AR-Fu: Introducing the .277 Wolverine


When Eugene Stoner originally designed the first prototype that was to become the AR-15, it was not the smaller 5.56 caliber design, but rather the 7.62 caliber design. While the first trials with these larger caliber units impressed the military, the world trend at the time was moving towards the smaller caliber 5.56 Nato.

Classic M16

The belief was that the smaller caliber 5.56 design enabled a soldier to have reasonable lethality, while being able to carry more ammunition. More so, the smaller frame and weight of the lower caliber ammunition lightened the already burdened solider’s load.

The history of the M16/AR-15 is a long and storied one. This story is already well documented, so we will not dwell on it here. In making the decisions to reduce the caliber to the diminutive 5.56, military leaders made the longer term ballistics capabilities of the AR-15 platform limited. No one foresaw the emergence of the military M16 into the AR-15 and the Modern Sporting Rifle (MSR) concept that it has become today. For many years, the AR-15 platform was thought to be limited to the smaller 17 and 20 caliber bullet ballistics and profiles. This view stayed in place until the late 1990’s and early 2000’s when the “real world” need (in the military) drove the prototyping of 6 mm, 30 and 40 caliber bullet usage. This innovation lead to the 6.8 SPC, the 300 Blackout/AAC, the 458 SOCOM, as well as other calibers in the M4/M16/AR-15 platforms.

With the civilian adoption of the AR-15 platform, and its transformation into the “Modern Sporting Rifle”, even more innovation has taken place.  Forums, such as Modern Sporting Rifle Evolution (, have become advocates for pursuing the full capability and ballistics options of the AR-15 platform. As a result, many new “wildcat” calibers have emerged for the AR-15.

What the Heck is a Wildcat?

What the heck is a wildcat? “Wildcatting”, at least in the gun world, consists of going out on your own and building a caliber/cartridge/load that is not standard.

Sounds simple doesn’t it? Well it isn’t!

277 Wlv Build (courtesy of MSR Forums)

First, let’s take the cartridge. To design a new cartridge requires investigating and specifying load specs, cartridge geometries, and projecting ballistics in the most “nitty-gritty” of details. A wildcatter must design nearly every aspect of the cartridge. Yes, there have been some (such as the 7mm-8mm) that started as simply “necked down” versions of different calibers, but even that requires determining powder type, burn specifics and load to make it work optimally.

Second, given that many of the “low hanging fruit” wildcats have already been developed and/or turned into standards (or realized to be boondoggles), modern AR-15 wildcats involve re-engineering nearly every detail of the cartridge and chamber geometries.

Third, the work is not over once the cartridge is specified – barrel profiles, chamber designs and bolt considerations have to be determined. Until the innovation of the 6.8 SPC and some other bigger cartridges, the only bolt design that was generally available was the standard AR-15 bolt. Though that has changed, options are still limited and manufacturers are sporadic.

So there is gold at the end of this rainbow, right? Wrong!

Out of any 100 wildcat cartridges designed, maybe 1 or 2 make it into a SAAMI standard. That path (SAAMI standard), in and of itself, is costly and wrought with its own issues.

Wildcatters are like mad hatters!! Wildcatting a caliber is an act of love, and involves some insanity!

.277 Wolverine Specifics

In 2014, Mark Kexel of Mad Dog Weapon Systems embarked upon a journey of insanity. He wanted to make a 6.8 caliber round that did not entail all of the special bolts, the magazine and other modifications that the 6.8 SPC required. More so, many people found the original bolt designs of the 6.8 SPC (Gen 1) were fraught with failures. In spite of the issues, the 6.8 SPC had a fierce following and, overall, the caliber had proven itself to be a really solid round for the AR-15/MSR.

Enter Mark… From what I have read, Mark was originally a big advocate of “barrel only” wildcat rounds (this is apparent from the other wildcats that he has developed). “Barrel only” wildcat rounds are what they sound like – all you will need to change on any AR-15 platform is the barrel, every other part is standard. The 300 Blackout had become a big hit and showed the MSR community that good wildcats could be developed that did not require specialty bolts or other modifications.

