AR-15 Parts and Pieces

The AR-15 is a popular sporting rifle that many firearm enthusiasts are finding are very easy to build and assemble. Today we’ll dive into the parts associated with an AR-15. While the goal of this article isn’t to teach you how to build an AR-15, it’ll certainly help you in identifying what you’ll need and other avenues of potentially building it.

This article is also important because it’ll help you troubleshoot issues after running your gun hard, potential errors by gunsmiths while assembling your rifle, and ways to upgrade certain parts to make it run better. With this knowledge in mind, your possibilities are endless for updates, upgrades, and fixes.

Routes to Building an AR-15

There are a couple different routes to building an AR-15.

Read: The Best Beginner AR-15 Rifle

The Cheater Method for Assembling an AR-15

The first is through a complete lower from a company like Spike’s Tactical or Aero Precision (there are many more). The lower receiver is the “controlled item” that you’ll need a background check or show your handgun license for.

These will often come with at least a buffer tube but could also include a buttstock as well.

You would then buy a complete upper. Make sure you’re following applicable state and federal laws so you’re not building an unlawful short barreled rifle (SBR) – as of 2021, you’ll need a tax stamp for that. After that – all you’ll need is:

  • Buffer spring
  • Buffer
  • Charging handle
  • Bolt carrier group
  • Magazine (because – how’re you going to feed ammo into it?)

Building an AR-15 from Scratch

This can be as customized as you’d like it. I personally prefer to build my lower receiver from scratch and then find the right complete upper receiver. But the list below will assume that you’re starting from scratch.

We recommend using’s assembly instructions and ar-15 parts diagram for your assembly needs. I’ve built a few rifles using their instructions and it’s fairly straight forward. Don’t be afraid to look up videos on YouTube either.

Purchasing AR-15 parts

Worth Firearms carries a local stock of all AR-15 parts. We have quick and easy shipping from distributors for anything you could possibly need – think of Worth Firearms when gathering parts for your next AR-15.

Lower Receiver Group Parts

Use’s lower receiver assembly videos and instructions to ensure your build goes correctly.

Stripped Lower Receiver

We’ll first outline the stripped lower receiver. This will be the most difficult to get – only because you cannot have it shipped direct to your home. You must pick this up yourself from a big box store (Cabela’s), gun store, or from a local FFL.

Aero Precision lower receiver

Many gun stores offer these stripped lower receivers but your selection might be limited. The stores carry a certain brand or a small variety of options. However, I feel that your best option is to buy direct from a manufacturer and have it shipped to your local FFL. Worth Firearms is certified to make transfers from manufacturers to your own possession through an FBI background check or use of your handgun license.

Lower Parts Kit

CMMG is the go-to manufacturer for lower parts kits. LUTH-AR is another popular lower parts kit manufacturer as well. These kits will typically contain:

  • Takedown Pin
  • Receiver Pivot Pin
  • Takedown Pin Detent (2)
  • Takedown Pin Detent Spring (2)
  • Hammer and Trigger Pin (2)
  • Hammer Spring
  • Trigger Spring
  • Disconnect
  • Disconnect Spring
  • Safety Selector
  • Selector Detent
  • Lock Washer
  • Pistol Grip Screw
  • Hammer
  • Trigger
  • Pistol Grip
  • Magazine Catch
  • Magazine Catch Spring
  • Magazine Release Button
  • Trigger Guard Assembly
  • Bolt Catch
  • Bolt Catch Plunger
  • Bolt Catch Spring Pin
  • Bolt Cat

Pistol Grip

Now – I’ll tell you up front that some lower parts kits can be purchased without the pistol grip. I’ve seen a couple varieties of pistol grips, one with a tang and one without. I think the pistol grip without the tang looks better but it’s really a personal preference thing.


You should also consider the trigger – the lower parts kit will have a trigger and all the parts to assemble it. However, I prefer to use a CMC drop in trigger.

CMC Trigger

It’s not worth the hassle of getting the trigger complete right – something I’ve only been able to do once. I suggest buying a new trigger or having a gunsmith do your trigger. Who knows, maybe you’ll have better luck than I did.

Other popular trigger brands include Geissele, Timney, and TRIGRTECH. Be sure to consider whether you’ll want a single or double stage trigger. Also important when choosing a trigger is the trigger weight.

