AR15 DMR Build: Lessons Learned, Parts Reviewed.
What is a Designated Marksman Rifle?
“Designated Marksman Rifle” is a term that developed for rifles issued to particularly proficient shooters within a small infantry unit. These soldiers act as force multipliers by making precise or long distance shots that can impact the momentum of a firefight, but who retain the ability to perform ordinary infantry functions. Designated marksmen are not snipers. They are an integrated element of a fireteam designed to ensure that engagement of far away targets is possible. By necessity, DMRs are capable of engaging at both close and long range without sacrificing mobility.
In the civilian world, a DMR style rifle is a jack of all trades. If I could only own a single AR15 to use for all kinds of applications save home defense, a DMR build would be my first choice. The reasoning is simple: It’s accurate and fun to shoot at ranges between 25 and 400+ yards. Whether you’re hunting, three-gunning, or just plinking on your own property, a DMR build will likely perform to your needs. While we were building this rifle, we made a few mistakes, which we’ll pass on to you as lessons learned. First, we’ll take you through the build from the ground up.
Upper & Lower Receiver
This build started on Reddit’s Gun Deals page. If you are trying to save money for any reason, we advise you to stay away from that wonderful webpage. We found a very well priced, very attractive, tungsten grey cerakoted “builder kit” by Aero Precision. The kit came with a lower receiver, an upper receiver, and a 15″ quad rail. We wouldn’t realize until later what a problem that rail would become. As a general rule, a 15″ quad rail is fairly unnecessary. These days, you can easily save weight by using an M-LOK or Keymod system that allows you to simply attach rail space where you actually need it. Saving weight and adding comfort will be important elements of your DMR build.
Aero Precision M4E1 Enhanced Upper Receiver
This upper is convenient, but limiting. “Enhanced” refers to the fact that one can very easily install a handguard over a free-floated barrel. Barrel installation took just minutes with the included barrel nut and a torque wrench. Handguard installation took even less time- just slide your BAR/Aero handguard over the barrel and fasten eight screws. Notice how we said your “BAR/Aero handugard?” That’s the problem. By making the installation of a rail slightly easier, Aero has done two things: first, they ensured that your handguard has to be fat: slimmer handguards don’t seem to be available for this platform. Second, they limited your selection of handguards to only BAR-style products. BAR refers to the use of an integrated barrel nut on the upper receiver that allows for the handguard to be attached via screws. A limited number of manufacturers have produced BAR style handguards, including Spike’s Tactical and Seekins Precision. Should you want a BAR style handguard on your non-enhanced upper for some reason, Aero sells an adapter. The proposed advantages of superior alignment and fit of handguard to upper receiver don’t seem functional enough to justify limiting your handguard choices- we suggest avoiding an Aero upper for this reason alone. Other than the inconvenience of choice, the upper has performed flawlessly.
Aero Precision Lower Receiver
This is a fairly standard lower that functions as expected. There is a tensioning screw in the grip tang of this lower that allows the user to fit upper and lower together a bit more tightly via the nylon-tipped screw included. Other than that, the only notable feature is a very slightly flared magwell. Consider this a standard lower by most accounts. We feel comfortable recommending this lower if you can get one for a reasonable price: around $65 or so.
We used Seekins’ magazine release, bolt catch, and safety selector because we’re special princesses. They work fine. They’re slightly bulkier than standard parts, which makes them about one micron easier to operate.
We were excited to toss the 15″ Aero Quad Rail that came with the kit. When shooting unsupported, the sharp edges were uncomfortable, so we covered them with rail covers, which added weight to the rifle. Basically, we don’t see a good reason to use a big heavy cheese grater on the end of your already-weight-conscious rifle. We ordered the 15″ M-LOK offering from Aero, and we’re much more pleased. We had heard whispers of poor quality fitting on their handguards, but haven’t experienced it with either product that we’ve handled. The M-LOK Quantum weighs in at 13.81 oz, which is 1.23 oz lighter than the quad rail. Unfortunately, we could have saved even more weight by going with an option like Seekins’ NOXs, which weighs just 9.2oz. Again, we were limited by the “enhanced” upper, and although Seekins uses a “BAR” style mounting system, it has since changed and is proprietary, meaning that we couldn’t use the NOXs. Another complaint we developed around this handguard was the size- it has an internal diameter of 1.8″, which would be nice if it were intended to shroud a suppressor. As things stand, that’s not in the future for this build. We’ve found slimmer handguards to be more comfortable since playing with others that we’ve come across. We chose a 15″ option because of the stability it would provide with a forward mounted bipod. The further back a bipod is mounted, the more exaggerated the muzzle movement. This is a good rule of thumb for bipod builds, and not the result of too much Costa Ludus YouTube tactical armchairing.
