One of the coolest things about the Modern Sporting Rifle (MSR), built on the well-known AR-15 platform originally designed by Eugene Stoner, is the fact that the system is largely modular and can be assembled and modified by anyone possessing some basic tools and a bit of mechanical aptitude. Happily, for firearms enthusiasts, “easy to assemble” also translates to “easily customizable”. The concept has been so successful that the AR-15 and its countless variants have earned the names, The Swiss army knife of guns, frankengun, LEGOS for adults and others.
Assuming all the individual parts are within specification, a builder only needs to verify chamber headspace and mechanical function before heading to the range with their completed rifle. Of course, that doesn’t mean the gun will be “a shooter,” as considerable experience and skill are required to build a highly accurate rifle. Generally, however, a frankengun will usually perform safely and reliably, even if the builder doesn’t possess major gunsmithing chops.
You can’t go wrong basing your ‘Ultimate” MSR build on a set of KSP Gen 2 Polymer upper and lower receivers.
For these reasons, every hardcore firearms enthusiast eventually considers buying, building or modifying their own “ultimate” MSR. The idea of having a personalized rifle is highly appealing, but it’s often a practical matter as well. What one shooter considers the supreme MSR might be nearly useless for someone else. A 3-gun competitor has far different needs than a special-forces operator. Similarly, someone teaching their spouse to use a rifle for home defense doesn’t have the same set of requirements as a police officer. Likewise, building a gun for coyote hunting at 500 yards is different than building a rifle to take out feral pigs at tag-you’re-it distances.
That’s why it’s smart to consider the intended purpose of the gun before everything else.
Robar choose a considerable number of Bravo Company parts on the PolymAR-15, including at KMR Alpha fore end.
Decisions can then be made regarding complete guns or individual components that best serve the guiding purpose. For example, a varmint hunter might prize accuracy above all, while a cop or soldier places reliability at the forefront. The more one can define the role and overall requirements of their pending build or purchase, the greater the rewards will be later.
Once the important concepts have been identified, it’s time to decide whether your wish list is available on a production gun, whether you’ll have a reputable builder assemble your custom or semi-custom rifle for you, or if you’ll start acquiring the necessary parts and complete the build yourself. The big problem isn’t finding information, opinions or the parts; enjoy the process, because there’s plenty out there. Rather, it’s winnowing down the overwhelming number of choices into something manageable.
The BCM Mod 5 charging handle used on the PolymAR-15 flies above a V7 Titanium castle nut. Also seen at left is the Magpul MBUS backup rear sight.
Our Needs
In my case, I place a high value on expertise and experience. I wanted a lightweight, reliable rifle with sub-MOA accuracy, but also wanted to learn as much as possible about putting one of these guns together to share with my readers.
Ultimately, I found that expertise at Robar Guns in Phoenix, Arizona, and opted to start with their PolymAR-15Ti – a solid example of a premium, commercially available rifle that is assembled using the finest quality parts from a variety of sources across the industry. Not only does this rifle meet my baseline needs with respect to weight and performance, the people who make it have decades of accumulated experience building these weapons, so their choices speak volumes for the home builder.
The end user of this gun, according to Robar CEO Freddy Blish, is the soldier, police officer or hunter who will hump the gun long distances and needs a rugged, totally reliable and highly accurate weapon. “The goal was to go light,” Blish says, “for situations where you might be carrying the gun for long periods of time. You know, ounces are pounds and pounds are pain!”
Blish also acknowledges a secondary market: “I don’t want to say that the PolymAR-15Ti was designed for smaller-statured people or women, but those customers have become a good audience for us because they love the light weight.”
Weighing in around 4.75 pounds, nearly two pounds less than the average MSR, the Robar gun comes with guaranteed sub-MOA accuracy with appropriate ammo.
