Some Important Facts Before You Build An AR-10/.308

Experienced rifle builders are well aware of the potential with the AR-15 with its huge range of interchangeable parts. Upper and lower receivers always seem to fit together well, parts kits match up with BCGs every time, and every .223 or 5.56 NATO barrel and chamber you source are guaranteed to fit almost any receiver. It’s customization heaven.

Building an AR-10 with a caliber like .308 is also very popular, especially with the introduction of the ready-to-fire uppers, the 80% lowers chambered in that calibre, and the range of available complete build kits. But the original AR-10 has few to no aftermarket components for sale, making a custom build a bit trickier. But what can you do to upgrade your rifle easily?

The AR-10 preceded the AR-15 and was scaled down to meet the needs of the military with the .223 round. Following the sale of the Armalite company to Colt, the military did indeed pick the weapon as their one of choice, designating it the M16, and creating as firearm legend.

This surge in interest in the smaller weapon led to the AR-10 kinda being placed on the backburner for some years, first at Armalite and then Knights Armament. At the same time, the Stoner-Rifle 25 (SR-25) was also taken up by the NATO military forces as a longer-range sniping weapon. Chambered for the 7.62×51 round this became quite popular and led to a resurgence in interest in the AR-10, though the SR-10 had much more in common with the AR-15. That said, many of the AR-10 and SR-25 parts are interchangeable, making them more popular weapons.

So, what do you need to know about AR-10’s if you want to build a custom job with an 80% lower receiver?

First off, the AR-10 is a family or platform that isn’t seen as a compatible product within itself, and that can cause problems. If you take any two AR-15 and compare them, the chance as pretty good that you will find them compatible. Not so with AR-10’s, unfortunately. Different companies create their own take on AR-10’s so don’t try and chop and change; it is likely not to work.

Next, you have to understand that AR-10 internal parts themselves are not always compatible. There are a number of different patterns for parts like barrels, which may be designed for Armalite and DPMS (otherwise known as SR-25 pattern), and upper receivers may be DPMS or Armalite, and don’t try fitting one onto the other, so don’t even try. Ideally, you should start off with your 80% lower receiver and build up from there so that you can be fairly assured of getting the right upper and then the correct barrel to go onto it.

Of course, if you are intent on going down the 80% lower routes also means you’ll need a specific jig. The jig must be matched to the 80% lower that you choose to fit the gun. It’s not like AR 15s where there aren’t the same kind of differences that can appear between builds. When you choose an AR10 80% lower receiver make sure you purchase the compatible 80% Lower Jig and the right set of tools to go with it too.

So, if you are planning on building you need to be aware that you need compatible parts but also really need to start with your 80% lower and build up from there. Because of subtle differences between different lowers there are several parts that are only compatible with AR10 lower receivers. Some small parts like the safety, trigger, and trigger springs can be swapped from AR10 to AR 15 without an issue but some parts are not so easy to swap. Parts that will NOT swap are the following.

• Bolt Catch:
  This device locks the bolt open after the last round is fired, allowing you to reload quickly.
• Takedown Pin:
  The Takedown Pin is the first pin you push in when you want to separate the lower receiver from the upper.
• Buffer:
  Quite simply, the buffer is the contact point for the bolt carrier to move rearward within the buffer tube. When the buffer spring recoils, it pushes the buffer and bolt carrier forward, thus loading the next round of ammunition and closing the bolt for the next shot.
• Magazine catch:
  It hold the magazine in place.
• Most Pistol Grips:
  You really need to know?

So, if you are starting an AR-10 build with the 80% lower receiver, you will need to check that these parts are going to be compatible with the rest of your gun, but if you do that, you’ll end up with a weapon worthy of the word.