How To Build an AR-15 Rifle

Deciding which AR-15 to Build

Before you buy your first part, decide what kind of rifle you want. Will you be varmint hunting, plinking or competition shooting? Once you make this decision, you know what type of upper receiver and barrel you will use. The upper receiver and barrel you choose will determine the remaining parts needed.

Here are several types of stripped upper receivers, each with different features for different applications.

AR-15 A1 - Has a fixed carry handle, shell deflector and requires the installation of the forward assist assembly, ejection port cover assembly and the A1 sight assembly that allows only for windage adjustment. This upper is ideal to build a "Retro" civilian version of the Vietnam era M-16 Rifle.. AR-15 A2 - Has a fixed carry handle, shell deflector and requires the installation of the forward assist assembly, ejection port cover assembly and the A2 sight assembly that allows for windage and elevation adjustments. This is a popular upper to use for building a rifle for use in shooting matches. AR-15 A3 - Has a flattop with picatinny rail, shell deflector and requires the installation of the forward assist assembly and ejection port cover assembly. This is the current military upper and is used to build a civilian copy of the M4 (carbine with 16" barrel) or M-16 A4 (rifle with 20" barrel). Also great for building any type of Varmint or Target Carbine/Rifle since any type of optic can be mounted to the Flattop. AR-15 Flattop - Has many configurations for the upper receiver with various heights of picatinny rails for mounting scopes. These generally do not accommodate the forward assists or Ejection Port Cover assemblies or also known as the "Slick-Sided" uppers. The Flattop is great for building any type of Varmint or Target Carbine/Rifle since any type of optic can be mounted to the Flattop.

For your project, we decided to build a Varmint Rifle in 204 Ruger. Since we want to scope your rifle, we do not want an upper receiver with a carry handle, nor do we need open sights. That rules out the AR-15 A1 and A2. Therefore, either the AR-15 A3 or the Flattop will do. We chose the A3 because of its versatility. In addition, since we are building a Varmint Rifle designed for accuracy, we want to install a bull barrel with a free-float hand guard.

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Purchasing AR-15 Parts

Now that we have selected the type of upper receiver (A3), we know we need the forward assist assembly and Ejection Port Cover assembly. These parts would not be required had we selected a Flattop. In addition, since we are using a bull barrel with a free-float hand guard and without sights, we need a gas block but do not need a flash hider. Had we decided to use open sights, your front sight would have had the gas block built in. The free-float hand guard does not require the use of a delta pack or hand guard cap, as these are integral to the Free Float Tube hand guard.


Use our AR-15 Schematic for parts identification

AR-15 Upper Assembly Model 1 Upper Receiver Stripped DPMS Forward Assist Assembly DPMS Ejection Port Cover Assembly DPMS Bolt Carrier and Key DPMS Bolt Cam Pin Ar-Stoner Firing Pin, Retaining Pin DPMS Charging Handle DPMS Charging Handle Latch Spring DPMS Charging Handle Latch Shilen Drop-In Match Barrel with Bolt DPMS Gas Block DPMS Gas Tube DPMS Gas Tube Roll Pin JP Enterprises VTAC Modular Free Float Tube Handguard DPMS Ejection Port Cover Pins

Click on a product in the image to see more information on that part.

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Before You Build Your AR-15

Please remember these important things:

  • Safety - Always remember to wear safety glasses. Pins and springs can (and probably will) fly across the room. A shop apron is also helpful to protect your clothing.
  • Work Surface -Be sure to work in a well-lit area with plenty of clear, clean workbench area. Place a mat like the Tipton Gun Cleaning and Maintenance Mat over your work area to keep parts from rolling around or getting lost. The mat will also help protect your guns and parts from potential damage.
  • Floor Area - Since we are working with several springs and small pins, it is likely some of these small parts will find their way to the floor. If you have a clean floor or even if you place a white towel or some plain covering on the floor, it will be easier to find these small parts. Nothing is more frustrating than having to delay your project because a $ 0.99 roll pin vanishes.
  • Tools -There are several tools necessary to do a professional job. Please don't skimp here, as the quality of your work will suffer. Use the right tool for the job. Try to use brass punches whenever possible to reduce the chance of marring the finish.
AR-15 Upper Assembly Tools Screwdriver Sets Bench Vise and Clamps Punches Brass Punches Loctite Shooting Glasses Cleaning Utility Brushes Gunsmithing Fixtures Hammers Roll Pin Starter Punch Action Block Torque Wrench Adhesives and Solder Takedown Wrench Gun Cleaning and Maintenance Mats

Click on a product in the image to see a product listing for that part.

