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The .277 Wolverine: Birth of a Wildcat


One of the major goals has been to come up with something that is a significant boost in performance over the 5.56, but requires the least amount of proprietary hardware to make it work.  Enter the .277 Wolverine.  All that it needs is a simple barrel swap.  Virtually everything else is box stock 5.56 AR-15 hardware.  You can’t get any simpler than that.



by John Hull

Copyright 2014


Nobody knows what the first wildcat cartridge was, or who came up with it.  We don’t know what the motivation was behind it.  But, we can say with certainty that wildcatting cartridges has been around almost as long as metallic cartridges and reloaders.


From left to right: 5.56 NATO, .277 Wolverine, 300 AAC Blackout and 6.8 SPC

From left to right: 5.56 NATO, .277 Wolverine, 300 AAC Blackout and 6.8 SPC

The reasons for wildcatting are as many as there are cartridges.  Improved performance is probably the biggest one, but it could also be filling a gap in the caliber lineup for a particular type of firearm.  It could be because its obsolete and no longer in production, so you have to use a different case to get to the one you want.  It could just as easily be ‘just because’ nobody else has done it yet.


Since most wildcatters are individuals working alone, it is easy to end up with many versions of the same basic idea, all blissfully unaware that others had the same idea and ran with it.  Some designers, like P. O. Ackley, had ideas that were unique enough to become famous, even if the result didn’t always  result in much improvement to the original.  The realm of the wildcatters has mostly been bolt rifles, at least up until the advent of the AR-15.   That’s where our story begins.


If you have paid attention even a little bit, you know that the popularity of  the ‘black rifle’ or ‘modern sporting rifle’ has exploded in the last ten years.  It is, by far, the most popular rifle in use today and there is a bewildering array of variations in both hardware, and calibers.  If you are new to MSRs (modern sporting rifles), deciding what to buy, where to buy it, and what caliber to get can be daunting.



The default is, and always has been, your basic 5.56×45 caliber, A2/M4 clone.  There are dozens of places to buy parts if you wish to build your own, and there are tons of surplus ammo available at reasonable prices.  But, as the Army has found out since it first introduced the M-16 50 years ago, the 5.56 has limitations.  Even with the improvements in ammunition over the last five decades, those limitations have spawned a robust community of wildcatters trying to improve on the original.  The result is literally dozens of cartridges ranging for .20 caliber to .45 caliber, and in power from the .22 Long Rifle, to the .458 Socom (roughly equivalent to the .45-70).  This is all in the AR-15 platform.  It is hard to get through a week without seeing something about a new ‘cat, whether for the AR-15 or the AR-10.


One of the major goals has been to come up with something that is a significant boost in performance over the 5.56, but requires the least amount of proprietary hardware to make it work.  Enter the .277 Wolverine.  All that it needs is a simple barrel swap.  Virtually everything else is box stock 5.56 AR-15 hardware.  You can’t get any simpler than that.


The Interview


wolvmark72The Wolverine is the brain child of Mark Kexel of Mad Dog Weapon Systems.  He started out with a 6.8 SPC II and fell in love with the .277 caliber – with good reason, because the 6.8 is the premier deer and hog hunting caliber in use in the AR platform and #2 in sales behind the 5.56.  He wanted something that would give a big increase to the performance of the AR over the same ranges and uses as the 5.56, but with as few changes in hardware as he could get away with.  All that is required to create the Wolverine is to run 5.56 brass into the sizer die to open the neck to .277 caliber and form the new shoulder.  Then you trim the excess neck to the required length.  After that, it is just like any other case.  Chamfer and deburr the neck, prime the case, load powder, and seat the bullet.


I sat down with Mark to find out more about how he got the idea for the Wolverine, and how he shepherded it from paper to the rifle range.


Tell us a bit of your personal history, how you got into shooting, and what skills you brought to the hobby.

