The .277 Wolverine (6.8x39mm), also sometimes abbreviated .277 WLV, is a wildcat cartridge based on the 5.56x45mm NATO round and was designed by Mark Kexel of Mad Dog Weapon Systems in 2014. It is a versatile mid-powered cartridge with better ballistic performance over the AR-15's traditional .223 Remington / 5.56×45mm NATO chamberings. Converting from .223 / 5.56 to the .277 Wolverine requires only a new barrel. It utilizes small rifle primers, as well as .277 caliber projectiles (like the similar 6.8 SPC, the .270 Winchester, as well as the highly anticipated .27 Nosler and .277 Fury).
One major difference between the .277 Wolverine and cartridges such as the 6.5 Grendel or 6.8 SPC, is that the Wolverine is directly based on the 5.56 cartridge and is merely necked up to accept a larger caliber bullet. This is the same design philosophy used on rounds like the .300 Whisper and .300 Blackout. As a result, the round can feed from a standard AR-15 / STANAG magazine. It also means that magazine capacity is not hindered in any way.
Design and Development
The .277 Wolverine was developed by Mark Kexel of Mad Dog Weapon Systems in 2014. Per an interview, said: "I liked the performance of the 6.8 SPC and the versatility of the 300 Blackout. After researching both of them extensively, and having a lot of conversations with many, many experienced professionals and enthusiasts, I decided to move forward with a new cartridge design that would hopefully combine the attributes of both, and dismiss the deficiencies."
For similar reasons that a .277 inch (7.04 mm) diameter bullet was selected for the 6.8 SPC (ideal mass-to-diameter-to-length for mid-weight bullets constrained to loading in an AR-15/M16 STANAG magazine), 6.8mm became the caliber for this new AR-15 wildcat cartridge. Like the .300 AAC Blackout and unlike the 6.8 SPC and other "larger bore" AR-15 cartridges, the .277 Wolverine is based on the widely available 5.56×45mm parent case. Therefore, rifle components such as the bolt and magazine are fully interchangeable between 5.56×45mm and .277 Wolverine firearms, and AR-15 magazines can be used with zero loss in capacity. Overall, a new barrel is the main component needed to be changed in order to convert a standard AR-15 to .277 Wolverine.
To load heavier (longer) bullets to magazine length without problems seating the bullet's ogive into the case mouth, the Wolverine case is shortened to approximately 39 mm from its 45 mm parent brass. The case is resized and formed in a single operation to create a new 23-degree shoulder and a larger neck.
Initially intended as a proprietary cartridge, MDWS publicly released the detailed chamber and headspace gauge specs and drawings for the .277 Wolverine cartridge in June 2015.
At first, the design focused on optimal performance with supersonic bullets in the 85-115 gr (5.5-7.5 g) weight class. As a result, a 1:11 twist rate barrel with 5R Rifling was initially selected. Subsequent consumer interest in firing "heavy-for-caliber" subsonic bullets led to the design, testing, and production of 1:7 twist barrels in order to stabilize the longer and heavier projectiles.
- Parent case: 5.56 NATO
- Case type: Rimless, Bottleneck
- Bullet diameter: 0.277 in (7.04 mm)
- Neck diameter: 0.3089 in (7.85 mm)
- Shoulder diameter: 0.356 in (9.04 mm)
- Base diameter: 0.377 in (9.58 mm)
- Rim diameter: 0.378 in (9.60 mm)
- Case length: 1.530 - 1.535 in (38.86 mm, trim) to 1.545 in (39.24 mm, max.)
- Overall length:' 2.26 in (57.40 mm) max. COAL (typical)
- Rifling twist: 1:7 (subsonic/supersonic), 1:11 (supersonic)
- Primer type: Small rifle
The .277 Wolverine has almost similar performance to the 6.8 Remington SPC with 110 gr (7.13 g) projectiles, achieving similar muzzle velocities of 2,500 fps (762 m/s) vs. 2,700 fps (823 m/s). The smaller case of the .277 Wolverine is more efficient and also has less recoil due to a smaller propellant load.
Using lighter bullets in the 80-90 gr class (5.2-5.8 g), the velocities were a bit slower than typical 5.56×45mm rounds, but the .277 Wolverine provided substantially increased energy due to greater bullet mass, along with the added benefit of a larger caliber bullet. As it pertains to energy, 60-62 gr bullets (3.9-4.0 g) from a 5.56×45mm round typically provide less than 1,200 ft lbs (1,627 J) of energy, while 85-90 gr bullets (5.5-5.8 g) from a .277 Wolverine round provide over 1,500 ft lbs (2,034 J) of energy (measured at the muzzle of a 16-inch barrel).
There are always trade-offs between cartridge size, bullet diameter and weight, muzzle velocity, and energy on-target (at any given range). The .277 does not replace .308 Winchester (7.62×51mm NATO) or .270 Winchester for long-range shooting. However, it easily outperforms the .223/5.56 at typical hunting ranges and approaches the 6.8 SPC while using less expensive components (brass, magazines, bolt, less powder per load) along with having lighter recoil.
