THE AR FILES | Choosing Barrel Twist and why WE SHOOT the 1:7

Published on October 26, 2023
Duration: 9:27

This expert guide from 9-Hole Reviews delves into the critical aspect of barrel twist rate for 5.56 AR-15 platforms. It explains how twist rate stabilizes projectiles, the evolution of 5.56 ammunition necessitating faster twists, and the practical implications of choosing between rates like 1:7, 1:8, and 1:9 for various bullet weights and intended uses. The video emphasizes the 1:7 twist's broad compatibility and effectiveness, particularly with heavier match projectiles at extended distances.

Quick Summary

For 5.56 AR-15s, barrel twist rate is critical for bullet stabilization. A faster twist, like 1:7, is necessary for longer, heavier projectiles to prevent wobble and ensure accuracy at distance. While 1:8 and 1:9 are also common, 1:7 offers the broadest compatibility, especially with match-grade ammunition.

Chapters

  1. 00:26Introduction to Barrel Twist Rate
  2. 00:55Bullet Flight & Stabilization Explained
  3. 01:25Understanding Twist Rate: What is 1:7?
  4. 02:04Faster vs. Slower Twist Rates
  5. 02:20Evolution of 5.56 Projectiles
  6. 02:44Projectile Length & Twist Rate Rule
  7. 03:00Historical Twist Rates: M16 to M16A2
  8. 03:59Debate on Optimal Stabilization & Terminal Effect
  9. 04:43Practical Application: Twist Rates for 5.56 Ammo
  10. 05:26Impact of Over-Stabilization
  11. 06:18Consequences of Under-Stabilization
  12. 06:39Why 1:7 Twist is Preferred for Most Users
  13. 07:29Conclusion: 1:7 for Broad Compatibility

Frequently Asked Questions

What is barrel twist rate and why is it important for AR-15s?

Barrel twist rate refers to the rifling inside the barrel that spins a bullet for stabilization. For 5.56 AR-15s, the correct twist rate, like 1:7, is crucial for stabilizing projectiles, especially heavier ones, ensuring accuracy at distance and preventing wobble or yaw.

How does projectile weight affect the required barrel twist rate for 5.56 NATO?

Longer and heavier projectiles require a faster twist rate to stabilize them. For example, 5.56 ammunition has evolved to heavier bullets, necessitating faster twists like 1:7, compared to older, lighter bullets that could be stabilized by slower twists like 1:12 or 1:14.

What are the common barrel twist rates for 5.56 AR-15s and their optimal bullet weights?

Common rates include 1:9 (optimized for 45-69gr), 1:8 (optimized for 55-77gr), and 1:7 (optimized for 62-77+gr). The 1:7 twist is often preferred for its versatility with heavier match-grade ammunition.

What happens if an AR-15 barrel's twist rate is too slow for the bullet?

If the twist rate is too slow (under-stabilization), the bullet will not spin sufficiently. This leads to a dramatic loss of accuracy, keyhole impacts on targets, and in severe cases, the bullet jacket can rip apart in flight.

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