How to Bed an AR-15 or AR-10 Barrel Extension into the Upper Receiver

Disclaimer

The information provided in this blog post is intended for experienced gunsmiths with advanced knowledge of firearm maintenance and modification. Bedding a barrel extension into an AR-15 or AR-10 upper receiver involves the use of specialized tools, materials, and chemicals, as well as adherence to proper safety protocols.

Redleg Guns is not responsible for any damage, injury, or legal issues resulting from the application of the techniques described herein. Firearm modifications, including barrel bedding, should be conducted in compliance with all local, state, and federal laws.

Always prioritize firearm safety and ensure all firearms are unloaded and cleared before beginning any work. Use proper protective equipment, such as gloves and eye protection, when handling hazardous materials like acetone or bedding compounds.

If you are unsure of your ability to perform these tasks safely and correctly, consult a professional gunsmith. By proceeding with the steps outlined in this guide, you acknowledge and accept all risks associated with firearm modification and assume full responsibility for the outcomes.

Barrel bedding is a precise process that enhances the fit between the barrel extension and the upper receiver of an AR-15 or AR-10. This improves the firearm’s accuracy by minimizing unwanted movement and optimizing barrel harmonics. This guide provides a detailed step-by-step explanation of how to bed an AR barrel extension using Acraglass, with insights for master-level gunsmiths.

Why Bed the Barrel Extension?

When building your own AR style rifle you usually don’t get to pick out the specs of your upper receiver or barrel extension diameters. When the fit between the barrel extension and upper receiver is loose, it can negatively affect the consistency and accuracy of your rifle. Bedding the extension creates a secure, stress-free fit that improves rigidity and stability. This process is particularly beneficial for long-range shooters and precision enthusiasts where even the smallest tolerances matter.

Tools and Materials Needed

• Vise: A vise with protective jaws for secure, scratch-free clamping.

• Bedding Compound: Acraglass liquid (preferred for its flow properties); alternatives include MarineTex or other firearm-specific epoxy bedding compounds.

• Release Agent: Kiwi shoe polish or Brownells spray-on release agent.

• Tape: Painter's or masking tape for protecting critical areas during sandblasting or sanding.

• Sandpaper: 220-grit (ideal for roughening surfaces); 150-grit blasting media if using a sandblaster.

• Acetone: For degreasing components.

• Cotton Swabs/Q-tips: For cleaning excess bedding material during the process.

• Gloves and Eye Protection: Standard safety equipment for handling acetone and bedding compounds.

• Disassembly Tools: Tools for disassembling upper receiver.

Step-by-Step Process

1. Preparation and Safety

• Set up a stable and clean workspace. Have vise with protective jaws to hold the upper receiver securely without scratching or damaging upper receiver.

• Put on gloves and eye protection to safely handle acetone and epoxy compounds.

  
  

2. Degreasing the Components

• Thoroughly clean the barrel extension and the interior of the upper receiver using acetone to remove any oil, grease, or debris. This ensures proper adhesion and prevents contamination during bedding.

  
  

  

  
  
  
  

3. Taping and Surface Preparation

• Use tape to protect the barrel and any areas where you don’t want blasting media or sandpaper to contact.

  
  

  

  
  

• If sandblasting, tape over the outside of the barrel and inside of the extension to keep blasting media out of critical areas. Use 150-grit blasting media to roughen the outer surface of the extension.

• If you don’t have a sandblaster, use 220-grit sandpaper to roughen the extension surface manually. This step is critical to create a mechanical bond between the bedding compound and the extension.

  
  

4. Cleaning and Applying Release Agent

• After roughening, clean the barrel extension and the interior of the upper receiver again with acetone.

  
  

  

  
  

• Apply release agent to the interior of the upper receiver and any areas where you don’t want the Acraglass or bedding compound you use to bond. Use Kiwi shoe polish or a spray-on release agent with even coverage. Ensure all surfaces are thoroughly coated to prevent accidental adhesion.

  
  

  

  
  
  
  

5. Mixing the Acraglass

• Mix the Acraglass liquid or bedding compound you are using according to the manufacturer’s instructions. Proper mixing is critical to ensure consistent curing and optimal bonding strength.

  
  

  

  
  
  
  

6. Applying the Bedding Compound

• Apply the Acraglass to the roughened surface of the barrel extension, ensuring an even layer without voids. We apply the bedding compound to the barrel extension because there is usually a relief cut on the barrel extension and if you attached the bedding compound to the inside of the upper receiver you wouldn’t be able to remove the barrel because it would form around the smaller diameter of the relief cut.

  
  

  

  
  
  
  

7. Inserting the Barrel into the Upper Receiver

• Carefully insert the barrel extension into the upper receiver, maintaining alignment to prevent uneven bedding.

  
  

  

  
  

• As you insert, use cotton swabs or Q-tips to remove any excess Acraglass that flows out of the receiver. Pay attention to both the interior and exterior for a clean finish.

  
  

  

  
  
  
  

  

  
  

8. Securing the Assembly

• Once the barrel is fully seated, mount the upper receiver and barrel vertically in the vise.

  
  

  

  
  

• Apply release agent to the threads of the barrel nut, then thread it onto the receiver to apply tension. The nut will hold the extension securely in place as the Acraglass cures.

  
  

  

  
  
  
  

9. Curing the Acraglass

• Allow the Acraglass to cure for the full duration specified in the instructions. Curing times may vary depending on temperature and humidity, so follow the manufacturer’s guidance for optimal results.

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10. Post-Cure Inspection

• After curing, disassemble the receiver and inspect the bedding. Check for complete and even contact between the barrel extension and receiver.

  
  

  

  
  

• Verify that there are no voids, gaps, or excess material that could interfere with the function of the firearm. If necessary, use a file or sandpaper to remove small imperfections.

• Clean up release agent or kiwi shoe polish. Reinstall barrel and all parts. Perform function check.

How Bedding Improves Accuracy

Bedding the barrel extension creates a rigid and consistent fit that eliminates movement between the barrel and upper receiver. This reduces flex during firing, stabilizes barrel harmonics, and enhances overall accuracy. For competition shooters and precision hunters, this can make a measurable difference in group size and consistency.

Common Mistakes and How to Avoid Them

1. Improper Mixing of Acraglass:

   • Always mix the compound thoroughly according to the manufacturer’s instructions to ensure proper curing.

2. Forgetting the Release Agent:

   • Failing to apply release agent will result in the barrel permanently bonding to the upper receiver, making disassembly nearly impossible.

3. Uneven Bedding Application:

   • Ensure the Acraglass is applied evenly to the barrel extension to prevent inconsistent fitment.

Are you ready to take your AR’s accuracy to the next level? Follow these steps and share your results in the comments below!

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