Bolt Carrier Group(BCG)

Among all the parts of the AR-15, the Bolt Carrier Assembly is the most significant part. Its primary purpose is to help in the functioning of the semi-automatic mechanism while firing. The Bolt Carrier Assembly comes as a complete component or separate parts you can easily assemble.

Regardless of its form, it’s vital a shooter knows how to assemble the Bolt Carrier Assembly since it’s this part that requires frequent cleaning in an AR-15. This article reflects on the individual parts and tools needed to assemble the Bolt Carrier Assembly and a step-by-step guide on how to assemble.

Parts Of The Bolt Carrier Assembly Needed

  • AR-15 Bolt Carrier 
  • AR-15 Bolt 
  • Extractor 
  • Extractor Pin 
  • Extractor Spring
  • Extractor insert 
  • Ejector 
  • Ejector Roll Pin 
  • Bolt Gas Rings 
  • Bolt Cam Pin 
  • Firing pin Retaining Pin 
  • Firing Pin

Tools Needed 

  • Allen Wrenches 
  • Punch set 
  • Needle-Nose pliers 
  • Brass/Nylon Hammer 
  • AR-15 Vise Block 

Step by Step Guide on How to Assemble Bolt Carrier Group (BCG)

How To Assemble A Bolt Carrier Group

How To Assemble A Bolt Carrier Group

  • The first thing will involve installing the Ejector into your AR-15 Bolt. Start by setting the Bolt on to the Vise Block and fix the Ejector Spring into the Ejector hole. Then use the Punch Set Roller to prestart the hole for the Roll Pin. Proceed and use a Punch and the hammer to push down the Ejector. Finally, completely drill in the Roll pin using your Punch. Make sure the Ejector moves freely.
  • Install the Extractor Spring and Insert into the Extractor.
  • The larger side of the Extractor Spring should go into the Extractor.
  • Use Needle-Nose to apply pressure onto the spring slightly. Then install your Extractor into the Bolt. 
  • You also need to install your Gas Rings. Use your hands and ensure they are gapped evenly. 
  • Now you have an assembled Bolt.
  • Insert the Bolt into the Bolt Carrier. If the Bolt is facing you, the extractor should be on the right-hand side. As you fix it in, you will feel the gas rings. Also, ensure the large opening of the Bolt correctly aligns with the Bolt Carrier opening. 
  • Drop in the Bolt Cam Pin through an opening on the Bolt Carrier into the Bolt. Pull back the Bolt and turn the Cam Pin 90 degrees.
  •  Hold the Bolt Carrier upside down with the gas key facing the table. Insert the Firing Pin and tap it with your Punch to ensure it goes all the way down. 
  • The next thing will be to insert the Firing Pin Retaining Pin from the same side of the Bolt Carrier you put in the Cam Pin. 
  • Now you have complete Bolt Carrier Assembly 
  • You may install the assembly into your Upper Receiver. 


As mentioned earlier, the Bolt Carrier Assembly is a crucial part of an AR-15 and its overall functioning. Therefore, every shooter ought to learn and practice assembling and to disassemble the Bolt Carrier Group. You will not have a hard time cleaning your AR-15 and checking it in case it is not firing.

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