MARC II (Ambi) - Milspec Active Reset Conversion
The Milspec Active Reset Conversion is a three-position active reset device system. The MARC II is the ambidextrous build: an extended control surface on both sides of the receiver instead of one. We hold it to the same tolerances and materials we run in our own rifles: clone-correct geometry, an S7 tool steel lever, a 4140 selector lever. Every configuration listed here ran in a test gun before we put it up for sale.
Watch Before You Install
Full written install guide: copperheadsafety.com/learn/marc-installation
The Milspec Active Reset Conversion is a three-position active reset device system. The MARC II is the ambidextrous build: an extended control surface on both sides of the receiver instead of one. We hold it to the same tolerances and materials we run in our own rifles: clone-correct geometry, an S7 tool steel lever, a 4140 selector lever. Every configuration listed here ran in a test gun before we put it up for sale.
What the MARC II Adds
- Levers on Both Sides — the selector carries a control surface on the left and the right, so every position stays reachable without breaking your firing grip.
- Built for Left-Handed Shooters — southpaws get the same access to all three positions that right-handed shooters have always had.
- Extra Surface Area for Right-Handed Shooters — the second lever gives your trigger finger or support thumb another contact point for fast mode changes.
- Everything Else Is the Standard MARC — same S7 tool steel lever, same 4140 selector, same nitride coating, same three-position operation, same installation requirements.
Only need one side? The standard MARC is the same system with a single left-side lever, $25 less.
Product Features
- S7 Tool Steel Lever — heat treated and nitride coated, so the contact faces hold their shape through long strings of fire
- 4140 Steel Selector Lever — the mil-spec material, with no cheaper stand-in anywhere in the part
- Engineered Interaction Surfaces — we hold tight tolerances on the mating faces so the lever never binds against the trigger during hammer reset
- Rounded Edges — we radius every lever edge, since sharp corners concentrate stress and start cracks
- Three-Position Operation — standard semi, enhanced semi, and full reset modes
- Ambidextrous Configuration Available — more control surface for left and right-handed shooters; the extra lever face makes mode changes easier even if you shoot right-handed
- Clone-Correct Profile — cut to mil-spec geometry, so it drops into a standard lower receiver
- S7 Tool Steel
- Simple Drop-In Installation
- No Super Safety Cut Required
- 3-Position
- AR-15 Platform
- Standard & Ambi
- Broad Trigger Compatibility
- Clone Correct Aesthetic
FRD Requirements Checklist
- Sufficient Buffer Weight — your rifle needs a heavy enough buffer to stop bolt bounce. Bolt bounce gives you a dead trigger and light primer strikes. If you get either one, add buffer weight before you change anything else. Start with the tuning table below.
- M16-Cut Bolt Carrier Group (BCG) — the lever needs the full-profile carrier to reset the hammer. A semi-auto cut BCG will not run.
- Low-Shelf Lower Receiver — you need a low-shelf lower, or you need to be comfortable cutting your existing lower to low-shelf.
- Geissele Over Travel Stop — only if you run a Geissele trigger. We sell them separately.
Standard Test Configurations
Aero Precision Gen 2 Lower / M4E1 Lower
Standard carbine buffer tube · carbine spring · H2 buffer
A5 buffer tube · A5 spring · H1 buffer
Find your caliber in the chart, then match on gas system length before barrel length. Gas length moves the answer further than barrel length does, and rifle gas often runs with no buffer change at all.
A low back pressure can moves the answer down a step. A conventional one holds it up.
Subsonic 300 BLK needs the can on to cycle. That is normal for those builds, not a fault.
Running the A5 column? It takes a rifle-length spring, not a carbine one, and the tube’s extra length costs you spring force. Start with a mil-spec rifle spring. An extra-power rifle spring in an A5 is a common cause of a gun that will not lock back. On short 300 BLK the A5 runs out of adjustment, because its lightest setting still weighs more than a stripped carbine buffer, which is why the 300 BLK chart has no A5 column.
Tuning Recommendations
These numbers come off our own test guns. Consolidated community reports fill in the rest. Your build may want something different.