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Start Building Your AR-15

Make sure you have a good AR-15 schematic to use as a guide in assembling your upper assembly. The schematic is helpful in finding the correct names of parts and determining what they look like.


Spread out your Tipton Cleaning and Maintenance Mat
  • Arrange all your tools on your workbench so they are easy to access.
  • Arrange all your parts on your mat.
  • Group your parts together by assembly or with related parts. Refer to the pictures to aid you in this grouping process.
AR-15 Upper Assembly (without Barrel Assembly) Model 1 Upper Receiver Badger Ordnance Tactical Charging Handle Latch DPMS Charging Handle DPMS Charging Handle Latch Spring DPMS Forward Assist Assembly AR-Stoner Firing Pin, Retaining Pin DPMS Bolt Cam Pin DPMS Ejection Port Cover Pins DPMS Ejection Port Cover Assembly DPMS Bolt Carrier and Key

Ar-15 Upper Assembly (without Barrel Assembly)

Install Forward Assist Assembly on Upper Receiver
1. AR-15 Forward Assist, Forward Assist Spring and Forward Assist (Roll) Pin This assembly consists of:
  • Forward Assist
  • Forward Assist Spring
  • Forward Assist (Roll) Pin.
2. AR-15 Upper Receiver Turn Upper Receiver upside down so the picatinny rail is against the work surface.
3. AR-15 Forward Assist Pin and Forward Assist Slide the Forward Assist Spring on the Forward Assist (direction does not matter).
4. AR-15 Forward Assist Pin and AR-15 Upper Receiver Start the Forward Assist Pin into the bottom of the Upper Receiver so it stands on its own (it is always a good idea to drive punches or hammer on the side that is least visible..just in case). Use the Roll Pin Starter Punch to do this as it makes the job MUCH easier!
5. AR-15 Forward Assist Assembly Insert the Forward Assist Assembly, make sure the pawl is oriented toward the middle of the receiver

*NOTE: If you take off the spring, you can see a flat side on the Forward Assist - this is where the pin rides.
6. AR-15 Forward Assist Assembly and Upper Receiver. Slide the Forward Assist Assembly into the Upper Receiver.
7. AR-15 Forward Assist Assembly While compressing the Forward Assist Assembly, drive the pin through until it is flush with the receiver. Once the pin is firmly started, you should not have to hold the forward assist in place and you can use a large brass punch to drive the pin in until it is barely sticking up. If you find this too awkward, you can use a small punch as a slave pin to keep the Forward Assist Assembly compressed so you can use both hands. You may have to take a small punch and drive the pin a bit further until it is flush or even slightly recessed (just look at both sides to try and center the pin in the Upper Receiver)
8. AR-15 Forward Assist Assembly Test the Forward Assist to make sure it moves freely in and out when compressed.

