Hand fitting an undersized Bushmaster Magazine Well

Published on March 8, 2020
Duration: 3:11

This video details the process of hand-fitting an undersized Bushmaster AR-15 magazine well that caused magazines to stick. After approximately three hours of careful file work, the instructor was able to enlarge the magazine well sufficiently for most magazines to drop free, even though it did not meet USGI gauge specifications. The process emphasizes iterative testing with various magazines to achieve reliable function.

Quick Summary

An undersized AR-15 magazine well can cause magazines to stick, requiring manual force for removal. Fixing this involves carefully filing the interior of the well to enlarge the opening. The primary functional test is ensuring various magazines drop free, even if a USGI gauge doesn't pass.

Chapters

  1. 00:00Introduction and Problem Identification
  2. 00:10Bushmaster Lower with Sticking Magazines
  3. 00:21Undersized Magazine Well Issues
  4. 00:37Magazine Fitment Problems
  5. 00:47File Fitting Process
  6. 00:54Magazine Well Gauge Test
  7. 01:13Final Magazine Drop Test
  8. 01:20Testing Various Magazines
  9. 02:10Visual Inspection of Modified Magwell
  10. 02:46Acceptable Tight Magazine Well Achieved
  11. 02:57Conclusion and Junior Armorer Certificate

Frequently Asked Questions

What causes magazines to stick in an AR-15 lower receiver?

Magazines can stick in an AR-15 lower receiver if the magazine well is undersized, poorly broached, or has high spots internally. This can prevent magazines from seating correctly or dropping free after the release is pressed, often requiring manual force.

How can I fix an undersized AR-15 magazine well?

An undersized AR-15 magazine well can be fixed by carefully filing the interior surfaces to enlarge the opening. This is a gunsmithing task that requires patience and iterative testing with various magazines to ensure a reliable drop-free function.

Does a magazine well need to pass a USGI gauge to function correctly?

Not necessarily. While a USGI gauge is a good indicator, the ultimate test of a functional magazine well is whether a variety of common magazines drop free reliably. Some tight, but functional, magazine wells may not pass a gauge.

How long does it take to file fit an undersized AR-15 magazine well?

The time required to file fit an undersized AR-15 magazine well can vary significantly. For a severely undersized example, it can take several hours of careful, meticulous work to achieve the desired fit and function.

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