Quick Tip: Converting a 5.56 AR-15 to 9mm

Published on April 23, 2019
Duration: 4:19

This guide details the process of converting a 5.56mm AR-15 to fire 9mm ammunition, a modification that shifts the firearm's operation from gas-operated to straight blowback. The conversion requires specific components like a 9mm barrel, bolt, and buffer, along with a magazine adapter. Instruction is provided by a Brownells technical expert, emphasizing the mechanical differences and necessary parts.

Quick Summary

Converting a 5.56 AR-15 to 9mm involves changing the operation from gas-operated to straight blowback. This requires a dedicated 9mm barrel (lacking gas components), a heavier 9mm bolt, a heavy 9mm buffer, and a magazine adapter (like Stern Defense for Glock or Hahn Precision for Colt magazines). Ensure correct muzzle threading and avoid using 5.56mm muzzle devices.

Chapters

  1. 00:00Introduction to 9mm AR-15 Conversion
  2. 00:14Barrel Differences
  3. 00:40Bolt and Buffer Requirements
  4. 01:40Muzzle Devices
  5. 02:12Magazine Adapters

Frequently Asked Questions

What are the main differences between a 5.56mm AR-15 barrel and a 9mm AR-15 barrel for conversion?

A 9mm AR-15 barrel for conversion operates on a straight blowback system, meaning it lacks the locking lug recesses found on 5.56mm barrels. It also does not require a gas port, gas block, or gas tube, simplifying the upper receiver assembly.

Why is a heavier bolt and buffer necessary for a 9mm AR-15 conversion?

A heavier 9mm bolt and a dedicated heavy 9mm buffer are crucial for straight blowback operation. They ensure the action remains securely closed during firing, managing the increased bolt thrust inherent in blowback systems and preventing premature extraction.

What types of magazine adapters are available for 9mm AR-15 conversions?

Two common types of magazine adapters are discussed: Stern Defense, which allows the use of Glock magazines, and Hahn Precision, designed for Colt-style 9mm magazines. The choice depends on magazine availability and user preference.

Can I use a 5.56mm muzzle device on a 9mm AR-15 barrel?

While some thread pitches may match (e.g., 1/2-28), it is unsafe to use a 5.56mm muzzle device on a 9mm barrel. The bore diameter of a 5.56mm device is too small for 9mm projectiles, creating a risk of baffle strikes or obstruction.

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