The arguments for .308 Winchester over 5.56 NATO are well known and far spread through many internet forums. Undoubtedly many of you realize the advantages in firepower of the .308. We know of the incredible amount of reloading data, DOPE, and other consumer information available from the .308 community. This information will help you find a load that meets your needs or give you a great starting point to load your own high quality ammunition. If you have decided to invest in a weapon chambered in .308 Winchester chances are you have seen rifles being referred to as AR-10 or LR-308. I hope that this article can help you better understand what those designations mean and more importantly the components of these weapons systems.
AR-10 Versus LR-308
The purpose of this article is to lay out the advantages and disadvantages of the AR-10/LR-308 weapons platform. I will begin by giving a brief background that many of you are undoubtedly familiar with. The AR-10 is the predecessor of the AR-15. Eugene Stoner’s original design was built around the .308 cartridge, but the military asked for a scaled-down model based on the .222 Remington cartridge which at the time was one of the go-to cartridges for accuracy. This request led to the 5.56 NATO cartridge and the AR-15 we know and love today. Technically anytime the terminology AR-10 is used it should refer to Eugene Stoner’s original design which is now produced by Armalite. There are many other manufacturers who produce their own version of the AR-10 these rifles should be referred to as LR-308.
No Milspec for LR-308
The AR-15 has been mass-produced to exact specifications because of its use in the military. Unfortunately, things are not so cut and dry for it’s older brother, the AR-10. Gun owners and manufactures alike have realized the advantages of the weapons platform. This has led to many different versions based on the AR-10 not all of which are compatible. There are various companies such as SIG-Sauer, Palmetto State Armory, Aero Precision, DPMS and many others that produce their own LR-308 rifles. What adds to the confusion further is the fact that these rifles do not share compatibility with each other. Unlike the AR-15 platform where you can take parts from various rifles and combine them without issue, at least in theory. This is due to the fact that there is no mil spec as previously mentioned.
DPMS or Armalite
Although there is not a standard set of specifications there are two frontrunners as far as design and specifications are considered. These are the AR-10 produced by Armalite and the LR-308 produced by DPMS. The two platforms are often referred to simply as AR-10 style or DPMS Style, many but not all AR-10/LR-308 rifles follow one of these patterns. However, there are many others that are completely proprietary. This complicates assembling your own rifle beyond the lego-like assembly of an AR-15. One must do their research and really know what parts they are trying to put together and what platform they are designed for.
A guide to AR-15, LR-308 Compatibility
This incompatibility of parts intimidated me from assembling my own rifle for years but after much research I finally decided to give it a shot. I think my experience could help alleviate the uneasiness that some of you might feel when considering parting up your own rifles. I would also like to provide a few things to consider when purchasing the components for a rifle. There are many schools of thoughts and purposes for a rifle. I’m not pretending I have all the right answers or that I have built the perfect rifle. I don’t believe there is one rifle that can do it all. The rifle I built fits my needs and your needs might differ greatly.
Why I chose DPMS Pattern
I chose to build a rifle based on the DPMS platform because of the availability and cost of parts, the aftermarket support for the AR-10 platform is rather scarce. At the time of the build I had seen many parts built for a DPMS style LR-308 by reputable companies that I have had good experiences with in the past. The “LR” denotes a large frame AR-15. I’m one to stick with companies that I know are good rather than try and find the next great thing, if it’s not broke don’t fix it. My goal with this rifle was to build a lightweight rifle that I could use for hunting, mid-range shooting, and home defense. I pray I never have to use it to defend my home but I would rather have a gun and not need it then need a gun and not have it. With the current state of our country it’s not much of a stretch to imagine a time you might have to defend yourself from rioters, looters, or some kind of criminal.
I placed a big emphasis on weight because many complete rifles you can buy at your local gun store are very heavy, 10-12 pounds is very common for an LR-308. Through careful consideration I was able to keep my rifle under eight pounds (excluding magazine and optic). I will now dive into the individual components of a DPMS style LR-308. I want to make it clear that I paid for all of these parts with my own money and I’m not sponsored or supported by any of the following manufacturers or distributors. I’ve broken this up by the components of the upper and lower receiver to hopefully make things easier to follow.
