Smyth Busters: AR-15 Small Parts Kits Are NOT All the Same

Published on November 16, 2021
Duration: 5:16

This guide, based on expert insights from Brownells and Sons of Liberty Gun Works, details the critical aspects of selecting and inspecting AR-15 lower parts kit components. It emphasizes that material quality, proper heat treatment, and precise manufacturing tolerances for parts like springs, detents, and fire control groups are crucial for rifle reliability and longevity. Proper inspection prevents common assembly issues and ensures optimal firearm function.

Quick Summary

AR-15 small parts kits are not interchangeable in quality. Experts highlight that critical components like 17-7 Stainless Steel springs and cadmium-coated detents are crucial for reliability. Variations in fire control group finishing and trigger pull weights (5.5-9.0 lbs for mil-spec) also differentiate kits, with premium brands offering more consistent performance.

Chapters

  1. 00:00Introduction: AR-15 Small Parts Kits Aren't Equal
  2. 00:55Spring Materials: 17-7 vs. 302/303 Stainless
  3. 01:10Fire Control Group: Trigger Pull Weight & Reset
  4. 01:55Detents & Bolt Catches: Material Importance
  5. 03:24Pins & Quality Control: Avoiding Common Mistakes

Frequently Asked Questions

Why are AR-15 small parts kits not all the same?

AR-15 small parts kits differ significantly in the quality of their components. Factors like the material used for springs (17-7 Stainless Steel is preferred), the coating on detents (cadmium preferred), and the manufacturing tolerances of fire control group parts directly impact the rifle's reliability and longevity.

What are the key components to inspect in an AR-15 lower parts kit?

Key components to inspect include springs (material and heat treatment), detents (coating and material), fire control group parts (finish and engagement surfaces), and pins (correct sizing). Reputable brands like BCM and Sionics often offer superior quality in these small but critical parts.

What is the importance of spring material in an AR-15 lower parts kit?

Spring material is critical for reliability. 17-7 Stainless Steel springs are preferred because they can be properly heat-treated, offering superior longevity and consistent performance compared to 302 or 303 stainless steel, which cannot achieve the same level of durability.

How do trigger pull weights vary in AR-15 'mil-spec' kits?

Even 'mil-spec' triggers can have pull weights ranging from 5.5 to 9.0 lbs. High-quality manufacturers often refine these triggers to achieve a more consistent and desirable pull, typically around 6 lbs, with a positive reset, enhancing the shooting experience.

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