2 - FN Lower Receiver Physicals

Published on November 30, 2020
Duration: 7:09

This guide details the inspection process for FNHUSA FN-15 lower receivers, focusing on critical fitment checks. It covers magazine well, lug area, selector pin, take-down pin, and threaded receiver extension hole tolerances. The inspection also includes assessing hammer and trigger pin hole dimensions using various gauges to identify potential assembly issues or sensitivities to specific components.

Quick Summary

When inspecting an FNHUSA FN-15 lower receiver, focus on critical fitment areas like the magazine well using a gauge, pin holes for selector and take-down pins, and the threaded receiver extension. Check for undersized threads or tight pin holes, which can sometimes be caused by new anodizing or refinishing processes.

Chapters

  1. 00:00Introduction to FNHUSA Lower Receivers
  2. 00:14Receiver Markings and Identification
  3. 00:46Magazine Well Fitment Test
  4. 01:25Selector and Take-Down Pin Hole Checks
  5. 01:39Fire Control Group Pocket Inspection
  6. 01:47Receiver Extension Thread Inspection
  7. 02:41Hammer and Trigger Pin Hole Gauge Tests
  8. 03:41Summary of Lower Receiver Tolerances
  9. 03:59Conclusion: Building Quality Firearms

Frequently Asked Questions

What are the key areas to inspect on an FNHUSA FN-15 lower receiver?

Key inspection areas include the magazine well for proper fitment, lug areas, selector and take-down pin holes for gauge fit, the fire control group pocket for even thickness, and the threaded portion for the receiver extension. Hammer and trigger pin holes are also checked for precise dimensions.

How can I check if a lower receiver's magazine well is properly sized?

You can check the magazine well's sizing using a dedicated magazine well gauge. If the gauge is tight or doesn't pass, the receiver may be sensitive to certain magazines, potentially affecting reliability.

What issues might arise from undersized receiver extension threads on a lower receiver?

Undersized threads for the receiver extension can make it difficult to install a buffer tube. You might need to select a buffer tube with slightly looser tolerances or consider running a tap to correct the thread dimensions.

Can new anodizing affect the fitment of pins on a lower receiver?

Yes, new anodizing can sometimes cause temporary tightness in pin holes, such as for the selector or take-down pins. This tightness may resolve with use or break-in, but it's important to note during inspection.

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