Buffer System and Stock

These aren’t included in the lower parts kit. You’ll need to purchase a:

  • buffer tube
  • buffer spring
  • buffer
  • Stock

All of these parts depend on the length of your barrel. Current ATF guidelines say that your rifle must have a barrel of at least 16″ and an overall length of at least 26″.

If your barrel is less than 16″ or your overall length is less than 26″ you’ll need to use a pistol brace. In 2021, there are talks that the ATF will institute a ban on pistol braces. Be sure to comply with federal, state, and local laws.

AR Pistol brace

Ensure your barrel length is compatible with the weight of your buffer and is supported by the strength of your buffer spring.

Upper Receiver Parts

The upper receiver group for your firearm is the part that includes the upper receiver, the barrel, fore-end, the bolt carrier group and the carrying handle/rail.

Stripped Upper Receiver

Unlike the lower receiver, the stripped upper receiver does not require an FFL for transfer. Be sure to find the right upper for the caliber you plan to fire.

Upper Receiver Parts Kit

This kit comes with pieces to add your forward assist and ejection port cover. It’s pretty standard stuff. Relatively easy to assemble on your upper receiver.

Barrel, Gas Tube, and Gas Block

The barrel of any AR-15 is an important part to pay attention to. You can go nuts buying carbon, fluted, specialty barrels or you might stick with your typical stainless steel one.

After purchasing your barrel, be sure to purchase the right length gas tube and gas block. You need to do your research here and make sure the gas tube and gas block are the right components for each other. Also – ensure the gas block and gas tube will work with your handguard size/length. When researching barrels on Rosco Manufacturing’s site, I noticed they told me the gas system specs I needed. I suggest you follow the manufacturer’s recommendations on gas tube and gas block specs.

An adjustable gas block can allow you to control the recoil and accuracy.

Buy the right gas block for your gun's gas system

Muzzle Device

The Muzzle Brakes could reduce recoil by up to 50%. A muzzle device will vent gas horizontally allowing for clear vision. Flash shields protect from muzzle flash and are the bare minimum you’ll need for a muzzle device.

You’ll want to find the appropriate device if you’re planning to mount a suppressor onto the weapon as well.

Handguard Options

AR-15’s typically have two options for handguards. One is a mounted system that touches is fixed to the barrel or one that is free floating. If you run your rifle hard enough, the affixed handguard is said to hurt your accuracy.

While I understand this is more of people who run their rifles hard, I’d say the Marine Corps has gotten along just fine with affixed handguards. Many people in my boot camp platoon shot near perfect rifle range scores with these handguards.

Another option is the free float handguard. This attaches via bolt to the upper receiver and doesn’t touch the barrel at either end of the weapon. It’s no secret that we like Aero Precision builder sets, and these sets often come with a free float handguard.

Free floating handguard

Bolt Carrier Group and Charging Handle

There are many parts to a bolt carrier group. It’s safest to say you likely won’t be building this yourself. You’ll buy the group pre-assembled and plug and play. You can find a good explanation of the pieces online. You may need to replace the firing pin but it truthfully won’t happen unless you’re running you gun harder than most people or beyond 20,000 rounds downrange. Again – I like Aero Precision here but there are many other brands to look at like CMMG, Colt, Odin, Surefire, etc. There are different bolt carrier group sizes, make sure you’re purchasing the correct one.

It seems like the charging handle is a matter of personal style. I’m a fan of the ambidextrous ones like Radian’s Raptor charging handle. You can find different styles of charging handle by the same manufacturer. We suggest the following brands of charging handle: CMMG, Seekins, LUTH-AR, BCM, and Radian. Again – the charging handle will get the work done – your charging handle is personal to you. Choose the right charging handle for your style.

Iron sights and optics

The last basic components needed is some type of sight, optic, or scope. As a Marine – we used an iron sight for up to 500 yards. I these are primarily for bragging rights at this point. There are so many affordable optics and scopes available to civilians that you might as well buy one.

We sell scopes and optics from Sig Sauer and other manufacturers. There’s a wide range of options from low end to high, short distance to long distance.

Using a scope or optic is fun but still focus on the fundamentals or else the finest piece of optics won’t help you place lead on steel.

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