Quick Tip: What Is AR-15 "Dwell Time"?

Published on April 20, 2022
Duration: 7:44

This expert-level guide from Brownells explains AR-15 dwell time, a critical concept for builders and troubleshooters. Dwell time is defined as the duration gases from a fired cartridge act on the firearm's operating system, specifically the bolt carrier group. Understanding its relationship with gas system length and gas port proximity is key to diagnosing and preventing malfunctions.

Quick Summary

AR-15 dwell time is the period during which gases from a fired cartridge act upon the firearm's operating system, particularly the bolt carrier group. It's influenced by gas system length; shorter systems mean more dwell time and higher pressure, while longer systems mean less dwell time and lower pressure. Understanding this is key for building and troubleshooting.

Chapters

  1. 00:04Introduction to Dwell Time
  2. 00:41Defining Dwell Time
  3. 01:03AR-15 Components Explained
  4. 01:57Incorrect Dwell Time Definition
  5. 02:40Why Dwell Time Matters
  6. 03:24Diagnosing Issues with Ejection Pattern
  7. 03:42Measuring and Changing Dwell Time
  8. 04:08AR-15 Gas System Lengths
  9. 05:06Dwell Time and Gas Port Proximity
  10. 05:34Gas Pressure and Bullet Travel
  11. 06:33Recap of Dwell Time Definition
  12. 07:08Conclusion and Call to Action

Frequently Asked Questions

What is dwell time on an AR-15?

Dwell time on an AR-15 is the duration that gases from a fired cartridge exert pressure on the firearm's operating system, specifically the bolt carrier group. It's a critical factor in how the rifle cycles.

How does gas system length affect dwell time in an AR-15?

Shorter gas systems (pistol, carbine) have gas ports closer to the chamber, leading to longer dwell times and higher gas pressure. Longer systems (mid-length, rifle) have ports further away, resulting in shorter dwell times and lower gas pressure.

What is the correct way to diagnose AR-15 gas system issues?

The most effective way to diagnose gas-related malfunctions in an AR-15 is by observing the ejection pattern of spent casings. Consistent patterns indicate proper gas system function, while erratic patterns suggest issues.

Can you directly measure AR-15 dwell time?

No, dwell time cannot be measured with a stopwatch. It's a conceptual understanding of how long gas pressure acts on the system, influenced by factors like gas port size and gas system length, not a discrete event with a start and end time.

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