When I was very small, perhaps 6, my Dad let me shoot his .22 rifle off of his shoulder while he knelt down so that it was at the right height for me.  He then bought me a BB gun, and I used to shoot at pie tins tied to the backyard fence that bordered a forest preserve.  I grew up reading Field & Stream, and Guns & Ammo.  I bought my first shotgun when I was 18, my first handgun when I was 21.  I lived in Illinois, and there is no rifle hunting for Deer in Illinois.  I bought my first rifle at around 22, and it was an SKS because that’s what I could afford.  I still miss that rifle, it shot pretty well actually.  The only skill I may have brought to the hobby was patience, but I’m not so sure that’s a skill.  Like everyone else, I started with no skills, and was taught, and taught myself along the way as well.  Although my participation in the sport has had its peaks and valleys, due to the normal challenges in life getting in the way sometimes, it is my passion.

You’re only 40 years old, and relatively new to handloading and cartridge design by your own admission. What was it that sparked the desire to jump into the deep end of the pool, so to speak, and create your own cartridge?

wolvmagcart72I am extremely new to hand-loading; have only been doing so for just under a year at this point.  I have the same amount of experience in cartridge design as I have in hand-loading – practically none.  The history of the .277 Wolverine goes back to my youth.  The cartridge was conceptualized after reading so many articles about the pros and cons of both the 5.56 NATO cartridge and the 7.62x39mm cartridge.  They both had their attributes and their deficiencies.  I’ve always thought to myself that there should be an “in between” cartridge, but up until recently I had no idea on how to go about making it happen.  I followed the development of the 6.8SPC and the 300 Blackout, and neither of them were exactly what I was looking for.  I like the performance of the 6.8SPC 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.

Once you got started on creating the Wolverine, what were some of the major hurdles you had to overcome?

This is an easy question to answer.  My biggest hurdle was ignorance.  Put more gently, a lack of experience.  Now that I’ve done it once I will save myself a lot of headaches, and money, on the other projects I plan to undertake.  Thankfully, I had a lot of folks out there ready and willing to help.  I needed a reamer drawing, and Harrison from AR Performance came through.  I needed referrals to reamer and gauge makers, and again he came through.  I needed input, feedback, conceptual cartridge drawings, projected performance calculations, and many, many more things I didn’t even know I would need.  My friends in the shooting community all stepped up and helped out.  We (the shooting sports enthusiast community), are a very bonded group and most people are willing to help another to support the sport and developments within.  Financing the development of the cartridge was not easy either.  It costs a lot of money to get reamers, gauges, tests barrels, loading supplies, and other ancillary items together to undertake a project like this.  Thankfully, I have a good job and even better, an understanding wife who believed in me and what I was doing.  (Thanks Jill!)

You’ve also got a website,, selling Wolverine components, and high quality AR parts for the 6.8 SPC, and the 5.56 calibers. How is that going?

Yes, I have an actual company now.  Mad Dog Weapon Systems, Inc. (MDWS).  Things are going pretty well.  It’s only my first year so I’ll be looking to grow and expand as the market allows.  Most of the items I currently carry hover around AR upper-half building, as I thought it would be nice to provide a one-stop-shop experience for those looking to build their own .277 Wolverine, 5.56, 6.8, .308 and 300BLK uppers.  Organically, MDWS has started to grow and therefore started offering a few more items in the area of reloading supplies and tools, lower half parts including triggers, some furniture items, etc.

Now that initial load development is over, and Wolverine barrels are in the hands of shooters, have there been any surprises? What are your impressions of its performance so far? How have results with the production barrels (ARP) matched up to the testing with the pre-production (PacNor) test barrel?

I am quite satisfied, excited even, with the .277 Wolverine’s performance.  It has exceeded my expectations and those of most shooters.  Testing is fun; you have the barrel you have, and the powders and other components that you can get at the time, and go “figure it out”.  Thankfully, I had a lot of help there too.  A very good friend of mine who can shoot off of his back porch agreed to do the initial load development and cartridge testing for me – thanks, Wade!.  I currently live in a Chicago suburb, and it just doesn’t lend itself as a proper venue for cartridge testing.  The test barrel was accurate, and so are the production barrels.  They behave differently as far as pressure and velocity results go, but it was to be expected as the test barrel was from a different manufacturer and had a different rifling profile.  Our production barrels are all currently utilizing 5R or 5-groove rifling, which seems to be ideal.

Where are you headed with the Wolverine in the near future? What long term goals do you have for it? What have you learned during this process that you didn’t anticipate.

