MARC Trigger Compatibility Chart — AR-15 FRT Fitment Guide
The MARC and MARC II are ATF-determined lawful forced reset trigger systems — one discharge per trigger pull. Both install alongside your existing fire control group, which means trigger fitment matters. This chart records our team's documented fitment experience; rows marked † are inferred from trigger geometry rather than a documented test.
Before you start: compatibility also depends on your buffer, bolt carrier group, and lower receiver. Check the buffer requirements, BCG requirements, and lower receiver requirements guides first.
The chart
| Trigger | Type | Fitment | Typical work required |
|---|---|---|---|
| Mil-spec single stage | Single stage | Drop-in | None |
| Geissele S3G / SD3G † | Single stage, short travel | Drop-in (inferred) | None expected — short, light travel keeps the trigger tail clear of the MARC axle |
| Single-stage drop-in cassette triggers † | Single stage | Generally drop-in (inferred) | None expected |
| Larue MBT-2S | Two stage | Fits with minor fitting | Trigger-tail relief, typically under 0.5 mm of material; some units also need light disconnector work |
| Geissele SSA | Two stage | Fits with minor fitting | Trigger-tail relief, typically under 0.5 mm — very light sanding and polishing is usually enough |
| Geissele SSA-E | Two stage | Fits with minor fitting | Same as SSA; auto-cam behavior is seen more often on Geissele two-stage units (see the light-strike guide) |
| Geissele G2S | Two stage | Fits with minor fitting | Same family behavior as SSA/SSA-E |
| Schmid two-stage | Two stage | Fits with minor fitting | Trigger-tail relief; in our experience Schmid units have needed more material removal than Geissele units |
† Inferred from trigger geometry, not a documented test on our bench. Open review item: confirm or delete these two rows before publish. The tuning corpus mentions S3G/SD3G only as examples of short-travel single-stage designs; the cassette-trigger row has no source at all.
Why two-stage triggers need fitting
A two-stage trigger has a longer pull than a single stage. Mechanically, the tail of the trigger has to rise higher inside the lower before the hammer drops. When the tail rises too far, it contacts the bottom of the MARC's axle before the hammer can release. The symptom: the trigger breaks in semi-auto (sometimes with a heavier pull than normal), but will not break in the active-reset position.
The documented fix is removing a small amount of material from the top of the trigger tail — typically less than 0.5 mm. We will never instruct or advise anyone to modify a sear surface.
Full step-by-step fitting procedure, including what to do if the trigger stops resetting after tail relief, is in the trigger reset troubleshooting guide.
Safety notes — read these
- Function-check on Safe frequently. Removing too much trigger-tail material can delete the surface that interfaces with the safety selector, and the weapon can become capable of firing on Safe. This is rare and only seen in extreme cases, but it has been observed. If your trigger needs material removed and a hump remains on the right (ejection-port) side of the tail, remove less material from that side — it interfaces with the safety surface.
- Trigger modification is done at your own risk. It may void the trigger manufacturer's warranty. Copperhead Safety is not responsible for damages, lack of function, loss of warranty, or unsafe firearms resulting from modifications. Individual triggers vary; the amounts described here came from our test units and yours may need more or less.
- Never modify a sear surface.
FAQ
Does the MARC II work with a stock mil-spec trigger? Yes. Standard single-stage triggers are drop-in compatible in our documented testing.
Does the MARC work with the Geissele SSA-E? Yes, with minor fitting. Most SSA-E units need light trigger-tail relief — typically under 0.5 mm, usually just sanding and polishing — so the tail clears the MARC axle in the active-reset position.
Does the MARC work with the Larue MBT-2S? Yes, with fitting. The MBT-2S nearly always requires trigger-tail relief (typically under 0.5 mm), and some units also need light disconnector work.
Why won't my two-stage trigger break in the active-reset position? The trigger tail is contacting the MARC axle before the hammer can release. Small tail relief — under 0.5 mm in most documented cases — resolves it. See the fitting guide.
Will modifying my trigger make the gun unsafe? Done correctly, no — but excessive tail removal can delete the safety-interface surface. Function-check on Safe after every pass, and stop at the minimum material removal that achieves function.
Is the MARC legal? The MARC family is ATF-determined lawful — one discharge per trigger pull. State restrictions apply; see our shipping restrictions page.