MARC and MARC II
AR-15 FRD Tuning Guide
Describe your rifle. Get one buffer to start with, what to do when it runs wrong, and what has to be true before you install. Numbers come off our own test guns plus consolidated community reports. Your build may want something different.
1Platform
Also published:
Running but not right?
Check your trigger too (optional)
Full tuning chart
Open the full tuning chart34 of 34 rows ▾▴
| Caliber | Barrel | Gas | Ammo | Suppressed | Carbine tube | A5 tube |
|---|---|---|---|---|---|---|
| 5.56 NATO | 20" | Rifle | – | No | Carbine / H1 | A5H0 / A5H1 |
| 5.56 NATO | † 20" | Rifle | – | Yes | H1 / H2 | A5H1 |
| 5.56 NATO | 18" | Rifle | – | No | Carbine / H2 | A5H0 / A5H1 |
| 5.56 NATO | 16" | Mid | – | No | H1 / H2 | A5H1 |
| 5.56 NATO | 16" | Mid | – | Yes | H2 / H3 | A5H2 |
| 5.56 NATO | ⚠ 16" | Carbine | – | No | H2 / H3, or rifle spring with a carbine buffer | A5H2 |
| 5.56 NATO | ⚠ 16" | Carbine | – | Yes | H3 or heavier, with an adjustable gas block | A5H3 / A5H4 |
| 5.56 NATO | 14.5" | Mid | – | No | H2 / H3 | A5H2 |
| 5.56 NATO | ⚠ 14.5" | Carbine | – | Yes | H3, adjustable gas block required | A5H3 / A5H4 |
| 5.56 NATO | † 13.7" | Mid | – | Either | H2 | A5H2 |
| 5.56 NATO | 12.5" | Carbine | – | No | H2 / H3 | A5H2 / A5H3 |
| 5.56 NATO | 12.5" | Mid | – | Yes | H2 | A5H2 |
| 5.56 NATO | 11.5" | Carbine | – | No | H1 / H2 | A5H2 |
| 5.56 NATO | 11.5" | Carbine | – | Yes | H2 / H3 | A5H3 |
| 5.56 NATO | 10.5" | Carbine | – | No | H2 / H3 | A5H1 / A5H2 |
| 5.56 NATO | 10.5" | Carbine | – | Yes | H3 | A5H3 |
| 5.56 NATO | † 8" and under | Pistol | – | Either | H2 / H3 | A5H1 / A5H2 |
| 300 BLK | ⚠ 16" | Carbine | Subsonic | Either | No reliable answer | – |
| 300 BLK | 10.5" | Pistol | Subsonic | Yes | H2 | – |
| 300 BLK | 8" to 9" | Pistol | Subsonic | Yes | H1 / H2 | – |
| 300 BLK | 7.5" | Pistol | Subsonic | Yes | H1 / H2 | – |
| 300 BLK | † 6.25" and under | Pistol | Subsonic | Yes | Carbine / H1 | – |
| 300 BLK | † 5.5" | Pistol | Subsonic | Yes | Carbine / H1 | – |
| 300 BLK | 7.5" | Pistol | Supersonic | No | H1 | – |
| 300 BLK | ⚠ 7.5" to 10.5" | Pistol, ported for subsonic | Supersonic | Either | H3 | – |
| 7.62x39 | 16" | Carbine | – | No | H2 / H3 | A5H1 / A5H2 |
| 7.62x39 | † 12.5" | Carbine / Mid | – | No | H2 / H3 | A5H1 |
| 7.62x39 | ⚠ 10.5" and under | Carbine | – | No | Measure your port first | See the flagged builds note |
| 7.62x39 | † 8.5" | Pistol | – | No | H2 | A5H1 |
| 6mm ARC | 18" | Rifle | – | No | H2 | A5H2 |
| 6mm ARC | 16" | Mid | – | Either | H2 / H3 | A5H2 |
| 6mm ARC | † 12.5" | Carbine | – | Either | H2 / H3 | A5H2 |
| 9mm blowback | Any | None (blowback) | – | No | 10 oz minimum deadblow, standard carbine spring. Confirm with us. | Carbine tube only |
| 9mm blowback | Any | None (blowback) | – | Yes | Heaviest that fits. Starting point, work up. Confirm with us. | Carbine tube only |
† Reasoned out, not tested. Expect to tune. Start heavy, work down.⚠ A build that fights back.The highlighted row is your current pick.
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MARC and MARC II installation
Full install, start to finish.
9mm blowback AR with the MARC
What a 9mm blowback build needs: 10 oz minimum buffer, no spacer in a carbine tube.
Two weights listed
Start with the heavier one and work down until the gun stops running, then go back up a step.Buffer type matters
A buffer stamped H2 or H3 that is one solid piece of steel carries the mass but gives no dead blow. Shake it. You should feel the weights slide.Not sure?
Email team@copperheadsafety.com with your trigger model, lower, barrel, gas length and what the gun is doing. A photo of the fire-control pocket helps.Color means tuning effort. Green: standard published setting. Amber: reasoned out, expect to tune. Orange: a build that fights back. Red: no published answer, email us. Blue: 9mm, confirm with us. This guide covers MARC and MARC II setup only and is not legal advice. Check your own state and local rules.