KAC Blem Lower Receiver Bolt Catch Problem & Physical turned to Autopsy

Published on December 22, 2020
Duration: 33:10

This guide details a modification procedure for repairing oversized bolt catch pin holes on an AR-15 lower receiver, specifically addressing a KAC SR-15 blemished unit. It involves drilling and tapping the holes to accept a threaded pin, a technique also seen on Aero Precision receivers. The process requires specialized tools and precise execution, as demonstrated by the School of the American Rifle, highlighting the importance of proper tooling and technique for firearm repair.

Quick Summary

Repairing oversized bolt catch pin holes on an AR-15 lower receiver involves drilling the holes with a #35 bit and tapping them for a 6-32 threaded pin. Applying Vibra-Tite VC-3 Threadmate to the pin before installation secures it. This precise gunsmithing technique, shown by the School of the American Rifle, ensures the bolt catch remains functional and stable during operation.

Chapters

  1. 00:00Introduction & Bolt Catch Issue
  2. 01:35Repair Strategy & Tooling
  3. 03:54Buffer System & BCG Gap
  4. 07:13Takedown & Pivot Pin Gauging
  5. 08:15Magazine Well Gauging
  6. 12:12Trigger & Hammer Pin Analysis
  7. 13:43Selector Bore & Removal
  8. 18:39Receiver Extension Thread Gauging

Frequently Asked Questions

How do you fix oversized bolt catch pin holes on an AR-15 lower receiver?

To fix oversized bolt catch pin holes, drill them out with a #35 bit and tap them for a 6-32 threaded pin. Apply thread locker like Vibra-Tite VC-3 before installing the pin to ensure it stays secure during operation. This method is demonstrated by the School of the American Rifle.

What are common dimensional issues found on blemished AR-15 lower receivers?

Blemished lower receivers, like the KAC SR-15 example, can exhibit oversized pin holes (bolt catch, hammer, trigger), loose receiver extension threads, undersized magazine wells, and excessive slop in pivot/takedown pin holes, requiring specific gunsmithing techniques to correct.

What tools are needed for modifying an AR-15 lower receiver with oversized bolt catch pin holes?

Essential tools include a #35 drill bit, a 6-32 H3x6" pull-through tap, a drill, Vibra-Tite VC-3 Threadmate, and precision pin gauges for verification. Safety glasses are mandatory.

Why is it important to check the BCG gap on an AR-15?

Checking the bolt carrier group (BCG) gap ensures there is sufficient clearance between the gas key and the lower receiver. Proper clearance prevents the gas key from striking the receiver during firing, which could cause damage or malfunctions. A custom gauge is often used for this measurement.

Related News

All News →

More Gunsmithing & DIY Videos You Might Like

More from School of the American Rifle

View all →