Forward Assist Assembly is now installed.
Install Ejection Port Cover Assembly on Upper Receiver
1. AR-15 Ejection Port Assembly This assembly consists of:
  • Ejection Port Cover
  • Ejection Port Cover Pin
  • Ejection Port Cover Pin Snap Ring
  • Ejection Port Cover Spring.
2. AR-15 Ejection Port Cover Pin Snap Ring and Ejection Port Cover Pin Carefully place Ejection Port Cover Pin Snap Ring in the groove on the end of the Ejection Port Cover Pin.
3. AR-15 Ejection Port Cover Pin Snap Ring and Ejection Port Cover Pin Gently hammer Ejection Port Cover Pin Snap Ring the rest of the way onto the Ejection Port Cover Pin. Be sure to make a direct, downward strike on the snap ring. If you hit it off center, the Ejection Port Cover Pin Snap Ring may fly across the room. This is also a good time to check and make sure your safety glasses are still on.
4. AR-15 Upper Receiver Lay the Upper Receiver on its side so the Ejection Port is facing up and the Barrel Threads are pointing to the right as you stand over the Upper Receiver. Barely start the Ejection Cover Pin so it stays in place on its own, making sure the end without the snap ring is started first.
5. Ejection Port Cover Pin and AR-15 Upper Receiver Place the Ejection Port Cover on the Upper Receiver in the open position, msure the holes in Ejection Port Cover are lined up with the holes on the Upper Receiver.
6. AR-15 Upper Slide the Ejection Port Cover Pin through the hole in the Upper Receiver that is closest to the Barrel Threads, stopping just before the pin emerges in the middle opening of the Ejection Port Cover (this is where the Ejection Port Cover Spring goes).
7. AR-15 Ejection Port Cover Spring While Holding the Ejection Port Cover Spring in your left hand (by the end with the short part of the spring sticking out), grab the long part of the spring that sticks out and wind it 1/2 revolution away from your body, stopping when the long part of the spring is pointing toward you.
8. AR-15 Upper Receiver As you hold the spring under tension, place the long end on the right side of the Ejection Port Cover (closest to the Ejection Port Cover Pin that is part way through the assembly), while still holding on with your left hand, and slide the Ejection Port Cover Pin the rest of the way through, until the Ejection Port Cover Pin Snap Ring stops your progress.
9. AR-15 Upper Receiver Close the Ejection Port Cover, making sure it snaps shut.
10. AR-15 Upper Receiver Reach inside the Upper Receiver and push the Ejection Port Cover, making sure it snaps open.

Ejection Port Assembly is now installed.
Assemble the Bolt Carrier Assembly

The Bolt Carrier Assembly consists of:

  • Bolt
  • Bolt Carrier
  • Bolt Cam Pin
  • Firing Pin
  • Firing Pin Retaining Pin
AR-15 Bolt Assembly
1. AR-15 Bolt *Note: The Bolt is complete and ready to be installed in the Bolt Carrier. The Shilen Barrel we selected is Match quality and the manufacturer headspaces and numbers the Bolt (included with the barrel) to each Barrel.
2. AR-15 Bolt Carrier Push the bolt all the way into the end of the Bolt Carrier; making sure the hole through the middle of the bolt aligned with the holedirectly under the BoltCarrier Key (hollowtube that is attachby two screws to theBolt Carrier). Masure the bolt is positioned so that theextractor is on the left side of the bolt when looking at the bolt face.
3. AR-15 Bolt Cam Pin and Bolt Carrier Insert the Bolt Cam Pin through the large hole in the Bolt Carrier (just under Bolt Carrier Key). The holes in the Bolt Cam Pin will need to be perpendicular to the Bolt Carrier Key in order for the Bolt Cam Pin to clear the Bolt Carrier Key for insertion. If the Bolt Cam Pin will not go into the bolt, check the bolt orientation, as it may need to be rotated 180 degrees. Once the Bolt Cam Pin is inserted, rotate the Bolt Cam Pin 1/4 turn so the large holes in the Bolt Cam Pin are lined up with the front and back of the Bolt Carrier and the Firing Pin can slide through.
4. AR-15 Firing Pin and Bolt Carrier Slide the Firing Pin through the Bolt Carrier (toward the Bolt) until it stops.
5. AR-15 Bolt Carrier and Firing Pin Retaining Pin Insert the Firing Pin Retaining Pin through the Bolt Carrier making sure the round end of the pin is nestled all the way into the large recessed side of the Bolt Carrier. Since the Bolt Carrier is hollow, the Firing Pin Retaining Pin needs to go through the hollow part of the inside of the Bolt Carrier and enter the hole on the other side before it emerges on the other side. It can be a little tricky to achieve this alignment and pounding on the pin will not help. Once in proper alignment, this pin should slide in easily.

Test the bolt to make sure it moves in and out of the Bolt Carrier freely.

AR-15 Bolt Carrier Assembly

AR-15 Bolt Carrier Assembly is now Complete.

Assemble the Charging Handle Assembly
1. AR-15 Charging Handle Assembly The Charging Handle Assembly consists of
  • Charging Handle
  • Charging Handle Latch Spring
  • Charging Handle Latch Roll Pin
  • Charging Handle Latch
2. AR-15 Charging Handle Insert Charging Handle Latch Spring into Charging Handle.
3. AR-15 Charging Handle Start the Charging Handle Latch Roll Pin into the top of the Charging Handle so it stands on its own Use the Roll Pin Starter Punch to do this as it makes the job MUCH easier!
4. AR-15 Charging Handle While compressing the Charging Handle Latch into the Charging Handle, line up the holes and drive the Charging Handle Latch Roll Pin until it is flush.
5. AR-15 Charging Handle AR-15 Charging Handle is now completed
Install Charging Handle Assembly & Bolt Carrier Assembly into Upper Receiver

To complete the assembly of the Upper Receiver, you can go ahead and install these parts to ensure proper fit. However, you will have to remove these parts to continue with the installation of the Barrel Assembly.