Bolt & Bolt Carrier Group
No-name, bone-stock, run-of-the-mill, zero-special-about-it, boring-ass, vanilla, bargain-bin part. There are myriad bejeweled, TiN coated, or rabbinically blessed BCGs on the market, and none of them affect accuracy in a meaningful way. There’s some talk about bolt/barrel matched pairs potentially being useful in this regard, but we figured it best to spend the money where it matters: barrel, trigger, and …optics. We still haven’t gotten around to the higher end optics yet. Just a note: higher end bolt/BCG offerings can be neat. Coatings can make cleaning a breeze, slightly reduce recoil, and make your rifle look super slick- we just didn’t feel the need to spring for that on this build, although if we find an extra $200 in a pocket after a load of laundry…
If you’re looking for the capability to shoot MOA accuracy (or better), you’ll want to invest in a nice barrel. We opted for the 18″ Recon Tactical by Wilson Combat. It’s a fluted, stainless steel beast of a barrel that features a hand polished bore and hand polished feed ramps. We’re not sure that the hand polishing actually affects practical accuracy at all, but it sure sounds nice. With a 1/8 twist rate, it’s best suited for 62 or 77 grain projectiles. A quick note on twist rate: for every eight inches, the projectile will have rotated one full turn, thus the notation “1/8 twist rate.” This twist rate is commonly found on match-grade 18″ barrels, primarily because it’s a solid compromise that will reliably deliver middle-weight projectiles with better than average accuracy. 62/77 grain 5.56 are both common weights for match-grade ammunition. Barrel length is another factor: a longer barrel will add a bit of velocity, which can be helpful out around 300+ yards. The 18 inch barrel is the preference for may DMR builds because of the added velocity without the sacrifice of maneuverability. This barrel is fairly heavy, but impressively accurate. It is prone to rust, so we recommend coating it if possible. We did so with burnt bronze cerakote. Overall, Wilson puts out a consistently high quality product that we recommend if you’re feeling spendy.
TTAG’s Muzzle Device Tests are is an excellent resource for determining which muzzle device to choose for your rifle. (Part I, Part II) Keep in mind that these tests were done in 2014 and 2015, respectively- there have been plenty of newcomers to the market since then. We elected to choose the M4-72 Severe Duty Compensator by Precision Armament. This three-baffle comp has a large expansion chamber, vents gas back and up, and drastically reduces recoil. In TTAG’s second Muzzle Device Shootout, the M4-72 reduced recoil by 73.5%, and it won both contests. It’s definitely not something you want to stand near on the line, though. It’s comfortable enough for the shooter, but does not feel good if you’re an unsuspecting bystander. The weight of this rifle combined with the M4-72 conspires to create a very smooth shooting rifle that facilitates easy follow up shots from a supported position. This thing is loud and the shooter can definitely feel the gas, so it might not be ideal for a first build or for people who have problems with flinching. For folks who don’t mind noise and a little heat, it’s an impressive compensator that’s functional and effective.
We chose the SR-5 by Accu-Tac. This big badass hunk of billet is heavy (more on that later), but super stable and sturdy. The ratcheted legs are a top convenience element for the SR-5. All the user has to do to extend the legs is to tug at them gently. To retract them, just hit a lever and they pop back in. The SR-5 also has 180 degree spring loaded & cogged legs. In this case, “spring loaded” seems like a rather backward way to describe the leg angling and locking mechanism. The joint is a half cog, the slots of which allow for the leg to be locked into place once it is pulled away from the mechanism and angled into the next cog-slot. The spring puts pressure on the leg as it is pulled, so that when it is released, it easily snaps backwards into the cog-slot. This system allows the legs to be stowed either facing away from or into the rifle. The QD system works. The bipod attaches to a 1913 style rail, and the user simply hand-tightens a screw, then closes the lever. Over tighten, and the lever won’t close- under tighten, and it will close too easily. Simply apply Goldilocks style logic and it’s a set and forget kind of situation. The “feet” of the bipod can be swapped for spikes, which are useful in different kinds of terrain. Unfortunately, one of the first things we’re going to change about this rifle is weight dynamics. This bipod is simply too heavy for this build. With the heavy barrel and bulky items like the UBR, we’re going to have to find a few ways to shave weight, and the first thing we’ll do is try out an Atlas. Read our review here.
