Anyone can buy a forced reset selector. Getting it to run as one system with the rest of the gun is the hard part. That’s why we built the One Horse Express around the Atrius FRS, and fit, tune and test every one at the factory.
The One Horse Express Series pairs Atrius Development Group’s Forced Reset Selector with a complete, factory-built firearm engineered to run as one system. If you’re researching a forced reset setup, the Express takes the biggest challenge off your plate: making every component work together.
Anyone can buy a selector, fire control group, gas system, bolt carrier, buffer and spring. Getting those parts to work together, with the correct receiver geometry, trigger profile, gas delivery, timing and bolt carrier movement, is where the real work begins. That work takes time. When the first combination is wrong, it costs money too.
We did not treat the Atrius FRS as another accessory to install in an existing firearm. We built the One Horse Express around it.
The Atrius Forced Reset Selector, or FRS, from Atrius Development Group, replaces the traditional safety selector in a compatible AR-pattern firearm. It does not replace the entire trigger or fire control group. It gives you three clearly defined positions:
The safety is on. Keep the selector on SAFE any time you are not ready to shoot.
Standard semi-automatic. After each shot you let the trigger out to reset it yourself, like a regular AR-15.
The forced reset position. As the bolt carrier moves through its cycle, the selector returns the trigger to its ready position after each shot.
You keep the same familiar AR-pattern controls in all three positions. The selector is the heart of the system, but it can’t do the job alone. Read the full Atrius FRS guide ›
Atrius designed the FRS as a drop-in solution for compatible AR-pattern firearms. Compatibility still matters.
There’s also tolerance stacking. Small dimensional differences between receivers, triggers, selectors, carriers and other parts can add up and affect fit, timing and function.
Then there’s the operating system itself. Barrel length changes timing. Gas-system length changes timing. Gas-port size, ammunition, carrier mass and the buffer and spring setup all influence how hard the action cycles.
The Atrius FRS depends on that cycle to reset correctly. If the firearm is under-gassed, over-gassed, cycling too hard or built from parts that don’t interface properly, you can be left diagnosing problems instead of enjoying the firearm.
“Drop-in” describes how the selector is installed. It does not mean every combination of parts is already balanced as a complete system. The One Horse Express is.
Same Atrius forced reset selector. A very different amount of work on your end.
| Step | DIY selector install | One Horse Express |
|---|---|---|
| The parts | You source the selector, fire control group, bolt carrier, buffer and spring, then confirm your receiver fits. | The Atrius FRS and compatible core components, selected to function as one complete operating system. |
| The research | Hours of compatibility research before the first part is ordered. | Already done before it leaves our facility. |
| Fit and timing | Tolerance stacking, gas timing and the buffer and spring setup are on you. | Fitted, timed and tuned for each Express platform. |
| Testing | Your own installation, function checks and live-fire testing. | Function-tested and live-fire validated by One Horse. |
| If it doesn’t run right | Troubleshoot one part at a time: more buffers and springs, more ammo, maybe gunsmith fees, shipping costs and weeks without the firearm. | The tuning work is already done. Tested. Tuned. Built To Run™. |
| Day one | A tuning project. | Pick it up from your FFL dealer. Load it. Run it. |
Every One Horse Express is assembled as a complete firearm around the Atrius FRS, not retrofitted after the fact. Before an Express leaves our facility, the components that affect FRS function have already been selected, fitted and tuned to work together:
This isn’t one generic parts recipe repeated across every firearm. Each Express platform gets the configuration its operating system requires. That’s the difference between installing a part and engineering a firearm around it.
Different platforms, same factory-tuned standard. Limited-finish Express rifles add personality without changing the proven foundation underneath.
The original Express, built from the ground up around the Atrius FRS. It uses a 4150 CrMoV Enhanced SOCOM Profile barrel with a 1:8 twist and a mid-length gas system. The barrel is thicker near the chamber, which adds rigidity and thermal mass and keeps the balance closer to you. That improves control and helps manage muzzle rise.
The same factory-tuned approach in a more compact 5.56 platform. Both use a carbine-length gas system with a tuned buffer and spring system matched to the shorter operating cycle. Each is assembled, fitted, timed and tested as a complete FRS-equipped firearm.
The platforms are shorter. The standard stays the same.
