Trigger Compatibility for Atrius FRS X-Series

What Triggers are Compatible with the Atrius FRS X-Series?

So you just bought your new FRS X-Series and you want to know what triggers are compatible with this Forced Reset Selector. Understandable! We've compiled our anecdotal experiences, product knowledge, and some images to help you make the best decision.

Users can also check out our Atrius Community Compatibility Sheet which includes compatible parts, accessories, and platforms provided by members of our own team and hundreds of customers that have shared their feedback with us.

Note for MPX Owners

The Sig Sauer MPX platform is offered in three configurations: MPX-K, MPX PCC, and MPX Copperhead. These platforms can come in one of two triggers. Ensure you have the correct trigger to be compatible with the X-Series Forced Reset Safety.

MPX-Compatible Triggers for the X-Series

Triggers MPX Platforms can come with:
1. Schmid Mil-Spec Single Stage 3.5 lb Curved Trigger (COMPATIBLE)
2. Timney Single Stage 3.5 lb Flat Drop-In Trigger for MPX (NOT COMPATIBLE)

Drop-In Timney AR PRO Trigger is Not Compatible w/ FRS X-Series

Historically, a variety of Timney triggers work great with the Standard Single, Ambi, and Mil-Spec FRS versions when used in an AR15 - but unfortunately that compatibility is not shared with the MPX.

Drop-In Timney Impact AR Trigger is Not Compatible w/ FRS X-Series

Note for MCX Owners

The Sig Sauer MCX platforms come in several variants from the factory. For compatibility with the FRS X-Series, ensure you are using a Spear-LT model which is essentially utilizing AR-15 calibers. (The MCX Spear, often referred to as the “Heavy” is chambered in .308 WIN and .277 Fury. FRS Compatibility for the Spear Heavy is why we created the X-Series Heavy.

The MCX Spear LT will typically come with one of these two triggers:

1. Schmid Mil-Spec Single Stage 3.5 lb Curved Trigger (COMPATIBLE)
2. 2. Sig Sauer Two Stage AR Match Duo (NOT COMPATIBLE)

MCX-Compatible Trigger for the X-Series

This image does not include the hammer portion of the trigger group, just the trigger bar, disconnect, and trigger spring.

Regardless of whether the trigger that came with your MCX is silver or black in color, if it looks like the image above, it will be compatible with the X-Series FRS. You can see here circled in green what users should look for when seeking compatible triggers to be paired with their Forced Reset Selector.

In general, all you need is for a mil-spec trigger to be single stage, and without a U-notch, relief cut, or ramp, with as flat of a trigger bar as possible. Users are free to polish their trigger bars as well for increased compatibility as there is not a true standard for “mil-spec” trigger groups with manufacturers varying in dimensions, design, and style.

Why the Sig AR Match Duo Two Stage is not compatible with the X-Series

Not that there’s anything wrong with the skeletonized trigger design, that’s just the easiest way to identify this trigger so we circled that. The dimensions that do interfere with the FRS functioning properly are also circled in red. Notice that this trigger, while it is a 2-piece mil-spec inspired design, features an open trigger bar with multiple ramps and relief cuts. Our Forced Reset Solution requires that the trigger bar be enclosed.

Final Verdict & Atrius Recommendations

For simplicity, it's best to run with a single stage mil-spec trigger in the MCX Spear-LT, MPX-K and MPX PCC when pairing it with the Atrius X-Series FRS. If users discover new trigger compatibility please let us know and we will update the Community Compatibility Tracker. Dirty Bird Nickel Teflon Single Stage Trigger Group They offer it in a cursed and a flat face trigger option. It’s the best bang for your buck in terms of performance, reliability and cost.