DIY AR-15 Build – Bolt Carrier Group Installation

by October 13, 2011 10/13/11
DIY AR-15 Build - Bolt Carrier Group Installation
6 of 8 in the series DIY AR-15 Build Upper

Today in our continuing DIY AR-15 Build, we’ll be assembling the Bolt Carrier Group, putting it into the Upper Receiver and talking about some different parts and myths to ensure your build finishes up without a hitch!

The Bolt Carrier Group is particularly important to not only diagnose, but to build properly with good parts right from the beginning. Many malfunctions are directly related to the Bolt Carrier Group, particularly the Extractor within the Bolt.

A BCG is made up of the Bolt Carrier, Bolt (complete), Firing Pin, Cam Pin, Firing Pin Retaining Pin and we like to lump the Charging Handle in with this, though many don’t.

Let’s get into the specifics and talk about the assembly and our recommendations.

Bolt Carrier Group

While the assembly of the BCG may seem fairly straightforward, it’s the most important group of parts on the AR-15 and likewise important that we take the time to talk about a few key areas to pay attention to. What we’re not going to get into here is the differences in the parts you may have at home on your AR-15, but what we recommend you start with from the beginning.

Maintenance and Replacement of parts is something we’ll be getting into with our next installment of our series on How to Keep your AR Running. For starters, if you follow our parts list below, you’ll see we’re using ALL Bravo Company USA parts. We feel Bravo Company offers some of the very best parts on the market, especially when it comes to the importance of the BCG.

Extractor Spring and Insert

DIY AR-15 Build - Bolt Carrier Group Installation

Of particular importance on the BCG are a properly staked Carrier Key and correct Extractor Spring with insert.

Starting with the Extractor Spring, you want a well made spring and black insert, which is exactly what Bravo Company includes with their Bolts. Their Extractor Springs are made from chrome silicon, heat treated & stress relieved and shot peened.

Failure to extract and stove pipe malfunctions can, more often than not, be traced back to a faulty extractor spring/insert combo. If your Extractor Spring is weak the Extractor won’t grab the spent round and properly extract it, resulting in a either a stuck case or one that doesn’t completely eject before the bolt comes back (stove pipe).

We’ve also mentioned the importance of High Pressure Testing and Magnetic Particle Inspection in a previous article and it definitely applies here as well. You want to ensure your bolt is HP/MP!

Carrier Key Staking

DIY AR-15 Build - Bolt Carrier Group Installation

A properly staked Carrier Key is of the upmost importance on a Direct Impingement AR. As spent gas travels back to the Gas Key on the Bolt Carrier it’s dependent on proper alignment to complete the cycle of operations. A loose carrier key can cause short stroking, or when the bolt carrier doesn’t get far enough back to be able to travel forward and strip off the next round.

Bravo Company properly stakes their keys as seen in the photo to the right. If your’s doesn’t look like this we’ll get into detail on how to do this properly in our next  How to Keep your AR Running  article.

Gas Rings

DIY AR-15 Build - Bolt Carrier Group Installation

First of all, let’s dispel the myth you might have learned in bootcamp. The gaps in the gas rings do not have to be staggered! It’s not going to hurt, but not mandatory. You should ensure there are three of them, but we’ve seen guns run with one gas ring before.

The goal of the gas rings are to trap enough gas to push the bolt carrier to the rear. A test on how to know if you need to replace the gas rings is demonstrated by Bryan in the video below.

Set the assembled BCG down on the table with the bolt face facing down. If it stands up under it’s own weight, the gas rings are good. If the Bolt Carrier drops under it’s own weight, it’s time to replace the gas rings.

Accessories and Furniture

At this point you can also slap on any accessories and furniture you might want to put on the Upper Receiver of your new AR-15. We used various Magpul goodies coated in Desert Digital by our friends at CRC Hydrographics. Everything we had coated by them, with the exception of the Back Up Iron Sight, features their new Grip-Tec coating,

We’re looking forward to evaluating the durability of the clear grippy texture further after we assemble this AR completely and get to start putting rounds through it!

Parts Needed

Tools Needed

  • Screwdriver

Assembly Instructions

  • Insert the Bolt into the Bolt Carrier with the flared side facing out
  • Turn the Bolt, aligning the larger opening with the Bolt Carrier opening just below the Carrier Key
  • Insert the Cam Pin through the Bolt Carrier opening and into the Bolt so that the flat bar on top of the Cam Pin is inline with the Bolt Carrier
  • Pull the Bolt back to extend it and turn the Cam Pin 90 degrees.
  • Drop in the Firing Pin (pointed side down) from the opposite end of the Bolt Carrier and press it down to properly seat it.
  • Insert the Firing Pin Retaining Pin in through the larger opening on the same side of the Bolt Carrier you inserted your Cam Pin from.
  • This completes the assembly of the Bolt Carrier Group.
  • Insert the Charging Handle into the proper cut out notch in the Upper Receiver
  • Ensure the Bolt is still extended within the carrier and place it into the Charging Handle with the Carrier Key providing the alignment.
  • Press everything home and listen for the audible click of the Charging Handle seating.
<----- scroll or drag ----->

Join us back here soon for the next installment in the DIY AR-15 Build (Upper Receiver) where we’ll be checking the headspace and welding the BattleComp 1.5  to complete the Upper Receiver!


Are you getting more than 14¢ of value per day from ITS Tactical?

Please consider joining our Crew Leader Membership and our growing community of supporters.

At ITS Tactical we’re working hard every day to provide different methods, ideas and knowledge that could one day save your life. Instead of simply asking for your support with donations, we’ve developed a membership to allow our readers to support what we do and allow us to give you back something in return.

For less than 14¢ a day you can help contribute directly to our content, and join our growing community of supporters who have directly influenced what we’ve been able to accomplish and where we’re headed.

Click here to learn about all the benefits and Join!


G Washington
G Washington

Clear and useful presentation. One piece of constructive criticism: Many people who are not comfortable with public speaking fall into the habit of smacking their lips or clicking their tongues after every statement...It's like an audible expression of periods and exclamation points.


Be cautious of this, because it can be both tiresome and irritating to listen to.

Delta5
Delta5

Built my first AR w/ these tutorials. Great work and much appreciated. You never mentioned any grease, oil, or lubricants. A total AR noob like myself would appreciate that very much. Thanks.

Craig Andersen
Craig Andersen

I recommend a buffer-tech extractor upgrade-bulletproof!

The Latest
Squawk Box