If you enjoy shooting common calibers such as .223/5.56 you most likely own or enjoy shooting AR-15 rifles. From competition to self defense there are countless reasons to love AR rifles. They are easy to use, can be configured in so many ways that it can make your head spin and they can be chambered in a number of popular rounds. However, if you are anything like me you eventually want more out of the gun than the small frame AR-15 calibers offer. An AR-15 can be chambered in a number of intermediate cartridges such as 6.8SPC, 6.5G, .300BLK and some others. Those cartridges are good, but they offer a limited amount of performance for shooting at distance or for hunting game at ranges longer than 250 yards. And let’s face it, the larger calibers offered by a .308 parent cartridge fit a larger need and ease of performance. Another issue is that building a .308 AR was difficult due to the lack of parts compatibility. This was something that Mega Arms decided to fix, and they developed the MATEN series of receivers.
The Mega Arms MATEN series of receivers will accept both Armalight and DPMS pattern barrel extensions, and will accept SR-25/DPMS pattern magazines. What this means is that you can use most any .308 pattern barrel so long as you use the same pattern bolt. (for example DPMS pattern barrel extensions require DPMS pattern bolts) On top of that, they simplified the lower by making it accept AR-15 lower parts which eased the issue of compatibility.
DPMS pattern rails can be used on the standard receiver sets and any buffer tube will work on the lower. Basically, Mega Arms took the simplicity of building an AR-15 and made it so you could do the same with the heavier .308 and similar rounds. For a little extra, Mega Arms released their MKM MATEN set. It comes with an upper receiver, ambidextrous partially stripped lower receiver, and a Key Mod rail. The rifle length set comes with a 12” rail and the Extended Rifle Length rail is 14”. What really sets the MKM apart is how the rail attaches to the upper. The upper receiver and rail attach to each other, but the rail does not touch the barrel or barrel nut. The rail attaches directly to the receiver and not to the barrel nut unlike most rails. This means the barrel is truly free floated! Last year I took an 18” LaRue Tactical 7.62 OBR hunting and to a major 3-gun match.
The gun is well made and hits were no issue, but the extra length while hunting suppressed and weight while shooting 3-gun prompted me to look for another option. Also, I started looking at the cost of buying another .308 AR and decided that I wanted to try and build one. At that time Mega had just announced the MKM series receivers would be released so I ordered one of the Extended Rifle sets. My goal was to have a shorter lighter .308 that would be capable from point blank to the effective range of a 16” .308. The overall length of the gun was to be shorter and the overall weight was to be lighter than my 18” gun.
I needed it to have soft recoil for fast follow up shots in competition and be able to at least shoot a 5 round group under 1” at 100yds. I considered a 14.5” barrel, but ultimately decided on a Rainier Arms Select 16” .308Win barrel. It has a 1:11 polygonal twist rate and mid-length gas ports. The barrel is not heavy and not light at 2.5lbs made from 416 stainless steel. I then chose a Syrac Ordnance adjustable gas block. Syrac Ordnance blocks adjust like most do with a set screw, but the screw locks in place so it cannot change adjustments. I also have a AAC 18T flash hider that will mount my 762SD sound suppressor. The flash hider will eventually be replaced with a brake, but as of this writing I did not find an 18T brake available. The Bolt Carrier Group will be a NiB BCG from Elite Tactical Advantage.
A couple of notes about the parts I have selected so far. I ordered everything but the trigger during the buying frenzy in Jan and Feb. The receivers were on order and I just received them so the parts have sat in a box waiting for the day to be installed. I had the gas block fitted to the barrel, and set the block all the way closed to check function. Blowing through the gas tube I found that it did not restrict flow. I called Syrac Ordnance to find out if this was normal, and was informed it was not. Syrac went above and beyond to help me out and sent out a replacement to use while mine is being repaired. That is good customer service, and I will continue to use their blocks in the future. Also, the BCG I received had excessive tool marks and seemed as though it was poorly manufactured.
I contacted Elite Tactical Advantage, and they also sent me a replacement part immediately. Both companies sent replacement parts without issue and were very apologetic. I feel that their great customer service is a testament to their companies. The firearms industry experienced an unprecedented volume of sales, so at the rate these companies were sending parts it is no wonder that a few parts were machined improperly or were assembled improperly. If you bought parts during this time, make sure you check them and ensure they function as they should. For the lower, I chose a standard AR-15 Carbine length mil-spec buffer tube.
I contacted Slashes Heavy Buffers and after a quick conversation about what the rifle was I was building, I picked up a spring and extra heavy buffer for the build. The lower required only a few small parts from a generic lower parts kit. (mag release, mag release spring, buffer tube detent and spring, safety detent and spring) I added a CMC 3.5 curved trigger that I am very fond of, and a Battle Arms Development ambidextrous safety. I have been a terribly cheap person for quite some time. I rarely spend a lot of money on things that others seem to enjoy. The Battle Arms Development safety was one of these items that I would not buy. I did not understand the need for such an expensive part. After using this safety for a few minutes it became quite clear that it is fantastic!
The safety not only looks great with the billet MKM set and functions very well. The B.A.D. Lever also makes the lower truly ambidextrous, minus the magazine release. The B.A.D. Lever is a nice touch to any AR-15/10 and makes manipulating the safety off and on easy. I see one of these for all of my AR builds in the future. The BCG and Gas block will be installed later this week, and the rifle will be test fired next week. Stay tuned for related articles about the optic I chose for this build, a US Optics SR8 with Horus reticule. Also look for an article about South West Ammunition .308 line up and how it performs in .308 ARs ranging from 16”, 18” and 20” barrels. This rifle will be my primary hunting rifle this season and will take lots of deer and hogs.
Thank you for reading and remember to give us a like on FaceBook. By Jason Hallmark
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Jason's love of shooting sports started at an early age hunting with his father in the pastures of West Texas. Jason is now Full Time Law Enforcement and shoots competitively when he can.