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How to Build an AR


There is no doubt that the AR platforms are one of the most popular rifles on the market today. They come in a wide variety of calibers and set ups, which can usually be found at local gun shops or bigger hunting goods box stores. However, sometimes, as gun enthusiasts, we just want more than what the gun store can offer.

While buying a completely manufactured AR-platform rifle might be the quickest and most logical option to adding another firearm to your collection, the thrill and enjoyment of planning, designing, and assembling your own AR style rifle might be more of what you are looking for. If that is the case, but you do not exactly know where to start, you are in the right place.

Building an AR-platform rifle of your own might be a little intimidating at first glance but can easily be done and could ultimately save you money in the long run. Plus you get the benefit of saying you built your own firearm exactly the way that you wanted it.

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Before You Get Started

This will be a very basic guide to what you need and how to assemble an AR. Be sure to do your own, in-depth research to know exactly what you are getting into before you start. The last thing you want to do is purchase all the pieces and parts and then realize you do not have the skills, patience, or tools necessary to complete the build. So here are a couple of things to keep in mind.

Tools Needed

You will most definitely need some tools and some specialty tools at that. These include:

  • Bench vise
  • Receiver block for mounting the lower receiver while you build
  • Roll pin punches
  • Roll pin holders
  • Small brass hammer
  • Needle-nose plier
  • Roll pin pusher
  • Castle nut wrench
  • Painter’s tape
  • Gun oil

More tools may be necessary if you decide to do some more in-depth building, like using a stripped lower raeceiver, but we will touch on that a little later. Tools can be an added expense if you do not already have these, but if you plan on building multiple guns in the future, they are well worth it.

What Caliber?

Deciding which caliber to build your AR around is vitally important. Do your research for the type of shooting you are looking to do and then do your homework on which platform you will need. AR-15 platforms handle a large variety of different calibers while other, larger calibers might need to go to the AR-10 platform which is larger and heavier.


Make sure that as you plan out your build, the parts you are ordering will work with one another. The different manufacturers for AR style parts do not always work well together. It might be best to stick to using one or two companies that you know their products are compatible with one another. You do not want to be halfway through a build and find out that a couple of your parts do not line up and work together.

Getting Parts

The nice thing about an AR build is that almost all of the parts can be bought and ordered online and then shipped directly to your front door. The only part that you cannot do this with is the lower receiver. Gun laws state that the lower receiver is that actual mechanical part of the firearm and thus cannot be shipped directly to the consumer.

Instead, the lower receiver needs to be shipped to a licensed dealer with an FFL. That means you can order it online, but you have to provide information to the seller on where to ship the lower receiver. Your local gun shop should be able to handle that for you for a small fee. This is the same process you would go through if you purchased a gun online and had it shipped to your local FFL for pickup.

This is going to be one of the most vital pieces of the AR build, so make sure you have this information ahead of time to make things go smoothly.

Cost and Perks

Cost will vary widely depending on what you decide to put into your build. The nice thing about building your own AR is that you dictate what goes in and what does not and how much your budget will allow you to do. A basic AR build can easily be done for under $1,000, but if you want all the bells and whistles available, expect to spend more.

You are saving yourself a bit of money by doing the work yourself. If you bought the rifle you are going to build already put together, it would cost significantly more. This might allow you to get more of those perks and benefits that would be very costly when buying it from the gun shop.

You also get the knowledge of exactly how your AR will work and operate along with how to maintain it. Also, if you are on a budget, you can know and plan exactly how to upgrade your AR later and already have the tools and know-how to do the work yourself.

Parts You Need To Build Your AR

There is a list of parts that you will want to gather before you physically start building your AR rifle. Not every AR that you decide to build will need this exact list, but this list is for the popular M-4 style AR-15 that has the most custom work. Once we go through the list, we will then touch on each part of the build briefly to give you an idea of what kind of work needs to be done.

Parts List

  • AR-15 Lower Receiver
  • Lower Receiver Parts Kit
  • AR-15 Upper Receiver
  • Upper Receiver Parts Kit
  • Bolt Carrier Group
  • Barrel and Gas Block/Gas System
  • Handguards
  • Buffer Tube, Buffer, & Spring
  • Grip & Buttstock
  • Charging Handle
  • Other Add-ons

Carefully plan out what parts you will need and what things you want to add on to your AR rifle. Do your research on the parts and do not guess. There are tons of information out there that will expand on the basics of building an AR that we will cover.

