Are all AR-15 barrels threaded 1/2x28?
No — most 5.56 ones are, but .300 Blackout barrels on the same platform are usually 5/8x24. Measure or check the maker before ordering.
1/2x28 is the standard for .223 Remington and 5.56 NATO, and that covers most AR-15 barrels sold. It is a strong convention rather than a property of the platform, and the exceptions sit on rifles that look identical from the outside.
The one that catches people is .300 Blackout. It runs a 5.56-size upper — same bolt, same magazines — but the muzzle follows the .30-calibre convention at 5/8x24. Buying a muzzle device for "my AR-15" is exactly how the wrong thread pitch arrives in the post.
| .223 / 5.56 | 1/2x28, near-universally |
|---|---|
| .300 Blackout | Usually 5/8x24, occasionally 1/2x28 |
| Large-frame .308 | 5/8x24 |
| The reliable move | Check the maker’s spec for your barrel |
Caution: Thread pitch cannot be judged by eye, and a barrel that came threaded from a manufacturer is the one to ask about rather than measure badly. Where a barrel’s history is unknown, a thread pitch gauge costs less than a muzzle device.
Sources
- AR-15 thread pitch — the common pitches and what they sit on
- Common barrel thread patterns — 5/8x24 on .300 Blackout
Last checked 2026-09-03. Specifications change between production runs — verify anything safety-critical against your own firearm and the manufacturer before acting on it.
More on barrels and muzzle devices
See every answerHave a different question?
Ask TactGPT directly and get an answer written for your specific firearm and setup.
Ask TactGPT