It really doesn’t matter the reasoning behind building a precision AR10-style rifle, because it’s typically a justifiable pursuit.
Ready for the capabilities of a precision .308-platform semi-auto? It’s a relatively easy task to assemble precision parts.
After conversations with several LE snipers over the years, I learned they value a short-barreled .308 for at least two reasons. First, hide sites are often improvised in tight quarters. On several occasions, the confines of a parked automobile provided the only available cover, and a carbine-length rig worked much better than a long-barreled rifle.
Secondly, many LE agencies specify very specific loads for sniper work, such as Federal’s Gold Medal Match .308 loads tipped with 168-grain SMKs. Since the average range of engagement is well under 200 yards in urban settings, a sniper doesn’t give up much by shooting a rifle with a 16-inch barrel compared to a rifle equipped with a barrel that may be 10 inches longer.
When I first got the assignment to test and evaluate MEGA Arms MATEN monolithic upper .308 rifle, the assignment took a left turn and wound up here. Instead of testing complete rifle, I wound up acquiring a MEGA Arms matched lower and upper receiver for this article. That left me with the opportunity to assemble various quality parts and build what I consider an ideal self-loading .308 for counter-sniper operations.
Taking a closer look at the MEGA foundation for this rifle build reveals a sturdy 7075-T6 aluminum billet that’s milled with distinctive lines. The upper and lower receivers and handguard feel quite sturdy, with their combined weight of 42 ounces disassembled.
Of note, the MATEN upper and lower receivers accept a wide variety of .308 components. Included in this new platform are an upper receiver, lower receiver, billet charging handle, threaded bolt catch pin, take down pins, dust cover door and upper receiver tensioning screw.
When assembled, the upper and lower receivers lock up tight as a vault, thanks to close manufacturing tolerances and the tensioning screw.
MEGA’s billet upper and lower have been designed to be the most versatile and compatible platform available, which is evidenced by the wide variety of other manufacturers’ components that fit this receiver set. The MATEN comes standard with laser engraved “T” numbers.
An integrated trigger guard adds functionality and strength, and the included billet charging handle features an anti-slip surface for improved grip.
As previously mentioned, the MATEN’s capability is an AR builder’s dream. Designed to accept any AR-style .308 barrels and bolts, which means you can use your AR10/Noveske or SR25/DPMS components. MEGA Arms recommends using the same manufacture for your barrel and bolt, and they suggest that “always assembly should be done by a qualified gunsmith, using the proper head spacing gages.”
Once MEGA Arms changed their initial direction with building a monolithic upper receiver, their engineers got busy designing an alternative. The upper receiver is machined to accept their lightweight aluminum handguard. The handguard’s attachment and fit to the upper receiver is via an octagonal male/female orientation. Once the upper and handguard are assembled, 12 screws tightly attach the two units rigidly together.
The Build
My parts list for the MATEN build leaned heavily toward JP Enterprises components. A JP Supermatch barrel chambered in .308 got the nod. The medium contour 416R stainless barrel measures 16 inches, and is rifled with a 1:10 twist rate.
Some of the attributes of this premium barrel is that it is lead lapped, air-gauged and cryogenically treated for cold bore shot predictability, minimal thermal drift, extended barrel life and excellent accuracy.
A JP Enhanced Bolt was individually headspaced to the barrel and included as a set. The barrel’s contour measures 0.750 under the gas block and 0.875 inch forward to the 5/8-24 TPI threaded muzzle.
The first step is to apply a thin coat of lithium grease on the barrel where it slides into the upper receiver, carefully assuring that the barrel’s alignment pin indexes into the receiver’s alignment slot.
More lithium grease was applied to the MATEN’s barrel nut to keep it from galling when tightened. I attached the supplied MEGA Arms barrel nut wrench to a ½-inch torque wrench and set it to 65-foot-pounds of torque. The nut was tightened, loosened and then retightened, per specifications.
The next step in the assembly was to install the gas block and center it with the supplied marking screw. This left a faint mark on the barrel used as an index point. I placed the barrel in a vise block and used a drill press to drill a slight dimple.