Our Rifle
The PolymAR-15Ti is built around a Kaiser Shooting Products Gen 2 Polymer Upper and Lower receiver set, which is available in three colors. This new action housing has more 7076 hard-anodized aluminum reinforcement in the lower receiver and uses a new polymer composite that is five times stronger than steel for its weight. Blish and his highly experienced gunsmiths chose the KSP components not only for their weight, but also because their strength reduces flex during cycling, which greatly enhances reliability and accuracy. “Many of our customers need to trust their life to it (the PolymAr-15). We understand that and won’t compromise there,” Blish says gravely.
The weapon’s furniture comes from the Bravo Company Gunfighter series. Several other parts such as the charging handle, fore end, barrel nut and sling mount are also from Bravo. The Bravo fore end uses the KeyMod system and sports a BCM Model 3 vertical grip.
The barrel is a Faxon 1:8 5.56 NATO model mated to a V7 Weapons System titanium, low-profile gas block. Likewise, the titanium QD receiver end plate, castle nut, pivot pin, takedown pin, magazine catch, mag catch button, selector switch and flash hider are also from V7. You can also order a BattleComp 1.5 Ti flash hider.
The Robar Mil-Spec Bolt Carrier Group is custom manufactured from P6 steel (Carpenter 158) and sports their well-known proprietary NP3 surface treatment that combines Teflon with electroless nickel for an unbelievably durable, slick finish. The trigger assembly is an enhanced Robar Mil-Spec group coated in NP3.
FLIR’s compact ThermoSight PRO PTS233 thermal scope is lightweight and produces a wide, 12-degree FOV that’s ideal for close-to-medium-range applications in any lighting conditions.
Topping It Off
The flat top receiver on the PolymAR-15Ti comes standard with a MagPul MBUS backup front and rear folding sight set. On our test gun, however, we wanted to add daytime and nighttime targeting capability, while keeping an eye on overall weight. Ultimately, we chose the compact FLIR ThermoSight PRO PTS 233 thermal-imaging scope as the primary optic for our featherweight MSR.
The FLIR ThermoSight PRO PTS233 was an easy choice for several reasons, but primarily because it sets the bar in the current market for size, weight, power, and performance.
Weighing less than 24 ounces, the compact PTS233 is powered by the FLIR Boson thermal camera core, delivering smaller, lighter optics with increased image performance and range. The FLIR ThermoSight PRO PTS233 offers improved object detection and classification in the field and clean thermal imagery in any light—from low contrast daylight to total darkness—or through light smoke, haze or fog. Additionally, its 19mm-lens produces a 12-degree field-of-view (FOV), which is ideal for close- to medium-range applications. A 4X digital zoom delivers increased versatility and extended range. I also liked the fact that the PTS233 offers multiple thermal imaging palettes and shot-activated, onboard recording of still images and videos. And all of this comes for a price below $2,200—less than many would spend for a quality, day-only optic.
For those seeking additional range in a thermal scope, FLIR offers two other compact and lightweight models in their new ThermoSight PRO line: the 50mm PTS536 with a 4.5-degree FOV (1.65 lbs.) and the 100mm PTS736 with a 3-degree FOV (2.14 lbs.).
Tips for the Home Builder
For the would-be home builder, Blish says there are three key components to building a quality MSR: a good quality receiver set, bolt carrier group, and barrel. He also points out that the trigger group is another area where improvement can be especially valuable. “You really have to work to get a good barrel shooting well with a bad trigger, whereas a good trigger can really help with a less accurate barrel,” the retired Marine Lt. Col. notes.
Cost is often a major motivating factor for building an MSR, and while building a complete rifle at home can definitely save money, scrimping on parts is a fool’s errand. There’s usually a good reason why one component costs more than another. “You know,” Blish points out, “Pat (famed AR-15 expert, Pat Rogers) used to say, ‘buy once, cry once.’ He’s right. I value quality over price anytime.”
A custom rifle built on the AR-15 platform is certainly within reach of most shooting enthusiasts, should they decide to take the plunge. The only major downside is the fun and satisfaction involved. Yes, I said downside, because once the first rifle is completed, the urge to build another (and another) only grows exponentially. It’s an itch that can’t be ignored.
I recommend you scratch it.