Before I begin, I just wanted to say that I originally wrote this guide in an article format for another purpose (which obviously didn't pan out). I hated to see the information contained within go to waste, so here it is. Enjoy!

MK13 Mod 5: A Holy Grail of American Service Weapon Clones

What do you mean by “Clone”?
    Gun owners who attempt to replicate military service weapons (or “cloners”, as we’re often called) are an odd bunch. We are simultaneously the most nit-picky enthusiasts in the firearms world while also being the most lax when it comes to our personal builds. The most hardcore cloner will reject a perfectly functional part if so much as the serial number range isn’t correct; but many of us also won’t think twice about molesting a $3,000+ weapon with Rustoleum spray paint bought from Wal-Mart. Many cloners (myself included) got addicted to the hobby the first time they felt the satisfaction of completing a tedious, expensive, and (most important of all) authentic service rifle clone. Unfortunately, this feeling is usually followed by a sense of emptiness that can only be filled by starting another build. I’ve been going through this wonderful/terrible cycle for the better part of 10 years and have had the pleasure of building several clones that were previously on my “bucket list”. The MK13 Mod 5 .300 Win Mag sniper rifle is (or rather, was) at the top of said list.


My personal MK13 Mod 5 clone, complete with a Knight’s Armament PVS-30 night vision clip-on device.

A brief history of the MK13
    When the U.S. Army announced a little over a decade ago that they were adopting the M2010 sniper rifle platform chambered in .300 Winchester Magnum to replace their existing inventory of M24 Sniper Weapon Systems (chambered in 7.62X51 NATO), the decision was touted as a leap forward in the capabilities of the modern marksman. Unbeknownst to many, the .300 Win Mag (with its approximately 50 percent greater effective range than 7.62X51 NATO) had already proven itself as an effective cartridge for military snipers within SOCOM for quite some time. The MK13 series of rifles (of which there are 8 total variants, or “Mods”) traces its lineage all the way back to the early 1990’s specifically with the M91A2; a custom-built, bolt action .300 Win Mag sniper rifle issued within the Navy’s SEAL teams. The extra energy and effective range afforded by the .300 Win Mag over the 7.62X51 NATO was an immediate hit among SEAL snipers, so further developments of the concept eventually led to a standardized and more widely-issued rifle and ammunition which were dubbed the MK13 (Mark 13) Sniper Rifle and the MK248 Mod 0 cartridge.


M2010 Sniper Rifle, chambered for the same .300 Win Mag cartridge as the MK13.

    It can be hard to differentiate all of the variants of the MK13, especially considering that some versions only differ in whether they are built for left-handed or right-handed shooters. The first MK13 variants were relatively “old-school” (at least compared to today’s bolt guns), utilizing a bedded McMillan A2 fiberglass stock and a Remington long action receiver. Later variants of the MK13 instead use a more modern “chassis” system from Accuracy International, which required much less time to properly install onto an action when compared to the older McMillan stocks. This saved a lot of time for armorers at Naval Surface Warfare Center-Crane (whom assemble the majority of MK13 rifles as well as several other weapon systems used by SOCOM), and even more time would be saved on later iterations of the MK13 with the addition of a Stiller action. Unlike an assembly-line Remington action, the Stiller actions did not need to be blueprinted (“trued”) and came standard with an M16 extractor mod (an upgrade that Crane armorers previously had to do themselves to ensure reliable extraction of empty shell casings). These time-savers were crucial when the demand for these rifles by operators within SOCOM increased from a few dozen builds per year to hundreds (or even thousands) per year.


A couple of MK13 Mod 3's built for the film American Sniper.

