Can More Be Less? CORBON .223 77gr MPR (TMK) 20" Barrel Gel Test

Published on November 29, 2019
Duration: 6:54

This video tests the CORBON .223 77gr Sierra TMK (Tipped Match King) from a 20-inch AR-15 barrel into ballistic gelatin. Contrary to the common misconception that higher velocity always means deeper penetration, the test reveals that the increased velocity from the 20-inch barrel caused the TMK bullet to fragment excessively, resulting in shallower penetration (9.5 inches) compared to its performance from a shorter barrel. The instructor recommends this bullet for shorter barrels in home defense scenarios where over-penetration is a concern, but advises against it for longer barrels due to its fragility at higher velocities. For longer barrels or situations requiring barrier penetration, bonded soft-point bullets like Fusion or Bear Claw are recommended.

Quick Summary

The CORBON .223 77gr Sierra TMK bullet, while excellent from short barrels, showed reduced penetration from a 20-inch AR-15 due to excessive fragmentation at higher velocities. This highlights that increased velocity doesn't always mean deeper penetration for expanding bullets.

Chapters

  1. 00:10Intro: Sierra 77gr TMK Reputation
  2. 00:48Misconception: Velocity vs. Penetration
  3. 01:27Test Setup: 20" AR-15, CORBON 77gr TMK, Gel
  4. 02:26Test Results: Penetration and Fragmentation
  5. 02:45Analysis: 9.5" Penetration is Unacceptable
  6. 03:49Visuals: Extensive Fragmentation
  7. 04:33Learnings: Bullet Fragility at High Velocity
  8. 05:00TMK for Defense: Still Good for Short Barrels
  9. 05:35Recommendations: Bonded Soft Points for Long Barrels
  10. 06:04Outro and Support

Frequently Asked Questions

Why did the CORBON .223 77gr TMK penetrate less from a 20-inch barrel than a shorter one?

The increased velocity from the 20-inch barrel caused the Sierra 77gr TMK bullet to fragment excessively. This fragmentation leads to increased drag and mass shedding, which paradoxically reduces the bullet's overall penetration depth in ballistic gelatin.

Is the Sierra 77gr TMK still a good choice for home defense?

Yes, the Sierra 77gr TMK remains an excellent choice for home defense, particularly when used with shorter barrels. Its performance is impressive out of barrels like 10.5 inches. However, its fragility at higher velocities makes it less ideal for longer barrels.

What are recommended alternatives to the 77gr TMK for longer barrels?

For longer barrels or situations where barrier penetration is crucial, bonded soft-point bullets are recommended. Examples include 62-64 grain loads like Federal Fusion or various Bear Claw ammunition, which tend to perform more reliably through barriers and at extended ranges.

Does higher bullet velocity always mean deeper penetration?

No, this is a common misconception. While generally true for non-expanding bullets, for bullets designed to expand or fragment, higher velocities can lead to more aggressive deformation, increased drag, and mass shedding, potentially resulting in reduced penetration.

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