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.
Upper Receiver
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.
Charging Handle
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.
Barrel
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.
Gas Tube
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.
Gas Block
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.)
Excellent, and for me, timely. Thank you. Looking forward to the rest of it. Any pics to go with the article?
Sorry, but the author did not provide any photos.
Thank you sir.
Good topic and important info , thanks
I’m glad you are enjoying it so far. I spent a lot of time researching this topic and thought it would be valuable for many of us.
I’m happy to share my knowledge with you. I wouldn’t hesitate to build another LR-308. The assembly is even easier than the AR-15 as there are fewer roll pins involved. Due to the size of the lower many of the roll pins are replaced by threaded pins. This is a detail I found very convenient.
AR-10A/SR-25/M-110/LR-308
AR-10B [Converted M1A mag] GEN 1, new manufacture for GEN II
Armalite sells complete rifles using LR-308 mags [A series], comes with a PMAG, and still have parts for the B series. I suspect the Armalite A Series are compatible with DPMS standard, but I don’t know for sure???
Those of us that invested in the Armalite AR-10B series ended up on the wrong side of history. There is no conversion from AR-10B to AR-10A. Mags are not compatible and it is dangerous to mix the deployment of both types within a group.
The AWB was a terrible evil thing that hindered the development of firearms.
You are correct about magazine interchangeability. Just as with the Betamax versus VHS war, one maker had to lose. (And ironically, Betamax was the better format.) I recommend that any survivalist who owns an Armalite that is not compatible with the now quasi-standard LR-308 AR-10 magazines should sell or trade it off.
We have Armalite AR-10 rifles with sixteen-inch barrels.
Our glass is 4×14 and fixed 10.
We acquired these about two decades ago.
At the 600-yard range near the penitentiary at Ione, California, our rifles consistently produce two-inch groups at the limit of the property… regardless of the person pulling the trigger.
Using Black Hills Match and hand-loads, we are confident in this platform.
At a hundred yards, twenty-round boxes of 150-grain hunting go into a single hole.
Watch your back-stop; that ‘single hole’ punches all the way through the trunk of a two-foot tree.
Magazines?
We have a foot-locker of Armalite-converted steel M-14 magazines… I’m guessing maybe a couple hundred or so.
For our little tribe, owning and using firearms is a religious experience.
Show of hands… how many are attached to their firearms through a ‘spiritual’ bond?
And would never get rid of them for any reason?
Looking forward to part 2. I built one in 6.5 cm using a matched aero upper/lower.
Unfortunately, I bought a barrel from a company that got bought out since my build and received zero support on issues I had with chambering rounds.
It’s now at a smithy to figure out.
When it does chamber and shoot, I’m very happy with the groups.
If you have an Armalite AR10 B-series rifle and like it, don’t despair. There are proprietary Armalite magazines available, and while somewhat pricey, they are of excellent quality. Also, standard M-14 magazines can be adapted with a bit of light machining. Just make sure to mark your mags so as not to interchange them.
Very nice. :O)
While there is a mil-spec for AR-15s, there is by no means an industry standard on variations of that platform. I would say in today’s market there is almost as much exclusive variation in AR-15 at there is in AR-10/LR-308. But not really a significant issue, as anyone who looks to acquire such a fine machine in any of these platforms needs to exercise due diligence prior to purchase.
I have both AR-15 based platforms and LR-308. I have heavy barreled version for longer range work (up to 800 m in 556, up to 1,000 m in 308) equipped with sufficient optics. These are not my “Long range” shooters, but will get the job done at reasonable engagement ranges.
For patrol work, I have what I consider carbine length versions. They are equipped with ACOG sights typically used by DMs in a military unit. They are good to maybe 600 m, but more likely only will be used to 300 m or less. You have to have a pretty stable platform from which to shoot accurately enough beyond that range, and that’s not a practical consideration on patrol. I know of no one that shoots reliably off hand or kneeling much past 400 m, and those few I would call shooting zealots. I’m not that good and old enough to know I won’t get any better now.
Both my HB models are sub moa shooters if I can do my part. My little M4 variant is about 1 MOA on a good day, and my LR-308 carbine is somewhere between 1 and 2 MOA (closer to 2 I suspect). While both HB models weigh about the same in either caliber, the 308 carbine is noticeably heavier than the M4.
For a long time I was a proponent of the M14/M1A platform, probably from my time in the Navy during my early adulthood. I had acquired a Mini-14 in my 30s and thought that was fine for toting around coyote country. Basic, garand style action, paper thin barrel, but fairly rugged. Once the industry started spewing out AR-15s in real numbers and sufficient quality, I latched on to one of those and the techno-tweaker side of me came out and I got hooked. Then I got into competition shooting and that Mini-14 ended up in a friend’s gunsafe.
Nowadays I mostly shoot my Savage Mk II bolt gun or my H&K/Walther built 416, both in 22lr. Keeps me familiar with the platforms, and save me a lot of money and wear and tear on my primaries. Once in a while I will pull out the bigger guns, just to keep the dust off them and my brain. But ammo is getting hard to find, and I don’t have so much I can afford to shoot like I was when I was competing.