Your AR Build Step by Step

For the purpose of staying as basic as possible about the steps, we will talk about each part of the build briefly.

Lower Receiver & Parts Kit

When choosing a lower receiver, you have two options: a complete lower or a stripped lower. The complete comes with everything you need already assembled while the stripped lower needs more work and more specialized tools but allows for more personalization.

A complete lower receiver is pre-assembled with a trigger assembly, safety, and mag holder already in place. Sometimes they also come with a buttstock and buffer tube as well, but for this case, we will say it does not. The complete lower is a better option for those new to gun building.

The stripped lower is basically just the mag well and the metal that encases the parts mentioned above. Everything else in the complete lower needs to be added and takes some fine machining work. This allows for more personalization, but also requires meticulous work and attention to detail. You will also need a lower receiver parts kit to complete the receiver. This also includes the trigger, which is a huge adjustable and personalized piece of an AR build for a lot of people.

Upper Receiver & Parts Kit

Like the lower receiver, the upper receiver has multiple options as well: a complete upper or a stripped upper. The complete upper comes ready to go with everything you need while the stripped upper is customizable but takes much more work and tools plus a parts kit.

The complete upper has the barrel, gas system, and handguards already attached. It is ready to just put together with the lower receiver, which makes it great for beginner builders.

The stripped upper needs all the above-mentioned parts which take more know-how, tools, and time but again allows for more personalization and improved parts. You can still customize a complete upper, but not as much as a stripped upper.

Bolt Carrier Group

The bolt carrier group is a huge part of the AR rifle as it is responsible for firing, ejecting, and loading rounds. There are tons of options out there on the market, but look for one that is really reliable and will hold up to a lot of use.

During this part of the build, you will also want to install the charging handle, which helps manually run the bolt carrier group. This is also a great time to put a dust cover on, if you wish. This is optional, but not mandatory.

Barrel, Gas System, & Handguards

If you choose to go with a stripped upper receiver, you will need to build one out completely on your own. This includes the barrel, gas system, and hand guards.

For the barrel, you will need to choose the caliber, length, materials, rifling, and twist rate. This is where personalization can really be fun to play with to get exactly what you want out of an AR.

The gas system is super important to the operation of the gun as it is what uses hot gas from firing the gun to force the bolt carrier group back, eject the spent cartridge, and chamber a new round. There are a variety of types of gas systems to choose from and you will need a specific length to match the length of your barrel.

Handguards are more of a cosmetic piece, but are essential to operating the AR safely. This is where you can customize as much or little as you want.

Rifle with sling

Buffer Tube, Grip, & Buttstock

This is all the parts needed for the rear stock of the AR build from the lower receiver to your shoulder. This is the main part for helping you stabilize your AR and feeling comfortable behind it. The grip and the buttstock are completely customizable to what you are comfortable with and are easy to attach.

The buffer tube is the most important part of this section, as the buffer and spring must be balanced based on the force transferred from the gas system. Make sure you do your homework for your barrel length and gas system used. Also, various buffer weights and spring strengths will effect the rifle performance.

Other Add-Ons

Once the main parts of the firearm are assembled and put together, it should now be a functional AR. The final step is to add the personalized pieces that make it YOUR weapon.

This will include things like picatinny rails, sights, muzzle breaks, and a sling. Personalize these as you would like in any combination. The sky is the limit!

Picatinny rails will allow you to add more equipment and attachments to your AR like sights, handles, and flashlights or lasers. Sights can be equipped as scopes, red dots, iron sights, or a combination of any, depending on your intended use. Muzzle breaks add to the great look of the AR as well as being functional in cutting down recoil for quicker, more accurate follow-up shots.

A sling might not seem like a huge thing, but it can definitely make or break the comfort of your AR build. Flatline Fiber Co. makes great slings for AR platforms that are comfortable, durable, and highly functional without breaking the bank. Their quick detach swivels are also a great addition for quickly transitioning between the sling and not using the sling. If you plan on using your AR a lot, a sling is a must have.

Wrapping Up

Now, this was a very basic overview to building your own AR, but it should give you an idea of what you are looking to get into. Depending on how in-depth you want to get into your build will determine exactly what you need to do.

If you are new, buy pre-assembled pieces to learn the ropes. Then perhaps get into doing a full, ground-up, build. Either way, you will save money and get more personalization out of a build compared to a manufactured AR, and you will learn a whole lot along the way.

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