6.5 Grendel Development Notes

January 29, 2004

A Shooter’s Perspective
Arne Brennan, CompetitionShootingSports.com

Historically, the AR15/M16 has not been without controversy and critics. As a military rifle, during early use in the Vietnam War, the M16 suffered from functioning problems due to a change in propellants and improper training of soldiers regarding cleaning and maintenance. Lessons were learned, refinements made and the M16 platform evolved into one of the most prominent firearms in military history. However, the M16 to this day is not without criticism, not so much due to the rifle, but because of the 5.56 NATO cartridge, that lacks the long-range effectiveness of the 7.62 NATO cartridge used in the M14 and other military small arms.

In the civilian market, the AR15 for many years has been considered a casual target and small game rifle again in large part due to its standard chambering in .223 Remington. In formal target competition, it was cast aside as not being a viable option compared to the M14 and it’s civilian counterpart, the M1A, using the 7.62 NATO/.308 Winchester cartridge.

In the 1990s, the AR15 started to appear in the competitive shooting arena and it slowly began increasing its numbers in service and match rifle competition. Use of the AR15 reached a beginning in 199X. During that year, a change in leadership at the US Army Marksmanship Unit mandated change to the current US Army standard issue rifle for use in National Match competition. Following the US Army Marksmanship Unit, various other military shooting teams adopted the AR15 platform for National Match Competition as well. As the 21st century arrived, the AR15/M16 took the dominant position in terms of numbers at many high power competitions including the NRA National Matches at Camp Perry.

While the AR15 has attracted an increasing number of competitive users, its use of .223 Remington cartridges still limits use in long-range competition. To illustrate this point, at 600 yards, the AR15 in .223 Remington requires use of specialized 80 and 90-grain bullets seated beyond magazine length to be competitive. While this adaptation has allowed the AR15 to become a prominent contender in across the course competition at ranges from 200 to 600 yards, when competitors are given a choice of platforms and cartridges, the AR15 is often passed over in favor of cartridges such as the 6mm BR Norma, 6mmXC, and .260 Remington in bolt-action rifles such as the Tubb 2000 or semi-automatic rifles such as the Armalite AR10.

Over the years, a number of AR15 competitors have attempted to overcome this trend by seeking alternative cartridges for use in the NRA match rifle category. In 1998, I like those before me, began this search for an alternative to the 223 that would provide an edge in competitive shooting. In addition, I wanted to explore the idea that a cartridge with such a competitive edge could also be an effective hunting cartridge for whitetail deer, feral hogs and a variety of other game animals.

In the past, one of the most notable alternative cartridges for the AR15 has been the 22 and 6mm PPC. In reviewing these two options, the 22 PPC allowed use of heavy 80-grain bullets needed for 600 yards, but in a magazine length loading. This capability gave a considerable advantage because in theory, one load could be shot across the course simplifying ammunition requirements. However, I didn’t feel the 22 PPC using 80-grain bullets would provide the edge I was seeking and it did not fulfill my hunting capability requirement.

In contrast to the 22 PPC, the 6 PPC was able to fulfill my dual role requirement by using bullets such as the Sierra 107 grain Match King for competition and Nosler Partition bullets in 85, 95 and 100-grain weights for hunting. However, one thing bothered me about the 6 PPC. In my research, I discovered it was necessary to seat the 105-107 grain match bullets back in the case to be within the 2.255-inch length restriction or the front of the magazines needed to be notched to optimally seat the bullet and gain the maximum powder capacity. The thought of notching magazines had zero appeal so before going further with the 6 PPC, I decided to think out of the box.

I knew that Sierra made a 6.5mm 107 grain Match King and Lapua made a 108 grain Scenar and due to the increase in bullet diameter, theses bullets were slightly shorter then their 6mm counterparts. Therefore, use of these 6.5mm bullets would not require seating the bullet back in the case or notching magazines. Interestingly, I found that Lapua also offered a 123-grain Scenar that was the same length as the lighter 108-grain Scenar and had a similar ballistic coefficient to the 6mm 105-107 grain offerings. It became clear that by increasing the caliber to 6.5mm, I could equal the ballistics of the 6 PPC with the 107-grain Sierra and do so without notching magazines or seating the bullet back in the case. In addition, 6.5 mm was easily considered an effective hunting caliber with multiple controlled expansion and polymer tipped bullets in the 100-125 grain weight range available. In theory, it would be a perfect multi use cartridge provided I could equal the velocity the 6 PPC achieved with 105-107 grain match bullets.

