AR Basics: Barrel Length and Bullet Trajectories

Published on December 4, 2025
Duration: 2:12

This video from Louisiana Firearms, featuring Gabe, explores the impact of AR-15 barrel length on bullet velocity and trajectory. It highlights how shorter barrels (e.g., 10.3 inches) are optimal for Close Quarters Battle (CQB) and confined spaces, while longer barrels (e.g., 20 inches) maximize velocity for 5.56 rounds. The discussion also covers how Bullet Drop Compensator (BDC) optics are calibrated based on these factors and the environment.

Quick Summary

For Close Quarters Battle (CQB) and clearing rooms, a 10.3-inch barrel AR-15 is considered optimal. This shorter length enhances maneuverability in confined spaces and reduces the likelihood of the firearm snagging on obstacles like doorways. Barrel length also significantly impacts 5.56 velocity, with a 10.3" barrel yielding around 2500 fps versus 3100 fps from a 20" barrel.

Chapters

  1. 00:00Optimal Build for CQB
  2. 00:13Velocity and Barrel Length Comparison
  3. 00:43BDC Optics and Trajectory Explained
  4. 01:10Environmental Considerations for Barrel Length

Frequently Asked Questions

What is the optimal AR-15 barrel length for CQB?

For Close Quarters Battle (CQB) and clearing rooms, a 10.3-inch barrel AR-15 is considered optimal. This shorter length enhances maneuverability in confined spaces and reduces the likelihood of the firearm snagging on obstacles like doorways.

How does barrel length affect 5.56 bullet velocity?

Barrel length significantly impacts 5.56 velocity. A longer 20-inch barrel allows for a full powder burn, achieving around 3100 fps. In contrast, a shorter 10.3-inch barrel limits powder burn, reducing velocity to approximately 2500 fps.

What is a Bullet Drop Compensator (BDC) and how does barrel length relate?

A BDC reticle in optics like the Trijicon ACOG is designed to compensate for bullet drop at various distances. Its accuracy depends on being calibrated to the specific trajectory of a given load, which is heavily influenced by the muzzle velocity determined by the firearm's barrel length.

When should I choose a shorter vs. longer AR-15 barrel?

Choose a shorter barrel (e.g., 10.3") for urban environments or CQB scenarios where maneuverability is key (effective range ~100-200m). Opt for a longer barrel (e.g., 20") for open terrain where maximizing velocity and range (effective range ~500-600m) is crucial for maintaining accuracy with BDC optics.

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