When the gas block was replaced the final set screw was used to help lock the part in place. The rifle-length gas system is managed with a JPE JPGS-8 low-profile adjustable gas block.
I picked a red JPE Thermal Dissipator to match my taste. The only thing left to do was install the MATEN handguard. A short KeyMod rail on the bottom forward end accommodates a bipod.
In keeping with the other JP parts, I selected a LMOS bolt carrier group and a Silent Captured Spring. JPE’s .308 LMOS (Low Mass Operating System) is a departure from AR-10-type bolt carrier assemblies.
The LMOS bolt carrier group weighs 14.7 ounces compared to an AR-10’s bolt that weighs 19.4. That’s a 24 percent reduction. Counteracting the lighter bolt assembly is a heavier recoil spring in the Silent Captured Spring. The benefit of the spring set is that it eliminates the characteristic “twang” when you pull the trigger.
Next on the agenda was stock selection, so I installed a Mil-Spec rifle-length receiver extension. To that, I attached a Magpul PRS (Precision Rifle/Sniper) adjustable stock. It’s designed for the longer charging handle throw of 7.62 NATO platforms.
The Magpul stock offers a customized feel of a precision target stock. The PRS adjusts for both comb height and length-of-pull.
Compared to the A2 stock, the PRS can shorten LOP by ¼-inch or extend it by ¾-inch. It also provides a ¾-inch of comb height adjustment. Machined aluminum adjustment knobs feature positive-locking click detents to maintain position. It’s under recoil and allows easy, tool-less adjustments.
The PRS’s aluminum butt-plate and alloy steel adjustment shafts provide stability and strength to withstand severe impact conditions. Rubber butt-pad offers positive shoulder purchase to prevent slippage for optimal accuracy even with body armor or modular gear. A bottom Picatinny-type rail allows for monopod use, and I attached an Accu-Shot monopod to match an Atlas BT10 bipod on the handguard.
The supplied single-stage Mega Tactical Trigger offers adjustments to minimize over-travel and trigger creep. It features a widened leading edge for comfort, and an appealing structural appearance. It brakes at a clean 4 ½ pounds.
Range Time
Even though accurate and effective, I chose not to install a JP compensator on this rifle. Instead, I opted to either shoot this rifle without a comp or screw on an Advanced Armament Corporation Cyclone suppressor.
At the range this rig provides a quieter experience, and occasional shots without hearing protection, shooting without a compensator would save my hearing. A proper optic was only befitting, so I mounted a Night Force NXS 5.5-22x Zero Stop scope with a Mil Dot reticle.
To put the MEGA/JP .308 build through its paces, I selected five factory loads. An Oehler 35P chronograph collected velocity data. I loaded up a Magpul 20-round PMAG magazine and got started.
The MEGA Arms rifle is compatible with any SR25/DPMS-type magazine such as the previously mentioned PMAG, Knight, CMMG and C Products magazines.
After zeroing the Night Force optic and adjusting the JP gas system to lock open on an empty magazine, I loaded a magazine with Federal’s 175-grain Gold Medal Match. Checking the group through my scope after I fired the first three rounds led me to believe that my scope rings were loose and I was missing the target. I checked the mount and everything was tight. I sent two more rounds down range, got up and walked to my 100-yard target to try and find my stray shots. What I found was a tight 0.275-inch five-shot group. Subsequent groups were larger, but not by much. Federal’s Gold Medal Match 168-grainers produced a 0.663-inch best group.
Hornady’s Superformance 168-grain match loads flew almost 150 fps faster than the Federal load of the same bullet weight, and they stayed sub-MOA. Winchester’s 168-grain match loads splint the difference in velocity, and were just over MOA, with a 1.072-inch group as its best.
The last factory load tried was from a new ammunition company, Australian Outback. Their 168-grain Sierra Match Kings load averaged 2,561 fps. It hovered around MOA, with a 0.945-inch group as its best.
Tallied together, the parts for this rifle build come to about $2,000. That’s a serious investment for anyone, but a bargain for a high-performance .308 semi-auto that’s a tack driver. The Mega MATEN is a solid foundation for any rifle build. Put the right parts together it produces one of the best shooting rifles you can wrap your hands around.
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