In mid 1998, I made the commitment to go with a 6.5mm version of the PPC and contacted JGS Tool to construct a reamer. Since there were no standards for or published history on the 6.5 PPC, JGS Tool constructed a reamer with no throat and provided me with a separate 6.5 mm throat reamer to allow the gunsmith to cut the throat to proper length for my application. Using the final reamer dimensions, Redding constructed a bushing type full length-resizing die. Only thing left was to take the leap of faith and begin construction of a rifle. After speaking with numerous gunsmiths, Scott Medesha of Medesha Firearms undertook the project and delivered a custom rifle in late 2000.

As many readers will appreciate, load development for a wildcat cartridge can be a time consuming experience and this is especially true for a cartridge such as the 6.5 PPC that had no published information available. Taking advantage of the openness of the competitive shooting community, I contacted Dr. Lou Palmisano in early 2001 and discussed my project with him and his theoretical knowledge and guidance as invaluable.

As load development and testing continued, I discovered the 6.5 PPC was very effective and accurate using medium weight 6.5 mm bullets. My initial goal of achieving 2650 fps was surpassed as I developed loads using moly coated Cauteruccio 128-grain bullets achieving 2750-2800 fps. My project was a success, but little did know that it was to take a new direction.

In early 2002, I contacted Lothar Walther to speak with them about getting a barrel blank. Rather then just sell a barrel blank; they spent time learning about what my application to be sure that I got their best barrel configuration for my needs. Interestingly, during the conversation, they kept introducing Alexander Arms to the discussion. I had heard of Alexander Arms through a friend of mine who was interested in their .50 Beowulf cartridge for hunting, but had never given much thought to it because I was primarily a long-range paper puncher. Lothar Walther introduced Alexander Arms into the conversation so often with the suggestion that I speak to them; I finally had to tell them I really had little interest in a .50-caliber AR15 cartridge. Their response was they knew that, but they were positive that I would really enjoy speaking with Bill Alexander. Ironically, a few days later, the friend with an interest in the .50 Beowulf asked if I could learn more about the Beowulf to help him decide whether it was a good direction for him to take. I agreed to find out what I could and picked up the phone and called Alexander Arms and spoke to Bill Alexander about his .50 Beowulf creation. The point came where discussion on the Beowulf was almost complete and I told Bill that I had spoken to Lothar Walther and they were insistent that I call him, but I really didn’t know why since I was focused on my 6.5 PPC AR15 match rifle. A few moments of silence later, Bill Alexander response to this was, “You have a working AR15 in 6.5 PPC?” I said, ”Yes,” and what had been a 15-minute conversation became an enthusiastic discussion lasting another 3 hours and a shooting relationship that continues to this day.

A Designer’s Perspective
Bill Alexander, Alexander Arms, LLC

In early 2001, as chief engineer for Alexander Arms, I was finalizing the .50 Beowulf cartridge and rifle that became the first civilian product of Alexander Arms. The .50 Beowulf was intended to deliver raw power on targets out to 200 yards with 1-2 MOA accuracy out of a 7 lb short barrel AR15-type rifle. Needless to say, the .50 Beowulf is about brute power and in this it excels. However, what the .50 Beowulf lacks is the ability to reach out to targets that are just dots on the horizon to most people. As a manufacturer who specializes in unique firearms solutions, the next mission became to develop a tool for long- range precision shooting in AR15 type rifles. During a business lunch, I outlined my objectives and goals on a napkin and tucked it away to ponder what could be possible.

As an engineer with a background in defense projects, it is not uncommon to develop systems and solutions beginning in theory with a clean sheet of paper. In beginning this new project, the only known requirement was that this new cartridge would be a long-range performance cartridge for use in the AR15 type rifles. As such, the engineering parameters of the AR15 system became the boundaries of development. Factors to be considered in this development included cartridge overall length, chamber pressure, bolt thrust and reliable functioning from the magazine.

In the initial phase of development, a wide variety of calibers were evaluated from 6mm through 7.62mm with the most promising being those between .25 caliber and 7mm. Of these the 6.5mm had the most efficient bullet designs in the weight range that could be effectively launched from a cartridge that would fit within the design constraints of an AR15 type rifle. With the decision made of caliber, the development moved towards the design of a cartridge case. Calculations of time vs. pressure curves were developed for a theoretical cartridge and how it would work within the AR15 rifle operating system. The details of such work are generally boring so I will not repeat then here but suffice to say the resulting theoretical cartridge was none other then a 6.5mm version of the legendary PPC. As a design engineer, it was clear to me that the original designers of the PPC cartridges had developed something special well suited to the application on hand.