1. AR-15 Upper Receiver Turn the Upper Receiver upside down so that the Picatinny rail is against the work surface. Insert the Charging Handle Assembly by lining up the tabs on the Charging Handle with the grooves inside the Upper Receiver.

Slide the Charging Handle Assembly in only far enough that it will stay stationary on its own.
2. AR-15 Bolt Carrier Assembly Pull Bolt out of Bolt Carrier as far as it will go so the Bolt Cam Pin will not contact the inside of the Upper Receiver. The Bolt Carrier Assembly will not go into the Upper Receiver if the Bolt is not pulled out.
3. AR-15 Bolt Carrier Assembly and Charging Handle Assembly Insert the Bolt Carrier Assembly (with the bolt face pointing toward the barrel threads) into the Charging Handle Assembly so that the Bolt Carrier Key rides in the trough on the underside of the Charging Handle, stopping when the Bolt Carrier Assembly and the Charging Handle Assembly are parallel and even with each other.

Push the Bolt Carrier Assembly and Charging Handle Assembly into the Upper Receiver until they click firmly into place. The Ejection Port Assembly should pop open.

AR-15 Upper Receiver
Installing the Upper Receiver into the Action Block and tightening it in the Vise
1. AR-15 Upper Receiver Remove the Charging Handle and Bolt Carrier Assembly from the Upper Receiver.
2. AR-15 Upper Receiver Slide the Action Block Insert into the back of the Upper Receiver. When you do this the Ejection Port Cover will pop open. This insert keeps the Upper Receiver from being crushed when you tighten it into the Vise.
3. AR-15 Ejection Port Cover Close the Ejection Port Cover.
4. AR-15 Upper Receiver and Action Block Place the Upper Receiver into th Action Block.
5. AR-15 Action Block Close Action Block.
6. AR-15 Action Block and Vise Place the Action Block into your Vise and tighten until snug-but do not over-tighten.
Install the Barrel
1. AR-15 Barrel and Upper Receiver Slide the Barrel into the threaded end of the Upper Receiver. Make sure the pin on the Barrel lines up with the slot in the Upper Receiver. Slide Barrel all the way into the Upper Receiver until the pin hits the back of the slot.
Install Outer Receiver Nut and Inner Barrel Retainer Nut on Barrel Threads

*Note that these instructions are recommended by the manufacturer of the Free Float Tube Handguard that we chose. If you are installing another type of handguard, instructions may vary.


1. Outer Receiver Nut and Inner Barrel Retainer Nut This assembly consists of:
  • Outer Receiver Nut
  • Inner Barrel Retainer Nut
  • Free Float Tube Handguard
  • Flat Head Handguard Screws (7)
  • Handguard Plug Screws (7)
  • Sling Swivel Studs (2)
2. AR-15 Barrel Remove Coating from the threads of the Barrel with a Steel Brush.
3. AR-15 Inner Barrel Retainer Nut and Outer Receiver Nut Remove Outer Receiver Nut and Inner Barrel Retainer Nut from Free Float Tube Handguard.

Unscrew and seperate the Inner Barrel Retainer Nut from the Outer Receiver Nut.
4. AR-15 Barrel Threads Coat barrel threads lightly with anti-seize or white lithium grease to keep the threads from galling.
5. AR-15 Outer Receiver Nut Thread Outer Receiver Nut on Barrel Threads until the Outer Receiver Nut comes in contact with the Ejection Port Cover Pin.

Unscrew the Outer Receiver Nut past one full rotation, stopping when the gas hole on the Outer Receiver Nut is lined up with the gas hole on the Upper Receiver.