I feel the possibilities for the .277 Wolverine are endless.  I truly feel it is the best all-around cartridge for the standard, 5.56 NATO AR15 platform using all standard parts, except the barrel, including all standard 5.56 mags without any modification needed.  The .277 Wolverine would make an excellent self-defense and CQB/Mid-Range combat cartridge.  It uses .277 bullets effectively, ranging from 80 to 110 grains.  It’s an excellent hunting cartridge for medium/large game out to 300 yards, and small game even further out.  It uses abundant 5.56 brass as a parent case and has many options in powders and projectiles.  Being built this month is a lightweight “youth” bolt action rifle in .277 Wolverine.  I’m really looking forward to seeing the results from that project.  For the recoil sensitive hunter, it just may be an ideal solution.


I’ve arranged for sized and ready to load brass to be available to the public with loaded ammunition coming soon.  As the  of shooters grows, so will its traction.  It’s only a matter of time before some of the large rifle and ammunition manufacturers take notice.


What I’ve learned from this project is that the learning never stops, and if you are passionate about something do whatever it takes to see it through – it doesn’t happen overnight.


Note:  Since this was written, two companies have come online with formed, ready to load brass, and factory loaded ammunition.  Mark has also started a Wolverine Forum for all things Wolverine at  The future for the Wolverine is wide open!



Loading Table



Caution:  Use of this load data is at your own risk.  All reasonable care has been taken to ensure it is safe, but we have no control over how it is used.  Not responsible for typos or printing errors.


The Wolverine is a bit different than other wildcats.  It is based on a case which has only about 25 grains powder capacity, and it has high expansion ratio, so the powders that work best are on the faster side of the medium burning rates.  It is an extremely efficient cartridge, so when you get to the top of the pressure ladder working up loads, it lets you know without any hesitation.

The best powders, with a couple of exceptions, are ball type.  AA-2200, AA-1680, and 1200-R are probably the best and cover the range of bullet weights easily.  One that has surprised everybody is AA-5744, which is an extruded type powder.  It is primarily used in many of the old black powder rounds because of its bulky nature, but it has turned in some very high velocities with 90 grain bullets particularly.

220072As with most AR calibers, pressure signs consist of flattened primers, swipes, ejector hole marks, sometimes pierced primers, and stretched primer pockets.  Because of the nature of gas guns, all of those except for stretched primer pockets can also be caused by timing issues such as over-gassing, or by headspace* issues resulting from improper sizing.  Knowing the difference is particularly important for anyone loading a wildcat.

A couple of things that you can use as a quick check for the mechanical side of things will help you decide whether its a pressure issue or a hardware issue.  If the rounds are ejecting at approximately 3 o’clock to 4 o’clock consistently, your gas port is OK and thus timing is good.  If the ejection pattern is more toward 1 o’clock, you are over-gassed due to either an oversize port or a carbine gas system.  The easiest fix is to install an adjustable gas block.  If cases are ejecting past 4 o’clock and the bolt doesn’t lock back on an empty mag or doesn’t pick a round from the mag, you are low on gas pressure and probably short stroking.  So, keep an eye on things as you proceed before you start trying to work up to the high end performance loads.

Keep good records of your test loads, and use a chronograph to track everything.  Some combinations won’t show pressure until you go over the line.  Watching the chronograph numbers helps by letting you know when velocity starts to level off, but primer pockets are the secret here.  When you seat a new primer, pay close attention to the force needed to seat it.  When pockets start to expand, it is readily apparent especially using a hand priming tool.  If pockets start to expand, back off at least half a grain below the charge causing the expansion, and call that your ‘max safe charge’.  Throw away any cases that start to exhibit stretching.

5744 does an outstanding job with 90 grain, but AA-2200 seems to be the best overall for all weights.  It is predictable, and superbly accurate.  The use of mag primers is highly recommended, and nearly all loads were developed with either CCI-41, or CCI-450 primers.


* Headspace in this context refers to cartridge fit in the chamber.  Nominal shoulder set back on sizing is .003” based on fired case dimension, measured from base to shoulder datum line.


 For load data provided by the Author, click here: .277 Wolverine Data