Mil-spec and industry standard are two important distinctions. I’ve built every AR-15 I own to Milspec but there are many rifles that have proprietary parts that don’t meet milspec. I have had great luck using AmmoSeek to find affordable ammo even with the high demand.
.308 is the old standard bearer, similar to Garang or 30.06. I also preferred the latter (06 was my most accurate cal). Creedmoor is like the new old faithful, just as the .308 is. Military always swear by it, the problem comes when one can ONLY shoot 1 cal… without the ability to know or adapt encase you need Grendel or Creedmoor.
I am seriously considering a 6.5 Grendel upper for one of my AR-15s. I’m a sucker for those short squatty cartridges.
If you want to watch a video that will make you smile all the way through, watch this:
https://www.youtube.com/watch?v=lvvbiPgGqpU
It is the original promotional movie from Fairchild Engine & Airplane Corporation for the AR 10. It is historic and incredibly informative. The YouTube video link is for a video produced by TAB – The Armourer’s Bench. The Fairchild promo begins at 9:32. If you watch from the beginning, realize the audio was overdubbed, so audio and video are out of sync. Did you know the AR 10 could also fire grenades?
Shoot when frozen, full of sand and water? WOW!
great article. my best battle rifle currently is my ar-10. aero precision upper and lower. i enjoyed figuring out the best buffer and spring to use. i will say that mine doesn’t like mil surplus 7.62 nato from the early 80’s as the primer is too hard. i followed the advice of JWR and stocked up on LR-308 AR-10 magazines. i prefer magpul and hex mags for mine. my rifle is ceracoted in the stylist Full Dark Earth (FDE) color and it took a while for it to like metal magazines.
I too prefer Magpul Pmags. They are affordable, reliable and more quiet than metal mags. I coated my rifle with a brownells product called aluma hyde-II. I’ve used this coating on multiple firearms and it has been easy to apply and durable. I also choose FDE. It provided great camouflage in s variety of terrains.
I will keep my mint 1943 Winchester M1 Garand, my 5.56 Colt Sporter Match HBAR, my 16″ M4 5.56 Palmetto PA-15. That way I don’t have to spend a fortune on .308 ammo, which costs WAY TOO MUCH MONEY to purchase! 75+77 grain match 5.56 ammo is my preferred food for these picky and hungry critters!!! Remember, I am just a common American, with limited finances. That means that I don’t ever waste ammo, and I make EVERY SHOT COUNT!
.308 is definitely more speedy than 5.56. In my mind it fills more of s specialized role as a dedicated marksman rifle than it would s patrol rifle. If I’m on shanks mare I’m going to grab a rifle chambered in 5.56. If I’m on an over watch or LP/OP duty I’m taking .308. I’ve found a few websites where I can get .308 for 70 cents a round shipped. I find this affordable enough to justify a .308 as s DMR and hunting rifle.
The AR-15 and LR-308 platforms are close enough that I can train with cheap 5.56 Ammo and crossover to the LR-308 without skipping a beat. I’ve built my rifles to roughly the same spec even though they are AR-15 and LR-308. Some of that 75 grain 5.56 is just as expensive as .308. Gold medal match is very comparable in price between .223 and .308 st least st my local gun store. However I can’t fault you for choosing a Garand.
All I know is that the sweetest rifle I ever handled was the M14. A long time ago. I still have dreams about that smooth weapon. Of course, my Uncle Sam was buying the ammunition for me.
Carry on in grace
The M14 is an awesome rifle. I considered buying [an M1A] but decided to part-up this LR-308 instead.
I’m glad to see my article posted on The birthday of Buck Owens. He is one of my all time favorites. Only You, Think of Me, My Heart Skips a Beat are some of my favorites. It’s refreshing to interact with the like minded people of this forum. Reading Survival Blog is something I look forward to each day.
Regarding the barrel, what is the rate of twist that you’re getting MOA out of it? I’ve been tempted to get the S&W M&P-10, however with a good supply of lighter weight 7.62mm ammo in 147 or 149 grain already on hand I was worried about accuracy with the 1/10 twist rate.
1:10 twist rate will stabilize 308 up to about 168 grain reliably. it will do marginally at 175 grain. All my 308 guns are 1:10.
My barrel is a 1:10 twist 18 inch barrel. Loves 150 grain Federal Power Shok. It also shot the Hornady American Gunner well just over 1 moa. I believe the American Gunner line is 155 grain. I shot some 180 grain federal fusion and it really opened up, 2 moa or greater. I haven’t chronographed any loads or worked up a load but I shot 7 or 8 different loads with various bullet weights. My gun seems to like lighter bullets, but I’m hoping to find a velocity node with a 165 or 168 grain bullet. I handload but I’m planning to shoot mostly factory ammo through this rifle.
bought a dpms 308 lr finaly got around to loading up some rounds shoots ok but will not eject the spent round now I know why it was a trade in at cabelas new into the ar platform bought it to compliant and use with my lane suppressor. any thing I should be looking to do