What is a Floating Firing Pin?

Published on April 15, 2025
Duration: 6:50

This video explains the phenomenon of light primer strikes in AR-style firearms, attributing it to the design of the floating firing pin. The instructor demonstrates how a floating firing pin can leave a dimple on a primer even without a full ignition, which is normal for many AR-15 and AR-10 platforms. He also notes that the sound of the firing pin moving freely within the bolt carrier group can be an indicator of a clean firearm.

Quick Summary

A dimple on an AR-15 cartridge primer is often caused by the firearm's floating firing pin. This pin moves freely within the bolt carrier group and can strike the primer with enough force to leave a mark when the bolt is cycled, even if the firearm doesn't fire. This is a normal characteristic of most AR-15 and AR-10 platforms.

Chapters

  1. 00:02Introduction to Floating Firing Pins
  2. 00:37Firearm Assortment for Demonstration
  3. 01:15Demonstrating Primer Dimple on First Round
  4. 02:14Second Round Demonstration: Primer Dimple
  5. 03:01Third Round Demonstration: Piston CMMG
  6. 03:45Fourth Round Demonstration: Descent 5.56
  7. 04:407.62x39mm Demonstration: Mark 47
  8. 05:36Disassembling Bolt for Sound Demonstration
  9. 05:52Hearing the Floating Firing Pin
  10. 06:23Byproduct of AR-15 Design
  11. 06:27Comparison to Blowback Systems
  12. 06:40Conclusion on Floating Firing Pins

Frequently Asked Questions

What causes a dimple on a cartridge primer in an AR-15?

A dimple on an AR-15 cartridge primer is often caused by the firearm's floating firing pin. This pin moves freely within the bolt carrier group and can strike the primer with enough force to leave a mark when the bolt is cycled, even if the firearm doesn't fire.

Is a dimple on a primer a sign of a faulty AR-15?

No, a light dimple on a primer is typically not a sign of a faulty AR-15. It's a normal characteristic of firearms with a floating firing pin design, common in most AR-15 and AR-10 platforms, and indicates the firing pin is functioning as designed.

How can I tell if my AR-15 needs cleaning based on the firing pin?

You can often tell if your AR-15 needs cleaning by listening to the firing pin. When the bolt carrier group is manipulated, a clean firing pin will rattle freely. If you don't hear this sound, it suggests gunk or fouling is impeding its movement, indicating a need for cleaning.

What is the difference between a primer dimple and a light primer strike?

A primer dimple is a normal mark left by a floating firing pin when the bolt cycles. A light primer strike is a malfunction where the firing pin doesn't hit the primer hard enough to ignite the primer compound, resulting in a failure to fire.

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