How to build a MK13 Mod 5
    With the history lesson out of the way I’ll show you readers step-by-step how to build your very own clone of a MK13 Mod 5, as well as the parts you’ll need in order to make it “clone correct”. It’s important to have a thorough understanding of the time, effort and -arguably most important- money that you will likely sink into building a MK13 prior to embarking on this journey. Many of the parts needed are very rare; this is due to the manufacturer only producing small batches once or twice per year (looking at you, Knight’s Armament…) or due to being discontinued altogether. There is no single source where you can pick up all (or even most) of these parts, so get ready to add scouring forums, auction sites, and buy/sell/trade pages to your daily routine. Not only are these parts difficult to source, they will demand a premium when you do come across them. As a final cautionary tale to readers, I want to stress that you should build a MK13 for the right reasons. It sounds silly, but the last impression that I want to give you is that the MK13 Mod 5 is some kind of “miracle” platform in terms of performance and quality. While a properly-built MK13 can be impressively accurate, they do not typically match the levels of accuracy brought to the table by something like a complete rifle from Accuracy International. It is also worth mentioning that the MK13 is a heavy, ruggedized service weapon... not a lightweight competition rifle. With a loaded magazine the MK13 Mod 5 tips the scales at just over 20 pounds. So, to rephrase, do not invest into one of these builds unless you truly have a passion for cloning and/or an appreciation for historical military firearms used in the Global War on Terror. Warnings aside I have broken down all of the major components you will need in the following paragraphs.


A MARSOC Marine firing a MK13 Mod 5 from a tripod.

AICS 2.0 Chassis: The heart of the MK13 Mod 5
    The first major hurdle in this build will be the most visually distinct component of the rifle; the AICS 2.0 chassis manufactured by Accuracy International. The particular version of this chassis used on military-issue rifles has been discontinued for several years now, and supplies have virtually dried up on the commercial market. Additionally, there are two different “versions” of the AICS 2.0 and only the “early version” with the PB (Pale Brown) color is correct. For the past couple of years a company known as Thoroughbred Armament was able to snag several surplus MK13 parts kits which were sold commercially. These kits were a cloners wet dream, since not only did they included many hard-to-find parts for the MK13 but were derived from real MK13 rifles, and as a result often had genuine wear-and-tear from use during deployments (can you really call it a “clone” if you’re using parts from the real thing?). Sadly, these kits have seemingly dried up as well… though that doesn’t mean you shouldn’t check out Thoroughbred Armament anyway! Along with the possibility that they might come across more of these kits in the future, they are a treasure trove of clone parts/accessories and are well-liked across the clone community.


AICS 2.0 Chassis. Note that this chassis is green, while the correct chassis for a MK13 Mod 5 is Pale Brown (similar to FDE). Fun fact, the green chassis is correct for the MK13 Mod 2 used by Army Rangers!

Action
    As I touched on already, those wanting to build a MK13 Mod 5 have the choice of two different long action receivers to use for their build. While early versions of the MK13 Mod 5 use the same Remington 700 long action receiver as previous variants (Mod 0-4), later versions were “upgraded” to the aforementioned Stiller MK13 action. While either action is “clone correct”, it is worth mentioning a couple of things; first, the Remington action will require more work by your builder to make it a “true” MK13 action (i.e. blueprinting, M16 extractor mod, etc) compared to the Stiller (which is virtually ready-to-go out of the box). Second, the configuration of the rifle also changes slightly depending on which action is chosen. Older Remington MK13’s featured a Remington MARS 20MOA scope rail (sometimes called the “diving board” rail), while rifles fitted with Stiller actions were instead paired with a Badger Ordnance IMUNS night vision rail. While there were a small number of issued rifles that used the older Remington receiver and the newer Badger IMUNS, most issued MK13’s either fell into the Remington/MARS configuration or the Stiller/IMUNS configuration.


Stiller's MK13 Action.

Barrel
    The barrels used on all variants of the MK13 are manufactured by Lilja, Inc. located in Plains, Montana. This is often the easiest part to source for a MK13 build as these are still in production and can be custom ordered with whichever profile is needed (including the “Mod 5” profile). Keep in mind, however, that Lilja (like most precision barrel manufacturers) sells these as barrel “blanks”. This means that, prior to your builder working his magic, you will simply have a steel tube featuring a .30 caliber hole with 1:10 twist rifling. In other words, your barrel will lack a chamber, threads for your receiver, as well as the cuts needed to mount the correct suppressor.


A MARSOC Marine fires a MK13 Mod 5. Note the odd profile on the muzzle end of the barrel designed to accommodate the KAC MK11 suppressor, as well as the barrel’s bead-blasted stainless steel finish.