Tuning chart, by caliber 32
5.56 NATO
| Barrel Length | Gas System Length | Suppressed | Carbine Tube | A5 Tube |
|---|---|---|---|---|
| 20" | Rifle | No | Carbine / H1 | A5H0 / A5H1 |
| † 20" | Rifle | Yes | H1 / H2 | A5H1 |
| 18" | Rifle | No | Carbine / H2 | A5H0 / A5H1 |
| 16" | Mid | No | H1 / H2 | A5H1 |
| 16" | Mid | Yes | H2 / H3 | A5H2 |
| ⚠ 16" | Carbine | No | H2 / H3 or Rifle Spring + Carbine Buffer | A5H2 |
| ⚠ 16" | Carbine | Yes | H3 or heavier, with an adjustable gas block | A5H3 / A5H4 |
| 14.5" | Mid | No | H2 / H3 | A5H2 |
| ⚠ 14.5" | Carbine | Yes | H3, adjustable gas block required | A5H3 / A5H4 |
| † 13.7" | Mid | Either | H2 | A5H2 |
| 12.5" | Carbine | No | H2 / H3 | A5H2 / A5H3 |
| 12.5" | Mid | Yes | H2 | A5H2 |
| 11.5" | Carbine | No | H1 / H2 | A5H2 |
| 11.5" | Carbine | Yes | H2 / H3 | A5H3 |
| 10.5" | Carbine | No | H2 / H3 | A5H1 / A5H2 |
| 10.5" | Carbine | Yes | H3 | A5H3 |
| † 8" and under | Pistol | Either | H2 / H3 | A5H1 / A5H2 |
300 BLK
| Barrel Length | Ammo | Gas System Length | Suppressed | Carbine Tube |
|---|---|---|---|---|
| ⚠ 16" | Subsonic | Carbine | Either | No reliable answer |
| 10.5" | Subsonic | Pistol | Yes | H2 |
| 8" to 9" | Subsonic | Pistol | Yes | H1 / H2 |
| 7.5" | Subsonic | Pistol | Yes | H1 / H2 |
| † 6.25" and under | Subsonic | Pistol | Yes | Carbine / H1 |
| † 5.5" | Subsonic | Pistol | Yes | Carbine / H1 |
| 7.5" | Supersonic | Pistol | No | H1 |
| ⚠ 7.5" to 10.5" | Supersonic | Pistol, ported for subsonic | Either | H3 |
7.62x39
| Barrel Length | Gas System Length | Suppressed | Carbine Tube | A5 Tube |
|---|---|---|---|---|
| 16" | Carbine | No | H2 / H3 | A5H1 / A5H2 |
| † 12.5" | Carbine / Mid | No | H2 / H3 | A5H1 |
| ⚠ 10.5" and under | Carbine | No | Measure your port first | See the flagged builds note |
| † 8.5" | Pistol | No | H2 | A5H1 |
6mm ARC
| Barrel Length | Gas System Length | Suppressed | Carbine Tube | A5 Tube |
|---|---|---|---|---|
| 18" | Rifle | No | H2 | A5H2 |
| 16" | Mid | Either | H2 / H3 | A5H2 |
| † 12.5" | Carbine | Either | H2 / H3 | A5H2 |
Buffer key, lightest to heaviest: Carbine · H1 · H2 · H3 · A5H4
† marks a starting point we have reasoned out rather than tested. Expect to tune those. Start heavy and work down.
5.56, 16", carbine gas — long dwell and high port pressure, so a violent unlock and a fast carrier. The hardest common build to get a clean reset from. An adjustable gas block buys you the most.
5.56, 16", carbine gas, suppressed — everything above with back pressure stacked on top. Pick a different gas length if you have not bought the barrel yet.
5.56, 14.5", carbine gas, suppressed — more gas into the carrier than a fixed port can manage. Do not build this one without an adjustable gas block.
300 BLK, 16", carbine gas — usually will not cycle subsonic at any buffer weight, with or without a can. Pistol gas is the right choice at this length.
300 BLK ported for subsonic, running supersonic — over-gassed, and no single port size serves both. An adjustable gas block or adjustable carrier is a requirement here, not an upgrade.
7.62x39, 10.5" and under — factory ports run anywhere from .070" to .125". One will not cycle at all, the other is badly over-gassed. Measure your port before you buy anything. On this cartridge the bolt is the wear item, not the buffer.
Direct Blowback AR-9/PCC
9mm Blowback ARs — a blowback PCC cycles and recoils far more violently than a gas-operated AR. The bolt slams rearward under nothing but raw case pressure and spring, and everything downstream of it takes that impact directly. Run at least a 10 oz buffer, or the heaviest captured or hydraulic buffer that fits your tube.
Running any Copperhead FRD product, including the MARC, in an AR-9 with an unmodified bolt weight voids your warranty as gross negligence. Tune the gun first.
Blowback9 on YouTube covers PCC tuning in more depth than we can fit here.
Before you order for an AR-9
The bolt in a 9mm AR carries a separate rear weight, and on most carriers that weight sits in the space the lever needs to swing through. Notch it so the lever clears. Do not remove it altogether, because that weight is part of the mass the gun needs. Builders who skip this step report the bolt locking up, and levers bending and breaking.
Buffer length is a separate constraint from buffer weight, and it traps people both ways. A 9mm bolt needs about 3 inches of travel for the lever to reset. A carbine tube is 7 inches and a 9mm buffer is 4, which leaves exactly that. Stack a spacer into a carbine tube and you short-stroke the gun. Run a bare 9mm buffer in a longer A5 tube and you get roughly three quarters of an inch of overtravel that will eventually break the bolt catch. Use the A5 only if you are filling that space with spacer weight. Check yours by pulling the bolt fully to the rear by hand: the bolt face should stop about an eighth to a quarter inch behind the bolt catch.