Dedicated rimfire operating systems, not a basic conversion running through a centerfire barrel. A rimfire-specific interface lets the dedicated bolt work with the three-position Atrius FRS.
Different cartridge. Different operating system. Same factory-tuned standard.
Building your own FRS-equipped AR-15 can take hours of research before the first part is ordered:
Then come installation, function checks and live-fire testing. If it doesn’t run right, the troubleshooting starts, one part and one variable at a time.
With the One Horse Express, that work is done at the factory. No compatibility chart, no chasing a timing issue, no range trips spent swapping parts. Pick it up from your FFL dealer, load it and run it.
The potential savings go far beyond the price of one component.
None of it buys you meaningful range time.
The One Horse Express provides the Atrius FRS, compatible core components, factory installation, platform-specific tuning and live-fire validation as one complete package.
You are not paying us to put a selector in a firearm. You are investing in a firearm engineered around the selector.
Every Express comes with the Atrius forced reset selector installed, tuned and tested at the factory.
Every Express rifle and pistol carries a limited lifetime warranty. Firearms ship only to a licensed FFL dealer. Free shipping on all Express rifles and pistols, and on any other order over $399. You must be at least 18, or 21 where state or local law requires it (21 for handguns, including AR-style pistols). Check your local laws before you buy.
Atrius Development Group developed a rugged three-position Forced Reset Selector built around familiar controls. One Horse took that technology and engineered complete American-made firearms around it.
That partnership is more than two names on a receiver. It brings selector design, firearm manufacturing, system-level tuning and final testing together before the product reaches you.
Atrius builds the FRS.One Horse builds the platform.Together, we remove the guesswork.
No. The part installed in the One Horse Express is the Atrius Forced Reset Selector, or FRS. It is a forced reset safety selector, and it replaces the firearm’s selector, not the entire fire control group.
In the Super-Semi position, the FRS works with the cycling bolt carrier to return the trigger to its ready position after each shot. That is the forced reset. The selector, fire control group, gas system, bolt carrier group and tuned buffer and spring system must work together for consistent function.
The One Horse Express is tuned, tested and Built To Run™ in its factory configuration. The Atrius FRS and the parts that affect how it works are fitted and tested before the firearm leaves One Horse. Major changes to the gas system, bolt carrier group, fire control group, buffer and spring system or suppressor setup may affect cycling and should be checked separately.
A factory-tuned FRS rifle removes the compatibility research and the trial and error that come with building a forced reset system from separate parts. It can save you time, ammunition, replacement parts and possible gunsmith fees.
The Atrius FRS installed in the One Horse Express has three positions: SAFE, SEMI and Super-Semi. See how each position works.
The One Horse Express Series: 16-inch 5.56 rifles, 10.5-inch 5.56 pistols (MLOK and Quad Rail), a dedicated 16.1-inch .22 LR rifle and a dedicated 12.1-inch .22 LR pistol. See the full Express lineup.
Pick your Express on theonehorse.com and check out online. We ship it to the licensed FFL dealer you choose at checkout. At the dealer you fill out ATF Form 4473 and pass a background check before you take it home. Free shipping on all Express rifles and pistols, and on any other order over $399. You must be at least 18, or 21 where state or local law requires it. Federal law sets 21 as the minimum age to buy a handgun, including an AR-style pistol, from a licensed dealer. Read our step-by-step guide to buying a gun online.
Laws vary by state and city and can change. It is the buyer’s responsibility to know and follow federal, state and local laws where they live and where they shoot, including rules on triggers and selectors. Placing an order does not mean an item is legal where you live. This article is product information, not legal advice.
Stock One Horse Express rifles and pistols with the Atrius FRS installed, tuned and tested, at dealer pricing. Apply online: upload your FFL and tax-exempt document, and our team will reach out about our programs and pricing.
No compatibility scavenger hunt. No pile of unused springs and buffers. No range time burned trying to find the right combination. Just a complete, factory-built firearm with the Atrius FRS installed, fitted, tuned, tested and ready.
American Made · Family Owned · Veteran Owned
Not legal advice. This article describes the Atrius Forced Reset Selector and One Horse Express firearms. Federal, state and local laws vary and change, and it is the buyer’s responsibility to follow them. Placing an order does not mean an item is legal where you live. Questions? Call 812-200-0305 or email [email protected].