Suppressor
    The MK13 Mod 5 is one of a few variants of the MK13 that uses (or in SOCOM’s case, re-uses) the Knight’s Armament MK11/SR25 Suppressor. While primarily issued with the Knight’s Armament MK11 (which is a semi-automatic sniper system), the MK11 suppressor is also one of the most recognizable features of the MK13 Mod 5. In past years these suppressors have been available periodically through KAC dealers, though they are much more scarce at the time I’m writing this and often sell for well above MSRP on places like Gunbroker. There is a silver lining however; while there are several forum threads around the internet claiming that you must send in your MK11 suppressor with the rest of your MK13 parts in order to be “fit” to the barrel, this is not entirely true. While some builders may require having your suppressor in hand when assembling your rifle, several others (such as the one I will recommend later in the article) do not, meaning that you can buy the suppressor first and then tackle the rest of your build while you wait for your Form 4 to be approved.


Knight’s Armament MK11/SR25 Suppressor.

Optics
    There have been several different optics seen in use on issued MK13 Mod 5 rifles, including some that were unit-level purchases or even personal purchases by end users. In order to simplify things I’m only going to discuss the most prevalent scopes used within SOCOM. Your choice of scope will likely be reliant on budget, availability, and/ or the desire to clone a MK13 used by a specific group within SOCOM. For example, the cheapest scopes that are clone-correct for the MK13 Mod 5 are from the Nightforce NXS series, specifically the NXS 3.5-15X50 (used frequently by Army Special Forces) as well as the NXS 5.5-22X56 (used frequently by SEALS and MARSOC). While these scopes are commercially available and relatively “cheap” (at least compared to other options I’ll discuss), you’ll get extra brownie points if you track down the more rare and costly versions of these scopes with the corresponding “Army-Spec” or “Nav-Spec” markings. While these markings only indicate that the scope features a certain reticle/turret combination that was specified by each branch, these would be “more correct” than a commercial Nightforce scope. All issued versions of the NXS scope would be mounted using 30mm Nightforce Ultralite Rings, with the ring height being dependent on which scope rail is being used with the ultimate goal of bringing the scope in-line with night vision and thermal clip-on devices.


A MARSOC Marine with a Nightforce NXS 5.5-22X56 riflescope mounted to his MK13.

    The next most common optic used on the MK13 Mod 5 was actually procured by SOCOM for a program entirely separate from the MK13’s. The PSR (Precision Sniper Rifle) solicitation awarded a contract in 2013 to Remington’s Modular Sniper Rifle (or MSR, later dubbed the MK21) and Schmidt and Bender’s PMII 5-25X56 Riflescope. Due to several largely bureaucratic factors, however, only the PSR optics (not the rifles themselves) were purchased in large numbers by SOCOM. These scopes were instead used on other sniper rifles in SOCOM’s inventory including the MK13. While a model that is similar to the PSR scope is available commercially, the military-exclusive version (like the aforementioned Nightforce NXS models) is “more correct”. The mil-exclusive version features a Tremor2 reticle, an FDE finish, as well as proprietary markings that are engraved on the scope body itself. The PSR scopes were mounted to MK13 Mod 5’s primarily using Larue 34mm LT111 OBR mounts, as well as with 34mm AWP Gen 1 PSR Rings manufactured by Operational Products Supply.


Issued MK13 Mod 5 with a Schmidt and Bender PSR Scope mounted.

Finishing Touches
    In this final section I’ll discuss a few smaller parts you’ll need for your build that weren’t expansive or complicated enough to warrant their own section. Bear with me, we’re almost done! Let’s start with triggers. Simply put, Remington receivers would be paired with Remington Walker triggers while Stiller receivers would be paired with an XTSP Model 22 Two-Stage adjustable trigger. As far as bipods are concerned, the most common by far is the tried-and-true Harris S-BRM with notched 6-9’’ adjustable legs. The final part that I’ll discuss is the recoil lug. While Remington and Stiller actions both typically come with their own recoil lugs, the “correct” lug was made in-house at Crane and features an L-shape design. While this specific recoil lug is not available commercially, there’s no need to fret. This actually provides me with a perfect transition to talk about reputable builders to send your MK13 project(s) to.


The business end of my MK13 Mod 5 clone.

