.5mm Grendel instead. He mulled it over, and the new cartridge was christened.
The finalized 6.5x38 Grendel cartridge has a .441-inch diameter case head and a case length of 1.524 inches. Rim thickness, at .059 inch, is significantly thicker than a 5.56x45. This aids reliability. Shoulder angle is 30 degrees, and a small rifle primer is utilized. Overall cartridge length runs from 2.200 to 2.265 inches.
The Grendel will handle 80- to 144-grain projectiles, but it performs best with bullets in the 100- to 123-grain range. The result is a handsome little cartridge that fits neatly into the confines dictated by the AR-15's magazine well.
Due to its diminutive size one would expect the Grendel to be a purely short-range number like the visually similar 7.62x39, but despite operating at low pressures and midrange velocities, it produces excellent performance due to its use of efficient projectiles with high ballistic coefficients, which shed velocity and energy at a slower rate and deliver higher velocities at target distance.
The next task was getting the new cartridge to shoot. The first throat designs were found wanting, so Alexander took a page from the Swedish Mauser book.
"The 6.5x55mm Swede is peculiar among all the other 6.5mms in that it has a half-degree throat," he says. "This commences right at the end of the chamber neck. The proof is the Swede will shoot just about anything you stuff in it while maintaining a military chamber.
"However the 6.5x55mm is a large case designed for single-base extruded powder. The smaller Grendel has a propensity for double-base ball type propellants. The difference is the double-base propellants are more pressure sensitive.
"Due to this the half degree throat pirated from the Mauser was not building pressure. This worried me regarding secondary detonation in extreme cold conditions, such as Alaska. So we solved this problem by designing the chamber with the back of the throat like a Swedish Mauser and the front like a stock SAMMI design. It was then dubbed a 'compound angle' throat because it has two angles, three if you count the transition from the neck to the throat."
The new chamber design proved not only very accurate but also very forgiving. This latter point is important due to the diverse weight, length and shape of available .264 inch projectiles. All production Alexander Arms 6.5mm Grendel rifles have utilized this compound angle chamber design. Delivery began in late 2004.
Initially Alexander Arms offered four loads: 90-grain TNT, 120-grain Nosler Ballistic Tip, 123-grain Lapua Scenar and 129-grain Hornady SST. Thanks to its ultra high .547 BC and excellent accuracy, the 123-grain Scenar became the standard by which all other Grendel loads are judged. Subsequent introductions include a 130-grain Swift Scirocco, 120-grain Barnes TSX and a 100-grain Berger open-tip match. There's also a military/law enforcement-only load, a 125-grain bullet with a tungsten core.
Wolf Performance also loads the round, although it uses Large Rifle primers. It offers a 123-grain softpoint and a 120-grain Multi-Purpose Tactical, a hollowpoint boattail.
The big news, though, has been Hornady's recent release of 6.5mm Grendel ammunition. The company developed an entirely new .264 inch diameter 123 grain A-MAX projectile specifically for this project. This is blessed with a very high .510 BC. Claimed muzzle velocity is 2,620 fps from a 24-inch barrel.
Hornady's brass uses a small rifle primer, and the company is selling dies, brass and projectiles for reloaders. The cartridge is easy to reload, there's plenty of data, and if you wish, you can form the cases from 7.62x39 brass if you wish.
So what is all the fuss about? A 123-grain .26 caliber slug launched at 2,523 fps from a 16-inch carbine hardly sounds remarkable. However when you crunch the numbers, you find those high BC projectiles smoke the intermediate cartridge competition downrange.
To demonstrate the Grendel's accuracy I put my Alexander Arms 20-inch GDMR (on which I replaced the stock barrel with a fluted Satern match barrel with cut rifling and a 1:8.75 twist) and Mid-Length carbine (standard chrome-lined Government-weight barrel with a 1:7.5 inch twist) to work.
Engaging targets from three to 300 yards with the 16-inch gun is easy. It's light, quick to the shoulder and handles well. Smacking 20x11-inch LaRues from 300 to 600 yards is fairly easy if you keep an eye on the conditions. The Grendel carbine flattens LaRue sniper targets that a 5.56mm 77 grain Mk262 Mod 1 round barely rocks. Wind drift is noticeably less with the Grendel too. Muzzle jump is slightly more than a 5.56mm gun but still easy to control. Reliability is flawless.
While the 16-inch gun is accurate, the 20 inch GDMR is a laser beam. Making rapid hits on multiple targets is easy out to 600 yards. At one point I fired three rounds of Hornady's 123-grain A-Max load in four seconds. All three dropped into just four inches at 600 yards. Four five-shot groups with this load averaged a respectable 4.5 inches at 600 yards.
My 20-inch GDMR has killed any interest I had in a semi-auto .308 precision rifle. It's lighter, handier, recoils less, uses common AR-15 parts, and the ammo weighs less. Plus it will drive a 123-grain Scenar flatter and with less wind drift than a 7.62x51 175-grain M118LR sniper load. It just delivers a lighter payload on target.
I'm not alone in my praise for this cartridge. It has generated interest among U.S. and foreign military groups looking for improved terminal performance and extended reach from a 5.56x45-size platform.
Is the Grendel perfect? No, but considering it's an intermediate cartridge intended for use in an AR-15 platform, it performs extremely well. It will never be a magnum, so if you need more oomph I suggest stepping up to a .260 Rem. However, if you're looking for an AR-15 with more performance than a 5.56x45 can offer, you'll want to consider a 6.5mm Grendel.
6.5 Grendel Velocities
- 100 gr. Alexander Arms Berger Open-Tip Match: 2,847 fps
- 120 gr. Alexander Arms Barnes TSX: 2,551 fps
- 120 gr. Alexander Arms Nosler Ballistic Tip: 2,600 fps
- 120 gr. Wolf Multipurpose Tactical: 2,541 fps
- 123 gr. Alexander Arms Lapua Scenar: 2,627 fps
- 123 gr. Hornady A-MAX: 2,582 fps
- 129 gr. Alexander Arms Hornady SST: 2,450 fps
- 130 gr. Alexander Arms Swift Scirocco II: 2,400 fps
- 100 gr. Alexander Arms Berger OTM: 2,723 fps
- 120 gr. Alexander Arms Barnes TSX: 2,494 fps
- 120 gr. Alexander Arms Nosler BT: 2,535 fps
- 120 gr. Wolf MPT: 2,445 fps
- 123 gr. Alexander Arms Lapua Scenar: 2,523 fps
- 123 gr. Hornady A-MAX: 2,463 fps
- Velocities are averages of five shots measured on an Oehler 35P chronograph 12 feet from the muzzle at an ambient temperature of 90 degrees at 1,030 feet above sea level.
Ballistic Coefficient Comparison
- 77 gr. Sierra MatchKing: 0.362
- 100 gr. Berger OTM: 0.377
- 120 gr. Nosler Ballistic Tip: 0.458
- 120 gr. Barnes TSX: 0.441
- 123 gr. Sierra MatchKing: 0.510
- 123 gr. Lapua Scenar: 0.547
- 123 gr. Hornady A-Max: 0.510
- 129 gr. Hornady SST: 0.480
- 130 gr. Swift Scirocco II: 0.571
- 85 gr. Barnes TSX: 0.246
- 110 gr. Barnes TSX: 0.323
- 110 gr. Nosler AccuBond: 0.370
- 168 gr. Sierra MatchKing: 0.462
- 175 gr. Sierra MatchKing: 0.496
SAAMI adopts 6.5 Grendel