Do not fit a 5.56 H2 or H3 in a 9mm gun. They are too short and far too light for a blowback action.
Roller-delayed and radial-delayed uppers behave differently, and the buffer mass guidance above does not carry across to them.
Recommendation
| Buffer weight | 10 oz minimum |
| Buffer length | About 4 in |
| Buffer tube | Carbine |
| Spring | Standard carbine |
| Bolt weight | Notched, not removed |
| Suppressed | Heaviest that fits |
Use an A5 tube only if you are filling the extra length with spacer weight. Nobody publishes a tested buffer weight for a suppressed blowback PCC, so treat the suppressed row as a starting point and work up.
Buffer type matters as much as buffer weight. A buffer stamped H2 or H3 that is one solid piece of steel carries the mass but delivers no dead blow, and it will not stop bolt bounce. Shake the buffer before you install it. You should feel the weights slide inside.
Trigger Compatibility
This list is not exhaustive, and it is not a guarantee. A trigger we left off may run fine, and one marked YES can still fight you in an odd build, since your lower, your buffer, and the trigger's own tolerance stack all move the result.
Trigger compatibility chart 32
| Brand | Model | Type | Compatible |
|---|---|---|---|
| Geissele | SSA | Two Stage | YES * |
| Geissele | SSA-E | Two Stage | YES * |
| Geissele | S3G | Single Stage | YES |
| Geissele | SD3G | Single Stage | YES |
| Geissele | G2S | Two Stage | YES * |
| Geissele | SD-E | Two Stage | YES * |
| Geissele | SSAEX | Two Stage | MODIFICATION REQUIRED |
| Geissele | SSAX | Two Stage | MODIFICATION REQUIRED |
| LaRue | MBT-2S (Flat & Curved) | Two Stage | MODIFICATION REQUIRED |
| CMMG | Milspec | Single Stage | NO |
| DPMS | Milspec | Single Stage | NO |
| Jacob Gray | Single Stage | Single Stage | YES |
| MimTac | MimTac Drastic | Single Stage | YES |
| Noveske | Single Stage | Single Stage | YES |
| PSA | EPT | Single Stage | YES |
| PSA | Custom SS Drop-In | Single Stage | YES |
| Rise Armament | Rave 140 | Single Stage | YES |
| Rise Armament | RA-434 | Single Stage | YES |
| Rise Armament | RA-535 | Single Stage | YES |
| Rise Armament | RA Blitz | Single Stage | YES |
| Rise Armament | RA LE145 | Single Stage | YES |
| Rise Armament | ICONIC | Two Stage | NO |
| Schmid Inside | Two-Stage | Two Stage | MODIFICATION REQUIRED |
| Schmid Inside | Pro Line | Single Stage | YES |
| Schmid Inside | GI Flat Face SS | Single Stage | YES |
| Schmid Inside | Match Flat Face SS | Single Stage | YES |
| Smith Defense | AR-15 LPK | Single Stage | YES |
| Sons of Liberty Gun Works | SOLGW LFT | Single Stage | YES |
| Spikes Tactical | ST Battle | Single Stage | YES |
| Timney | Competition 3LB | Single Stage | YES |
| Timney | Calvin Elite | Single Stage | YES |
| Heckler & Koch | HK MR556A1 | Single Stage | NO |
* Geissele two-stage triggers marked YES sometimes want a little polishing, or a small amount of material taken off the top of the trigger shoe tail, because the longer travel stacks up against the lever. The install guide walks through it.
Firearm Functionality
This product, when properly installed and left unmodified, is designed and intended solely for lawful semi-automatic operation. It is not capable of automatic fire, nor is it readily convertible to enable automatic or burst-fire operation. The MARC actively resets the trigger, producing one discharge per individual trigger pull, in full compliance with applicable federal firearm law. End users are responsible for understanding and complying with all state and local regulations applicable to their jurisdiction.
Intellectual Property
The MARC operates on general mechanical principles consistent with those recognized as lawful in prior judicial and regulatory determinations. It does not use, reproduce, or infringe upon any patented, copyrighted, or otherwise protected intellectual property belonging to any third party.
The trigger group interaction and reset system were developed entirely in-house, without access to or use of any competitor's CAD files, proprietary data, or patent-protected materials. The MARC incorporates distinct mechanical geometry, material composition, and sequencing that result in substantial design deviations, reflecting independent engineering judgment and upgraded material selection.
The mechanical act of resetting a trigger or releasing a hammer at defined points in an operational cycle represents a functional process within the public domain and is not subject to copyright protection. The MARC features aesthetically distinct components — including a modified mil-spec safety selector profile and externally visible differences — providing clear differentiation in both form and trade dress.
Inquiries
Copperhead Safety LLC is committed to transparency and good-faith communication. Any individual or entity with questions or concerns regarding the design, function, or legality of our products is encouraged to contact us prior to pursuing legal action.
Contact: admin@copperheadsafety.com