I’ve got all of the parts, what now?
    While there are many competent gunsmiths that are familiar with assembling Remington 700-pattern rifles, few are familiar with all of the intricate (albeit, nit-picky) details that go into building an authentic MK13 clone. In fact there is only one builder that I personally know of that is deeply familiar with this specific platform, and that is Chris Higgins, owner of Red Bull Armory, LLC in Mitchell, Indiana. Between Chris’s Naval service as a SEAL sniper and his later career spent building service weapons (like the MK13) at Crane, he is able to give a unique and detailed perspective on the weapon’s history and design; making him the perfect individual to satisfy a cloner’s obsessive standards. Everything from the proof marks that Chris stamps on the barrel to the annotated logbook that he includes with every build makes it obvious that Chris knows exactly how to make a clone indistinguishable from the real thing. Along with using the correct taper to allow the MK11 suppressor to fit snugly onto the barrel of the MK13 Mod 5 (without ever needing to have your suppressor in-hand), Red Bull Armory also offers a recoil lug which is made in-house that is an exact replica of the one made by Crane. Red Bull Armory even sells MK13 parts from time to time, so be sure to check with them before you start searching!


Navy SEAL with his issued MK13 Mod 5. Notice that this rifle is an updated version with a Stiller action and Badger Ordnance IMUNS night vision rail.

Final Notes
    Whether I’ve talked you into, or out of, building a MK13 of your own hopefully I have at least shed some light on what to expect along the way. Needless to say these builds are not for the faint of heart, but the satisfaction felt when finally completing a project such as this is second only to pulling the trigger on it for the first time. From beginning to end, my rifle took about a year and a half to complete; which isn’t bad for a 100% clone correct MK13 project (the kit from Thoroughbred Armament sped up my build considerably). I’ll finish up by answering a question that I’m sure many of you are now asking: how does it shoot? Contrary to popular belief, cloners such as myself do occasionally venture to the range to shoot their clones (as opposed to just staring at them whilst sitting in Mother’s basement). Arguably true jokes aside, my first few range sessions with my MK13 Mod 5 have given me a metaphorical high that I haven’t felt since my very first time shooting a firearm many years ago. When using loads comparable to the military’s MK248 Mod 0 ammunition I am consistently shooting 0.5-0.7MOA groups, well within SOCOM’s (rather lax) 1-MOA requirement for the MK13. The recoil of the rifle is extremely subdued compared to the typical amount generated by a .300 Win Mag, which can be attributed to the rifle’s considerable heft. In all, the MK13 is an extremely easy rifle to shoot accurately and constantly leaves me wanting to fire just one more shot; which wouldn’t be a problem if not for the price of match-quality .300 Win Mag ammunition... speaking of cost, I purposely chose to leave out specific numbers on what a build like this will run. While I can assure you that building a MK13 is never going to be cheap, there is a lot of potential for cutting costs depending on exactly which version of the rifle you choose to build, as well as how patient you are in collecting the parts. With all of that being said, I wouldn't let a high price tag discourage anyone with a little bit of patience and diligence from going on this journey; because the end result is a rifle that not only looks great, but in itself is a piece of history that will retain its value and intrigue forever.

Nice post op.

I have wanted one since I got a chance to shoot one in Afghanistan.

Maybe it’s time to start part shopping.

The best time to start is yesterday

Had mine built by Jason from Accurate Ordnance. Waiting for the can to shoot it. Form 4 was sent in August of last year so maybe soon....

Any word on the mk248 mod 0 with the long OAL on gunbroker?

Very cool write up!

I bought a case, haven’t gotten a chance to try it yet though. The rounds are significantly longer than factory Federal GMM 190gr, but still fits in AI magazines without issue

The issue isn't with the mags, the issue is with the chamber. The Mk13 Mod 7 specifically has a chamber for the 220gr bullet (Mk248 Mod 1 ammo) and it's longer bullet that the 190gr (Mk248 Mod 0 ammo), which creates a longer OAL length. The new chamber reamer pushes the throat out more so that the 220gr bullet doesn't get jammed in the barrel's lands/grooves. I'm not buying any of that ammo because of this and if I did buy some, I'd run it through some properly set seating dies and seat the bullet to the proper depth for the Mk248 Mod 0 (if it is indeed seated long and that's what's causing the OAL issue).

If the bullet is seated further out, they could have mistakenly run the 190gr Mod 0 ammo through loaders set up for the 220gr ammo, this is the only thing I can think of for why it's a longer OAL. And if they were running the 190gr Mod 0 ammo to the 220gr Mod 1 specs, there might also be an issue with more powder (IIRC the Mod 1 has more powder that the Mod 0 ammo, about 77gr vs about 74gr). Don't use this load estimation, go look up the actual load specs. If there is more powder than normal in these Mk248 Mod 0 rounds, you'll have to reduce the powder load before you reseat the bullet to the correct depth.

