sending...Updates:
Go to Relative Drop and Drift (3-30-13)
Go to Case Length (5-14-13)
Introduction:
20 Grendel with BlackHole Bullets Diamond Tip Rebated Boat Tail Bullet
Have you ever thought about having an AR-15 carbine that shoots flatter and has about the same wind drift as long range .308 Winchester target loads even at 1000 yards while keeping the recoil to the same or less than many .223 Remington loads? The .20 Grendel may be the cartridge that gives a new understanding of long range shooting with the AR!
The idea originated from a conversation with Bill Alexander, the developer of the 6.5 Grendel. A lot of analysis, discussions and thought later, the cartridge took shape in a deceptively simple format. The idea is to get a long-range .20 caliber cartridge suitable for implementation in AR-class rifles and is based on the 6.5 Grendel.
We thought of ways to help new shooters get started in this cartridge where factory brass is still a vague possibility. One of these was to design the cartridge so that the cases can be formed with as few steps as possible. This resulted in keeping all of the dimensions of the Grendel constant except for those needed to get a neck that handles .20 caliber bullets.
The cases are formed by first by running them through an intermediate forming die followed by running through the .20 Grendel full-length sizing die. For now we are using a 6mm PPC full-length sizing die as the forming die. The chamber neck is sized to permit a no-turn neck in the cartridge. This means the only additional case prep needed is an aggressive inside and outside neck chamfer exercise.
The rifle being used for load development is a Savage Model 16 with a 20-inch barrel. The bolt gun simplifies some of the complexities involved with doing the whole thing in an AR frame. I get a measured 3100 ft/sec with 55 grain bullets at an estimated 50,000 psi per QuickLoad using H414. QuickLoad calculations suggest that some other powders might get 50 ft/sec faster with the same general pressures. Some of them will be explored in due course.
I am grateful to the small community of people who helped make this project possible. While not everyone can be listed for privacy reasons, my thanks still go out to you.
These folks created the hardware needed to make the 20 Grendel and have permission to use my specifications for new work:
- Reamer by Dave Manson
- Barrel by Pac-Nor Barrels (Recommend 8-twist or faster for these heavy bullets!)
- Dies by Ben Syring at Hornady (bsyring@hornady.com)
The ballistics of this cartridge are interesting and I hope to be able to add tables and graphs to this page in addition to reporting experiences as we explore what the cartridge can do with pressures and barrel lengths appropriate for the AR-15 platform.
Should you want more information sooner, feel free to drop an email to jsmith@shootersnotes.com with your questions, comments, and suggestions.
Relative Drop and Drift (3-30-13):
The introduction tells us that the 20 Grendel might be an interesting cartridge for long range shooting with the AR-15. The comparisons here all have velocities expected for 20-inch barrels. To be sure, a long range competitor with the .308 Winchester or especially the 300 Winchester Magnum will use a 26-inch or longer target barrel to get as much velocity as practicable. But then, so would someone contemplating the the 20 Grendel for long range competitive target shooting with an AR or bolt gun. The principal focus here is on long-range varmint hunting with potential competitive shooting as a secondary possibility.
It is easy to skew performance comparisons by using a sleek VLD bullet for one caliber and more conventional bullets for the other. Here, the .223 Rem, .308 Winchester, and .300 Winchester Magnum loads are based on typical 24″ barrel factory loads with Sierra MatchKing bullets and the .20 Grendel is based on test data with 55 gr Match Grade BT Long Range Varmint bullets. These bullets were judged to have similar enough shape factors for the comparisons to be valid.
We can see that, with the selected loads, the 20 Grendel wind drift at 600 yards would be almost indistinguishable from that of the .308 Winchester. Similarly, the differences between the 20 Grendel and the 300 Winchester Magnum are small enough that they will be seen only by the most competitive target shooters. This correlation translates easily into the varmint hunting arena by recognizing that less wind uncertainty exists with this cartridge than with most other low-recoil varmint guns. For many, if not most, long range varmint hunters, the reduction in recoil allows for many shots to be taken without recoil fatigue becoming an issue.
The 20 Grendel is also the flattest shooting of the cartridges considered in these charts.
One might ask “What about the .204 Ruger?” The difference is that the 20 Grendel has a shorter case with a little more volume than the Ruger. This means that the Grendel can readily accommodate the long-nosed heavy bullets that won’t be useable in the Ruger at cartridge lengths suitable for the AR-15. For this reason, the 55 gr Berger has 20% less drift at 600 yards even when running at around 50,000 psi.
Case Length (5-14-13):
Trim cases when the length exceeds 1.530 inches. The trim to case length is 1.524 inches per the case drawing. I am using the factory-set length of the 6.5 Grendel version of World’s Finest Trimmer from Little Crow Gun Works. The exercise helped tighten groups.