Criterion Barrels: 12.5" Barreled Upper Receiver

Published on August 26, 2019
Duration: 15:20

This video details a custom 12.5-inch AR-15 upper receiver build by Criterion Barrels, focusing on optimizing timing and reliability. Key improvements include truing the receiver face, upgrading to a full-mass BCG, and recommending an H3 buffer to manage dwell time. Accuracy testing demonstrated sub-MOA potential, with a best group of 0.75 inches.

Quick Summary

Criterion recommends an H3 buffer (approx. 5.6 oz) for their 12.5" barreled upper to improve timing and reduce wear. This allows the bolt to remain locked longer, letting chamber pressures subside before extraction, leading to smoother operation and better reliability, especially when suppressed.

Chapters

  1. 00:00Introduction & Project Background
  2. 02:09Technical Analysis: Dwell Time & Timing
  3. 05:41System Optimization Recommendations
  4. 06:05Receiver Truing & Component Upgrades
  5. 09:26Field Testing & Suppressor Performance
  6. 10:31Accuracy Testing Results

Frequently Asked Questions

What buffer weight is recommended for the Criterion 12.5" barreled upper receiver?

Criterion recommends increasing the buffer weight to at least an H3 (approximately 5.6 oz) to improve timing and reduce wear. This helps keep the bolt locked longer, allowing chamber pressures to subside before extraction.

What modifications were made to optimize the AR-15 upper receiver's reliability?

The upper receiver face was trued, a lightened BCG was replaced with a full-mass Mil-Spec BCG and BCM bolt, and a timing-independent BCM rail was installed. These changes optimize system inertia and reduce wear.

What accuracy was achieved with the Criterion 12.5" barrel?

Accuracy testing at 100 yards showed varied results by ammunition. The best group achieved was 0.75 inches using Minuteman Munitions 68gr BTHP ammunition, with Hornady Black 62gr yielding 1.2" and Fiocchi 69gr yielding 1.7".

How does dwell time affect AR-15 reliability?

Locked bolt dwell time is critical. A longer dwell time allows chamber pressures to decrease significantly before the bolt unlocks and extracts the spent casing. This reduces stress on components and prevents extraction issues, especially with suppressed fire.

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