How To Build An AR15

Welcome To Our AR15 Build Guide

Building an AR15 is a lot of fun. There are tons of options available, and in the process of building an AR15, you will also learn a ton about this firearm platform.

Before building an AR15, you probably have an idea on what type of rifle you want to build. 

  • Home Defense
  • High Volume Range Training Rifle
  • Hunting
  • Clone Projects
  • Precision Shooting
  • Competition Shooting

The biggest difference among all these build options is the weight, tactical capabilities and cost. What you choose to put on the rifle matters. There is no exact science to it, but there are some guidelines to follow to build a reliable rifle to fire.

What This Is Not

This guide focus on building a practical rifle with core components. This is not about building super Gucci rifles with expensive parts as collector items. Additionally, this guide does not provide instructions for constructing an ultra-precise rifle using advanced gauge tools, as that topic exceeds the scope of this guide.

Everything discussed here is to build a practical rifle for home defense and range training.

Assuming you already have all the tools required to build an rifle. Here are 3 important stages of building an AR15 rifle:

  • Build Upper
  • Build Lower
  • Customize Accessories

Building The Upper Receiver

The upper receiver include:

  • Barrel
  • Muzzle device
  • Gas block
  • Gas tube
  • Stripped upper receiver
  • Bolt carrier group
  • Charging handle
  • Handguard
  • Iron sights

It is important to select high-quality parts and understand when to save money and when not to compromise quality for cost.

While most AR15 parts fit with one another, however we highly recommend pairing the same brand bolt carrier group and barrel together. An out-of-spec barrel chamber or bolt carrier can result in avoidable friction, improper lock-up, and potential damage, ultimately leading to compromised accuracy.

Because they come from the same spec requirement, they generally have the best tolerance.

Install The Gas Block First

Installing the gas block is must before installing muzzle device. Many people get this part wrong, and they had to redo the whole thing.

Ensure you dimple the barrel using a high precision gas block jig. The dimpled spot will enable the gas block set screw to lock up tightly to the barrel. This step is crucial because we don't want the gas block to tilt or become misaligned with the gas port on the barrel when firing. Remember, this is a high-stress component that requires everything to be tightly secured. 

Some builders even pin the gas block to the barrel for reassurance. 

Install The Gas Tube 

Slide in the gas tube to the gas block and insert the roll pin to secure the installation. Be sure to orientate the gas tube correctly so the opposite end goes into the upper receiver hole.

Be sure to purchase the appropriate gas tube length based on the gas length of the barrel.

Install The Barrel

Slide the barrel to the upper receiver, then tighten the barrel nut provided by the handguard to secure the barrel to the receiver. This step must be done on a super sturdy work bench while using a reaction rod when applying torque. (40 - 50 ft lb of torque). If you are using a barrel nut without the timing gear, then you don't have to worry about aligning for the gas tube to go through.

We highly recommend the Midwest Industries AR15 reaction rod because it provides the tightest fit to prevent receiver warping. It also keeps the barrel aligned during torquing and prevents shear stress on the barrel index post. (This tool also helps you to identify if your upper receiver is mil-spec or not, if loose, then it's not up to mil-spec tolerance)

One major detail here is to use a go or no go gauge to ensure your specific barrel meets the chamber headspace requirement to make your gun's safe to fire. 

Install The Muzzle Device

Installing the muzzle device is a straightforward process. First, securely clamp the barrel on a rock solid vice block using the reaction rod. Next, apply torque (30 ft pound) to fasten the muzzle device in place.

However, certain compensators can be more challenging to install. You may need to add shims and ensure proper timing to get ports in alignment. Achieving the correct alignment might take some time, so be patient and take your time to get it right. 

Installing Bolt Carrier Group

Almost all bolt carrier group is preassembled. All you have to do is slide it into the upper receiver with the charging handle and you are good to go.

Install The Handguard

Installing the handguard is very easy as long as the barrel nut is secured. Most barrel nut have slot positions to either screw in the handguard mount or clamp it down tight.

Building The Lower Receiver

Building the lower receiver is actually very easy, and the only part that needs torque is the castle nut on the buffer tube.