Remember, it's always been recommended that you fire the Mk248 Mod 1 ammo in a rifle like the Mod 7 because it has the specific Mod 1 chamber. Mk248 Mod 1 ammo is loaded very hot and long (giggity), so if you put it in a regular Mk13 Mod 0/1/2/3/5 chamber, this might cause a serious issue with pressure spiking to dangerous levels.

This longer OAL Mk248 Mod 0 ammo might not be loaded as hot as Mk248 Mod 1 ammo, but the longer seating depth could jam it in the barrels lands/grooves, which could also spike the pressure. Like I said before, there could also be an issue with the powder load, not just the OAL. The Mk248 Mod 0 chamber is only for Mod 0 ammo and it's a very specific OAL. It's not designed for Mk248 Mod 1 OAL lengths, if this is the case with this ammo.

I have no idea if any of the above is what's going on with the newly released batches of long OAL Mk248 Mod 0 ammo, but use your best judgment. Unless you want to be nicknamed "lefty" for the rest of your life, you should put in a lot more research than "but still fits in AI magazines without issue." This goes for everyone who reads this, you've been warned. No matter what, always check your rifle and fires brass for signs of over pressure. If you see anything that points to it being over pressure, stop shooting the ammo immediately.

TL/DR:
Mk248 Mod 0 ammo could be loaded to Mk248 Mod 1 specs, just with a 190gr bullet instead of a 220gr bullet. This can lead to pressure issues in all .300 win mag rifles that don't have a specific Mk248 Mod 1 chamber. The silver lining is that this ammo might work just fine in Mk13 Mod 7 clones or other rifles that had the chamber cut with a specific Mk248 Mod 1 reamer.

I hope this all makes sense, I'm just trying to think of what could be going on. I just did a Google search for Mk248 ammo and came across this post. There are plenty of other people who have run into similar issues. Make sure you know exactly what's going on before you pull the trigger!

https://www.sniperforums.com/threads/military-mk248-mod1-psa-warning.35165/

Thanks for the reply, it makes total sense.  I figured I would pull some bullets, check powder / bullet weight, etc, and then if everything checks out with those rounds I could just seat all them to the proper OAL.

That's the perfect thing to do. If you can, please post your findings with the OAL and powder weight in this thread. If they loaded the 190gr bullet to 220gr specs, maybe they also put the wrong amount of powder in the case. That would be a pretty bad situation, since the Mod 1 ammo is a compressed load that tries to replicate the low end performance of the .338 Lapua Magnum. If the long Mk248 Mod 0 ammo is indeed produced to the Mk248 Mod 1 specs, you'll have to drop about 3 grains of powder (about 77gr to 77gr) before reseating the bullet to the proper depth. My grain weight is just a guess, you'll have to look up the specifics on the load.

These aren't things to be taken lightly and the information you post will be extremely useful to everyone here. You'll be doing a lot to keep things safe and your help is greatly appreciated. I hope everyone knows how to looks for over pressure signs if they decide to use this ammo as is.

Thanks for the info, I’ve been hesitant to shoot this new ammo for pretty much these exact reasons. However, I have conferred with Chris at Red Bull Armory and based on the OAL of the “seconds” he thinks it will be safe to shoot (at least in one of his rifles, which he states uses the same reamer/chambering on the Mod 5/7). I have also talked to other individuals who have used the same “seconds” ammo with the same “exceeds Sam spec” warning sticker and haven’t encountered one that has had issues thus far. I will try to chronograph this ammo in the next week or so and compare it to my factory Federal GMM 190gr (which chrono’s around 3050fps out of my MK13). Assuming the velocity isn’t crazy high I believe it will be alright to shoot through a properly built MK13.

Just keeping the thread alive...



Haven't been this excited for a stamp in a long time. Purchase date was 6/15/21.

ETA quick mock up. My local gunsmith wanted the can when he finishes the barrel profiling so its not done yet.

Looks great! I have a feeling that all of the MK13 builds we’ve been seeing lately are gonna slow waaaaaaay down with the chassis and MK11 suppressors drying up once again. Sad, but it was bound to happen eventually