UBR! UBR! UBR! We love the Magpul UBR. It might not be ideal for this build, but it’s a fantastic design that we highly recommend. The UBR is composed of two primary pieces: one is a buffer tube for your rifle that’s coated in comfy polymer for your face bones. This means that if you’re planning a build that includes the UBR, don’t buy a buffer tube. The second piece of the UBR is a the “stock” element, which rides up and down the buffer tube when you switch positions/lengths. Fully collapsed, it looks like a solid stock. When you start to extend it, the two piece design becomes apparent. It’s a touch heavy, but it really does feel the most solid out of any stock I’ve used other than a standard A2. Part of the weight is intentional- Magpul’s intention was to offset the imbalanced weight rifles that are front-heavy because of rail accessories or heavier barrels. The counterbalance is nice, but when your rifle starts to get into the 12 or 13 lb range, (for most rifles) it’s time to start an AR15 diet. Unfortunately, we don’t recommend the UBR for DMR builds. There is no good way to get a cheek riser incorporated into this stock, and there isn’t one on the market. This is primarily because it would impede charging handle travel, but a PRS won’t. The PRS is fully adjustable, including length and cheek weld height, which makes it better suited for a DMR. The PRS is quarter of a pound heavier than the UBR, so you’ll need to take that into consideration when you’re selecting parts. The UBR still works on a DMR, it’s just not as easy to acquire a solid shooting position in a short amount of time because you can’t simply jam your face into your pre-adjusted cheek piece. It’s a minor gripe, but a gripe nonetheless.
We went with the CMC 3.5 lb Single Stage Flat Trigger. It was crazy simple to install, and fits snugly in this lower receiver. I’m a huge fan of flat triggers. I like their feel and look, and would run one in every gun I had if I could. When it comes down to it, it’s really just about personal preference. We suggest you try one out before you buy, as some people just won’t like them. The idea is that flat triggers make for a more consistent trigger pull and potentially lighten the “felt pull.” Frankly, the technical benefits of a flat trigger are so minuscule as to be irrelevant: if you like how it feels, use it. Here’s the issue: single stage triggers are not great for precision shooting. Again, this is also a matter of personal preference, but let me elaborate a bit. For newcomers, “single stage” might sound special. It’s not. Most pistols and rifles come stock with single stage triggers. Pull slowly… and bang. Trigger pull form affects accuracy greatly, as anyone who has experience with pistols know. A two stage trigger minimizes this (and other problems) by creating, well, two stages. The first stage leads to a “break wall,” which is basically an indicator that there’s just a tiny bit more pull left before the shot. This not only helps to minimize point of aim drift related to trigger pull, but lets you time your shot more effectively. Some triggers are non-adjustable, with something like a 2.5 lb first stage and a 2 lb second stage. We would have selected a two stage trigger over the CMC if we had watched this helpful video first.
Save your pennies, kids- this one’s important. Here’s a decent rule for precision shooting: be willing to spend at least 50% of the total cost of the rifle on the optic. We didn’t, although better glass is definitely on our shopping (wish) list. The Vortex Crossfire 3×9 is a perfectly decent scope, but it just doesn’t stack up to higher quality optics. The DMR must be able to engage targets at both close and long range, meaning that if you’re not running offset irons or a red dot along with a scope, it’s a good idea not to get a super high power piece of glass. 3x magnification should really be the bottom end, because it’s tough to engage and transition between targets at 25 yards at 6x. We recommend a higher end 3×9, or any high quality 1×6 optic if your eyes are good.
Why High Quality Optics?
If you’re a buy for life type, you already know part of the drill: durability. If you’re putting together a rifle that you may entrust with your life at some point, this element speaks for itself. If you’re like most of us and just like to shoot or hunt a lot, you may feel more comfortable with a lower cost optic that has an astronomically good warranty, like a Vortex. If you’ve ever looked through high quality glass like Nightforce, Trijicon, or Schmidt & Bender, you’ll know what I mean when I say that the sight picture looks better than real life. Light transmission, clarity, chromatic aberration (color fringes), less “fuzz.” The clarity and brightness of a high quality optic is extremely helpful at longer ranges. Another benefit is the consistency of adjustments and your zero. A good scope (affixed on good rings) will hold zero and respond reliably to adjustments. The Crossfire will do you just fine for paper punching at 100 yards, but we recommend saving up for something like the VX-R Patrol by Leupold. Don’t forget a decent set of rings or mount- they’re responsible for keeping the optic secure enough that you can drop it without affecting your zero. We chose a Burris P.E.P.R, which has been solid. It keeps the scope a touch high, but has done the job just fine.
Red Hatchet’s Lessons Learned:
- Remember to be weight conscious as you select parts.
- 2-Stage triggers are better for precision shooting.
- Save up for optics, they’re part of the rifle.
- Remember that BAR style uppers limit handguard selection.
- Consider a stock that features an adjustable cheek weld.
A note on the Cerakote:
We’re working on an article about the whole process. Our local gun shop gives us access to all kinds of neat stuff, and helped us do our barrel, trigger, and dust cover in burnt bronze. Stay tuned.