The lower receiver has the following parts:

  • Takedown pins
  • Takedown pins detent 
  • Fire selector 
  • Fire selector spring detent
  • Pistol grip
  • End plate
  • Magazine release button
  • Magazine release spring
  • Bolt catch
  • Bolt catch pin
  • Buffer tube
  • Buffer spring
  • Recoil buffer
  • Buffer retainer pin
  • Trigger group (Hammer, sear, trigger bar)
  • Trigger guard

Installing Takedown Pins

Takedown pins holds the upper receiver and the lower receiver together. The front pin is generally easier to install, and the rear pin requires the buffer end plate to secure it in place.

Both takedown pins need spring detent to hold it in place. Once the takedown pin is snapped in place, it will not come out. The same goes for the rear takedown pin, unless the end plate is removed. 

For this, we highly recommend using the Real Avid Master Bench Block to hold the receiver in place when trying to hammer any roll pins in.

Installing Trigger Guard

If you lower receiver features integrated trigger guard, then you can disregard this step. If not, installing a trigger guard that can fit the trigger finger even when wearing a pair of gloves. The trigger guard is held by one small roll pin and one small set screw. It's very easy to install.

Installing Bolt Catch

The bolt catch is spring loaded and its main job is to lock the bolt to the rear simultaneously interact with the magazine follower when the magazine runs empty.

The standard bolt catch release paddle is attached to the lower receiver using a single small roll pin. The roll pin is located in a tight corner of the receiver, making it important to take precautions while hammering it in. To avoid scratching the receiver during this process, you can place painter's tape around the area before hammering the roll pin.

Installing Magazine Release

The magazine release is very easy to install. Simply screw on the magazine release button and then push the button down while screw in the magazine catch from the other side until it fits right into the slot.

Installing Buffer Assembly

There are many buffer assembly available on the market, and the most common ones are mil spec and commercial buffer tubes. These buffer tubes all thread into the lower receiver.

First, install the buffer retainer pin in the lower receiver. The goal is to thread the buffer tube until the buffer tube can retain the pin. This pin is designed to hold the buffer in place.

The castle nut will go on the buffer tube first, then the buffer tube goes onto the lower receiver with the end plate in between. Torque the castle nut with the REAL AVID Master Wrench up to 40 ft pound, and you are done.

Align the buffer tube, then tight down the castle nut while keeping the buffer tube aligned. The end plate will push the spring loaded detent to hold the rear takedown pin.

Finally, put the recoil buffer spring and buffer inside the buffer tube, and you're done.

Stake The Castle Nut

Staking the castle nut prevents the nut from turning or getting loose. Make sure your castle nut has deep 45 degree notches for the material to displace. We highly recommend staking in at least 2 spots.

Install Butt Stock

If you have a mil-spec buffer tube, then you can only attach a mil-spec stock.

If you have a commercial buffer tube, then you can fit on both commercial and mil-spec buffer tubes. This versatility allows users with either type of buffer tube to select from a wider range of stock options.

Installing Trigger

If you have a drop in trigger group, then this part is very easy. 

Simply, just drop in the trigger group and install two small trigger pins to hold the trigger in place. We highly recommend to use anti walk pins to secure the trigger in place to prevent unnecessary stress from the steel roll pin grinding on the aluminum receiver hole.

Next, install the fire selector whether be 90 or 45 degree.

Installing Pistol Grip

Before attaching the pistol grip, be sure to install the fire selector detent along with the spring in place. Their job is to hold the fire selector mode in place.

Then install the pistol grip. The pistol grip will exert tension on the safety selector detent spring to hold it in place. 

At this point you should have a finished lower receiver to mate with the upper receiver.

Attaching Accessories

Mount Optic

When it comes to optic, there are tons of options based on what your rifle is designed to perform. CQB? Long range? Mid range? Please visit this guide for more detailed recommendation.

Mount Light Accessories

Adding a light to the handguard is a must for any tactical and home defense AR15s. A light can help the user identify targets in low light and deter threats. It can be used as none lethal weapon in some personal defense scenarios.

Click here to learn more

Mount Handguard Accessories

For a lightweight AR15 build, keep the handguard as light as possible even if it's slotted for the entire length. Add a sling attachment point, a durable light and a ergonomic foregrip are plenty to get started.

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