From the original posts Mark made on various forums announcing his wildcat direction, it seems he felt as though the 6.8 mm bullet (or .277 caliber as his wildcat was later re-named) was ideal to produce both the super and subsonic ballistics that the 300 Blackout/AAC rounds had attempted to produce. For those readers who may not be up to date with these calibers, the 300 Blackout had been designed as a “barrel only” caliber for the AR-15 .  The 300 Blackout was supposed to have ballistics that were solid in both super subsonic ranges. What was discovered was that both were mediocre, with the subsonic ballistics being far more mediocre than the supersonic ballistics.

Mark felt as though he could produce a round, using the .277 caliber bullet (6.8 mm), that would attain the original goals of the 300 blackout. As stated in his original postings, his goal was to produce a CQB/Mid-range cartridge using the 6.8/.277 bullet – no bolt change, only barrel change.

Courtesy Mad Dog Weapons Systems, LLC

In March of 2013, the .277 Wolverine was born with this post in the 6.8 Forums.

My Experience

In early 2015, I ran across the .277 Wolverine information and read up on this wildcat.  I, also, went over to the Mad Dog Weapons web page to review more information. I was looking to build a “wildcat”, having personally built some 300 Blackouts and other non-standard AR-15 guns. I liked the 300 Blackouts, but the performance was lacking in ranges beyond 150-200 yards. I overheard someone once characterize the 300 Blackout as a modern “Tommy Gun” (this is a “so true” analogy).

I was looking for an AR-15 round that could go from hogs, to deer, to coyote, to… pretty much anything small to medium game (large game for me are elk+).

Like many others before me, I also found that the 300 Blackout was essentially a 50 yard subsonic round. I wanted something with a bit more distance, subsonic wise.

So, I took the bait and purchased my barrel and kit to build a .277 Wolverine.

I will NEVER regret that choice. I love the round!

Here are some of the highlights of the .277 Wolverine:

  • Barrel only change – everything else is stock AR-15/5.56 parts
  • Works well over a range of barrel sizes from 10″ – 20″
  • 85gr/3000 fps, 90gr/2900 fps, 100gr/2700 fps, 110gr/2650 fps
  • Subsonic weights up to 200 grains
  • Production ammunition available from sources
  • Open sourced the specification of the wildcat
  • Pursuing SAAMI standardization

Great… but is it effective? Over the course of the last eighteen months, I have used the original .277 Wolverine that I built to hunt coyotes, deer and hogs. This past season, I took down a nice whitetail deer in my home state at 60 yards. The animal anchored immediately (unfortunate, since it was in the middle of a 3 foot deep boggy, swamp)!

277 Wlv Blueprints

All said, I have yet to be disappointed by the ballistics of this round. It generally has a 0-250/300 yard effective range – but don’t let that fool you. Guys are reporting good groupings beyond 500 yards. The ability to load down into the 85 grain range up to the 130 grain range and stay supersonic is excellent. Plus, across those ranges, the 6.8/.277 caliber has a great ballistics profile that keeps its energy down range.


As “Hannibal” Smith used to say in the A-Team, “I love it when a plan comes together”.  Mark’s drive in delivering a wildcat round that was valuable to the AR-15 community has resulted in a plan coming together. That plan is the .277 Wolverine. If you have not jumped on the .277 Wolverine bandwagon, you may want to get on!  The day is coming where you may see more and more AR-15s in this caliber than any other caliber!

Final thought… It takes guts, ingenuity, conviction and courage to attempt, much less succeed,  in making a wildcat cartridge go from a “good thought” to a SAAMI standard. Big shout out to Mark Kexel for making this happen for the .277 Wolverine!

Check out this awesome interview we had with Mark Kexel on our Guns Smoking Brass Flying Episode #3


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