The following section shows ballistic performance of various .277 Wolverine loadings.
|Bullet Weight / Type||Velocity||Muzzle Energy|
|85 gr (6 g)||2,800 ft/s (850 m/s)||1,480 ft lbf (2,010 J)|
|90 gr (6 g)||2,750 ft/s (840 m/s)||1,510 ft lbf (2,050 J)|
|95 gr (6 g)||2,650 ft/s (810 m/s)||1,480 ft lbf (2,010 J)|
|100 gr (6 g)||2,600 ft/s (790 m/s)||1,500 ft lbf (2,000 J)|
|110 gr (7 g)||2,500 ft/s (760 m/s)||1,525 ft lbf (2,068 J)|
Ballistic Performance Compared to Other Cartridges
The table below provides performance data for several factory AR-15 class cartridges, including the 5.56, 7.62x39, .300 Blackout and .277 Wolverine. Based on the data below, it appears that the .277 Wolverine truly is an excellent mid-point between the 5.56 and the .300 Blackout, offering a compromise between the increased range and velocity of the 5.56, and the increased ballistic performance of the .300 Blackout, although it has more energy than either cartridge. It also retains energy better than either cartridge. Further, the .277 Wolverine has better access to high ballistic coefficient bullets. They'll also stabilize better than .300 Blackout loadings, and will stay supersonic for longer if that is required for the application. The 6.8 SPC seems to depart from fitting that middle ground role between the aforementioned cartridges, though it certainly does have some advantages of its own.
|Round||Bullet Weight||Barrel Length||Muzzle Velocity||Ballistic Coefficient (G1)||Energy at 300 Yards|
|5.56×45mm (M855)||62 gr (4.0 g)||16 in (410 mm)||2,900 ft/s (880 m/s)||0.304||579 ft lbf (785 J)|
|7.62×39mm||123 gr (8.0 g)||16.5 in (420 mm)||2,300 ft/s (700 m/s)||0.300||633 ft lbf (858 J)|
|300 BLK||110 gr (7.1 g)||16 in (410 mm)||2,300 ft/s (700 m/s)||0.300||622 ft⋅lbf (843 J)|
|300 BLK||125 gr (8.1 g)||16 in (410 mm)||2,200 ft/s (670 m/s)||0.320||644 ft⋅lbf (873 J)|
|.277 Wolverine||90 gr (5.8 g)||16 in (410 mm)||2,750 ft/s (840 m/s)||0.275||736 ft⋅lbf (998 J)|
|.277 Wolverine||100 gr (6.5 g)||16 in (410 mm)||2,600 ft/s (790 m/s)||0.323||754 ft⋅lbf (1,022 J)|
|.277 Wolverine||110 gr (7.1 g)||16 in (410 mm)||2,500 ft/s (760 m/s)||0.370||837 ft⋅lbf (1,135 J)|
The .277 Wolverine provides similar ballistic performance to the 6.8 SPC for accuracy, hunting (varmints to medium-game), target shooting, and home/personal defense. 277 caliber / 6.8mm bullets are readily available from all major component manufacturers such as Speer, Sierra, Hornady, Nosler, Barnes, Remington, Winchester, Woodleigh, Lehigh Defense, Hawk and so on. Likewise, they come in a wide range of bullet weights from 85 to 200 grains (5.5-13 g) and styles useful in the .277 Wolverine - including practice or fun, competition target shooting, varmints, defense, and hunting.
The complete bolt carrier group (carrier, bolt, firing pin, and cam pin) and charging handle can be swapped between the original 5.56×45 and the .277 Wolverine upper.
Commercial Availability, Reloading etc
At least four commercial manufacturers have produced .277 Wolverine-chambered barrels, largely for AR-15 conversions – although MDWS also sells barrels for Savage and Remington bolt-action rifles. Barrel makers include: X-Caliber, McGowen, AR Precision, and PAC-NOR. By the end of April 2016, more than 1,000 .277 Wolverine barrels had been sold, with more than 2,000 sold by mid-November 2017. Barrels lengths include: 8.2", 10.5", 12.5", and 14.5" inch pistol barrels, as well as 16", 18", and 20" inch rifle barrels.
.277 Wolverine cases can be easily made by any reloader using extremely common and inexpensive 5.56×45mm brass, which need to be shorted and resized. Extensive reloading data (including chronographed velocity, accuracy, and ballistic gel testing) appears to be readily available. Brass casings and/or loaded ammunition was available commercially from several sources, including: JB's Firearms, LLC and Outdoor Shooter Supply, however it appears that as of 2021, both are out of business. Reloading dies and tools are available from Hornady, Lee Precision, Sheridan Engineering, CH4D, and Little Crow Gun Works. The fire-formed .277 Wolverine case holds approximately 27.5-27.8 gr of water, compared to 28.5-28.8 gr for the parent case.
In October 2017, Starline produced 50,000 newly manufactured cases head-stamped ".277 WLV" for MDWS; all were sold in under 72 hours of posting. Starline still lists the .277 Wolverine on their website as a standard offering as of 2021.