Every now and then an engineer gets lucky. It was early in 2002, I had the designs for a new cartridge out to contract and I was holding my breath that the damn thing would do what it is supposed to. A phone call was passed through to me of a customer wanting technical information on the Beowulf rifle he was considering purchasing, having been referred by Lothar Walther. We spoke for a while regarding the Beowulf and then he mentions he has a 6.5mm PPC wildcat in a custom built AR15 that he has been shooting since 2000. I have the whole population of the US who could ring about a rifle but I get the one guy who has actually built what I have been working on. I wouldn’t bet beer on those odds. Suffice to say the phone call lasted longer than expected and Arne Brennan, who was the customer, has become a regular conspirator in the works to get the 6.5 Grendel to market.

The AR15/M16 platform was designed for the 5.56 NATO cartridge. As such, design changes were required for the change to a larger diameter cartridge such as the 6.5 PPC. Taking from my own experiences building the .50 Beowulf along with the practical experience gained by Arne Brennan with his custom built 6.5 PPC, the development process was streamlined and the necessary components were engineered and constructed including bolt assembly, barrel extension and magazines.

In May 2003, the first 6.5 Grendel prototype rifle was unveiled to the world during an event at the Blackwater training center. The rifle and cartridge delivered outstanding accuracy with total reliability. Feedback was gathered from a number of people permitted to shoot the prototype rifle.

As most readers can appreciate, a custom built rifle is not a production rifle. So a rigorous period of testing and refinement began to advance the project into production. One of the key refinements came as a result of Lapua and their team of engineers joining the project and presenting improvements in the case design intended to optimize performance for 107-130 grain 6.5mm bullets and use in semi-automatic and automatic platforms such as the AR15/M16. As time progressed, the necessary production test runs of rifles and ammunition continued to ensure that the production products are as good or better then the custom built prototypes. Months of testing and thousands of rounds of ammunition later, the 6.5 Grendel is reality and ready for the world.

The 6.5 Grendel is an evolution of the 6.5mm PPC optimized to seat 107- to 130-grain match bullets at an overall loaded cartridge length of 2.255 inches. Case length was kept to 39mm or 1.505 inches as in the original PPC. Studies found that using a slightly longer case would lead to seating bullets deep in the case and would at the very minimum limit the bullets usable to only a few offerings. The case body is perfect in length to stabilize the cartridge in the magazine and prevent tipping without having to resort to special and normally jam-prone followers. In addition, the case diameter is the maximum dimensions that allow a double column feed.

Powders suitable for this case size typically are close to 100% load density created optimum conditions for uniform combustion. In developing production ammunition and measuring the internal pressures when firing such loads, the instruments report back mean average pressures in the range of 42,000 psi. Given that the rifle will safely operate and pass long-term fatigue tests at pressures of 45,000 psi, the internal pressures for production ammunition are mild to the delight and relief of both engineers and insurance agents. More impressive is that at these mild pressures, a consistent muzzle velocity of 2600 fps is achieved with a 123-grain bullet. Shoot a string of 10 rounds however and something magical happens. Velocity figures with corresponding pressure curves do not change shot to shot. Typically, a 10-shot string has a maximum spread in the low single digits and the bullets strikes form a single clean hole in the target. For the rifle itself the steady pressure allows the gas operation to be finely tuned such that the bolt carrier impulse is identical shot to shot and the parts move at close to optimum design speed. Ejection patterns are consistent and the whole operations cycle becomes reliable and repeatable as the parts are always doing the same thing at the same speed.

One of the great benefits of 6.5mm caliber is the high coefficients of drag (Cd) for given bullet weights making them ideal for long range shooting. The 6.5 Grendel is no exception.

The 123-grain Lapua Scenar with a ballistic coefficient of .547 launched at modest 2600 fps muzzle velocity delivers outstanding long range performance out to 1200 yards. Accuracy levels were impressive with test rifles forming single digit groups at 1,000 yards and at 600 yards, tennis ball sized targets are easy prey with a scope adjustment of only 14 MOA with a 200-yard zero.

In ballistic gelatin tests, the Lapua 108-grain Scenar launched at a muzzle velocity of 2750 fps penetrated 22" of gelatin with a .43" diameter and 64% weight retention at a distance of 300 yards. As a more casual test, the Lapua 108-grain bullet consistently sliced through 4" pine posts at 900 yards.

In the interest of game hunting, the 120-grain Nosler Ballistic tip at a 2600 fps muzzle velocity was tested in ballistic gelatin. This bullet penetrated 18" and expanded to .51" diameter with 75% weight retention at a distance of 300 yards. The recovered bullet exhibited perfect mushrooming with no core separation.