Upper Receiver Components
The Upper Receiver is made up of the Bolt Carrier Group (BCG), Charging Handle, Barrel, Barrel Nut, Hand Guard, Forward Assist, Dust Cover Assembly, gas tube, gas block, muzzle device and the Upper Receiver itself. All of these parts are going to be different than your standard AR-15. This is simply due to the size of the .308 Winchester cartridge. The barrel and bolt face are obviously larger in order to accommodate the larger size of the .308 Winchester.
I chose to source an Aero Precision upper receiver because they are DPMS Style which means there are more compatible parts to this receiver that aren’t all made by Aero Precision. This allowed me to source parts online from places such as Midway USA, Brownells and Optics Planet at a much lower price than buying directly from a big name manufacturer. It also allowed me to decide which components I wanted to upgrade.
Forward Assist, Charging Handle and Dust Cover
The forward assist, charging handle and dust cover assemblies are fairly lightweight and sufficient for my needs without upgrade. Thus, I elected to save some money and bought these at a low price from Midway USA.
Bolt Carrier Group
There was a lightweight bolt carrier group manufactured as part of the Eugene Stoner line (named after the designer of the AR-10 and AR-15 weapons systems) so I also picked this up on Midway USA. The bolt carrier group is a great place to save weight on your build. There are many great options for a lightweight BCG.
With weight and budget in mind, I elected to purchase a standard Charging Handle. There are lots of awesome ambidextrous charging handles but they get spendy and I can always elect to purchase one later on. For now, the standard charging handle meets my needs.
Your choice of barrel is another great place to save weight as they can be extremely heavy. I opted for an 18 inch Faxon Firearms lightweight barrel. These barrels have a tapered contour giving them more metal towards the barrel extension. It then thins out until it hits the gas block. At the gas block it becomes “beefier” again. It’s important to have some heft at the barrel extension and gas block because these areas see the most heat. The extra heft at these locations acts as a heat sink which helps keep the barrel cool. This barrel has been excellent, it’s lightweight which helps the rifle balance extremely well and it can shoot. I have seen 1 MOA accuracy at 100 yards with 150-grain soft point ammunition that is cheap and abundant. I subscribe to the “buy it cheap and stack it deep” mindset.
The gas tube I chose was again a run of the mill standard gas tube. There’s a great debate out there about if you should run a nitrided gas tube or not. Nitride is a metal finish that will allow the gas tube to operate at higher temperatures. At first glance this seems to be a good option. However, the weapons system was designed with the gas tube as the weak link on purpose. The thought process here is if your gas tube doesn’t fail at high temperatures your barrel will likely overheat, droop, and cause a catastrophic failure, leaving you upriver without a paddle or in this situation SHTF without a rifle. The flip side to this is if the gas tube fails you, then you can still operate your rifle as a single shot, meaning you can fire a round, run the charging handle, manually extract a spent case and load a fresh one. For this reason I don’t run nitrided gas tubes. It is important to point out that the only time you are going to see gas tube failure is likely under sustained fully automatic fire. One YouTuber has shot 700 plus rounds of fully automatic fire through a rifle before the gas tube failed. Chances are your gas tube will never fail you. It does give me peace of mind knowing that if my gas tube ever gave up the ghost I wouldn’t be completely out of the fight.
In the past I have had issues with inadequate gas blocks — mostly of the adjustable variety. This experience led me to upgrade my gas block to something a little more robust. I chose to buy the Geissele Super Gas Block. This gas block has the regular set screws but it also has a roll pin that requires installation by a gunsmith, this installation is referred to as bombproof by Geissele Automatics. All this extra trouble is to ensure that your gas block doesn’t become loose, twist, and move away from the gas port in the barrel.
(To be concluded tomorrow, in Part 2.)