6. AR-15 Inner Barrel Retainer Nut Coat Inner Barrel Retainer Nut threads lightly with anti-seize grease or white lithium grease to keep the threads from galling.
7. AR-15 Outer Receiver Nut and Inner Barrel Retainer Nut While holding the Outer Receiver Nut with one hand to keep the gas holes in alignment, thread on Inner Barrel Retainer Nut and hand tighten.
8. AR-15 Upper Receiver Please note that the manufacturer of the Free Float Handguard Tube we chose recommends that you coat the Upper Receiver Threads with Loctite and let it sit over night so the gas hoes stay in alignment when you install the Inner Barrel Retainer Nut. We skipped this step, as it will permanently install the Outer Receiver Nut. We were able to hold the other Receiver Nut in place while tightening the Inner Barrel Retainer Nut. If you are not able to do this, Loctite will be necessary.

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9. AR-15 Inner Barrel Retainer Nut and Takedown Wrench Attach Takedown Wrench to the Inner Barrel Retainer Nut, making sure at least two of the pegs on the wrench are firmly inserted into the gas tube grooves on the Inner Barrel Retainer Nut

Tighten Inner Barrel Retainer Nut with Takedown Wrench until snug. Do not over tighten. If you are not using Loctite, make sure you hold onto the Outer Receiver Nut so the gas holes stay in alignment.
10. AR-15 Torque Wrench and Takedown Wrench Install Torque Wrench into slot in the Takedown Wrench.

Seat the Threads (recommended in the U.S. Marine Corps Technical Manual). If you are not using Loctite, make sure you hold onto the Outer Receiver Nut so the gas holes stay in alignment.

  1. Torque to 35 ft-lbs
  2. Loosen
  3. Torque to 35 ft-lbs
  4. Loosen
  5. Torque past 35 ft-lbs until gas holes are in alignment, making sure not to exceed 80 lbs.

NOTE: With this particular handguard, if you cannot line up the gas holes within the torque range of 35-80 ft-lbs, loosen the Inner Barrel Retainer Nut and loosen the Outer Receiver Nut another full revolution and try again. You cannot do this if you used Loctite.

11. AR-15 Gas Tube Check to make sure Gas Tube slides freely through gas holes.

Remove Upper Assembly from Vise and Action Block.
Installing the AR-15 Gas Tube and Gas Block

This assembly consists of:

  • Gas Tube
  • Gas Block
  • Gas Tube Roll Pin.
AR-15 Gas Tube, Gas Block and Gas Tube Roll Pin
1. AR-15 Inner Barrel Retainer Nut, Outer Receiver Nut and Upper Receiver Insert Gas Tube into gas holes on Inner Barrel Retainer Nut, Outer Receiver Nut and Upper Receiver. Make sure the end with the three holes (these are for the Gas Tube Roll Pin and gas hole going into Barrel) is on the end where the Gas Block will be.
2. AR-15 Gas Block Loosen set screws on the bottom of Gas Block so it will slide over Barrel.
3. AR-15 Gas Block Slide Gas Block all the way onto Barrel as far as it will go, guiding Gas Tube into hole in Gas Block.

*Note: You may have to polish the Barrel where the Gas Block goes and polish the inside of the Gas Block with 600 grit paper so it easily slides in place. This only takes a minute or two.
4. AR-15 Gas Block Barely tighten set screws on the Gas Block so it will stay in place, but you can still rotate it by hand.
5. AR-15 Gas Block and Gas Tube Orient the Gas Block so the gas hole in the Gas Tube and the gas hole in the Barrel are perfectly aligned.

Tighten set screws.

Drive Gas Tube Roll Pin through Gas Block and Gas Tube.
Install AR-15 Free Float Tube Handguard.
1. AR-15 Free Float Tube Handguard Install 6-32 x 1/8 " Plug Screws (7) in the top of the Free Float Tube Handguard.
2. Installing AR-15 Sling Swivel Studs into Free Float Tube Handguard Install Sling Swivel Studs into Free Float Tube Handguard. To do this, remove Sling Swivel Stud from retainer nut. Place the Retainer Nut inside the Free Float Tube Handguard track. Screw Sling Swivel Stud into retainer nut.
3. AR-15 Upper Receiver Assembly Line up screw holes in Free Float Tube Handguard with the screw holes in the Outer Receiver Nut and install 6-32 x 5/16" Flat Head Screws (7).

AR-15 Upper Receiver Assembly is now ready to be attached to your Lower Receiver Assembly.

AR-15 Upper Receiver Assembly
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