AR15 Bolt Carrier Group Coatings & Finishes - The Good & Bad

Published on February 27, 2023
Duration: 25:18

This guide details the analysis of AR15 Bolt Carrier Group (BCG) coatings and finishes, drawing on extensive experience from Chad Albrecht of School of the American Rifle. It categorizes finishes from best to worst based on mechanical efficiency and dimensional accuracy, highlighting common issues with each type, such as corrosion with chrome, lubrication retention with phosphate, and potential brittleness with improperly treated nitride. The assessment emphasizes how coatings affect gas sealing and component wear.

Quick Summary

Chad Albrecht of School of the American Rifle analyzes AR15 Bolt Carrier Group (BCG) finishes, ranking them by mechanical efficiency and dimensional accuracy. Top choices include Chrome, Phosphate, and NP3 for reliability. He warns against Nickel Boron due to potential wear and dimensional issues, and notes that Nitride requires precise manufacturing to avoid efficiency problems.

Chapters

  1. 00:00Introduction to BCG Finishes
  2. 00:53Chrome Finishes and Mechanical Efficiency
  3. 06:06Phosphate and NP3 Coatings
  4. 11:33DLC, Nano, and Nitride Treatments
  5. 16:06PVD and Aesthetic Coatings
  6. 17:52Nickel Boron (NiB) Issues

Frequently Asked Questions

What are the best AR15 Bolt Carrier Group (BCG) finishes for mechanical efficiency?

Based on expert analysis, Chrome, Phosphate (often with internal chrome lining), and NP3 are considered top-tier finishes for AR15 BCGs due to their mechanical efficiency and dimensional stability. These finishes contribute to better gas sealing and reliable firearm cycling.

What are the common problems with Nickel Boron (NiB) BCG coatings?

Nickel Boron coatings can cause issues like short headspace, reduced firing pin protrusion, and trapping fouling, which acts like a lapping compound wearing down the receiver. Coating buildup can also prevent proper seating of components like the carrier key.

How does Nitride treatment differ from other BCG coatings?

Nitride is a surface treatment, not a coating, meaning it doesn't add thickness. This requires manufacturers to maintain precise machining dimensions; otherwise, it can lead to oversized bores and gas leaks. Improper heat treatment can also make 9310 steel bolts brittle.

Why are PVD and Titanium Nitride (TiN) finishes often criticized for BCGs?

PVD and TiN finishes are frequently chosen for aesthetics ('bling'). However, they often exhibit rough internal surfaces and poor mechanical efficiency. Examples include bolts with damaged firing pin holes, indicating potential issues with metal softness or heat treatment.

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