REVIEW: One Horse 300 BLK SD AR Pistol

Galloping seemingly out of nowhere, One Horse has reignited the AR segment in less than a year with its all-American-made manufacturing and no-nonsense commitment to quality…at affordable prices. Now we give One Horse a ride, testing the company’s 300 BLK SD AR Pistol.

by Rob Reaser

Purveyors in the AR-15 segment have become accustomed to the boom/normal cycling of the marketplace. Heritage manufacturers take advantage of the booms often by scaling margins upward, leveraging their brand name to gain a few more cents on the dollar. Nothing wrong with that at all. That’s capitalism. When the normal returns, there is justification for holding pat until the next surge. The resources are usually in place to do it.

Boom cycles also bring out the “me, toos” — and the AR segment is especially vulnerable to these startups. When everyone is buying ARs, assembling and selling them is not a heavy lift. That’s assuming the components can be sourced. But when the excitement wanes for whatever reason, we find their houses are built on sand, not stone. The post-Obama era put that into clear focus. The same with the Covid years. Everybody and their cousins were making ARs for a short while.

Today, their warranty cards are worthless, their phone lines disconnected.

So, how is it that one particular company has had the grit to not only start up an AR manufacturing concern from scratch, but also to be explosively successful in the doing at a time when the AR segment is supposedly in a deep, now years-long slump? A time when critics will posit that AR ownership has thoroughly saturated this country and the salad days are now well behind us?

Let’s call it determination and faith. Determination in the same spirit that founded this country 250 years ago — never give up and never quit despite the odds and the naysayers. Faith in the resolve of solid American craftsmen, tradesmen, and their belief that hard work for honest pay still means something and that like-minded consumers will reward noble efforts — a communion of the brotherhood, so to speak.

Review: One Horse 300 Blk Sd Ar Pistol — The One Horse principals leading from the front line: Drew Markel (left) and Jeremy Hammons (right).

I don’t mean to wax poetic here, but a brief conversation I had in January of this year, standing in the middle of the Venetian casino while hundreds of people streamed past us like water flowing around a rock, has been made manifest. I admit that I had doubts — the same doubts others had expressed — when Jeremy Hammons and Drew Markel explained they had launched a new company called One Horse only two months prior.

A Bit of Background

AR-15 fans — especially those in the DIY crowd — are quite familiar with a former company out of Hebron, Kentucky, called Anderson Manufacturing. For years, Anderson was the primary parts source for AR folks looking to build their own rifles, carbines, SBRs, and pistols. What most folks don’t know is that Anderson was also the key manufacturer/supplier of OE parts across the AR-15 landscape. In other words, many big-name manufacturers tapped Anderson as their source for components to build their own rifles.

Jeremy Hammons, a U.S. Army veteran and founder of One Horse, earned his industry chops while working at Anderson — starting when the company first began to transition from a general machine shop to the high-volume AR component manufacturer for which they had become best known. By the time the Anderson owners decided to close shop and sell to Ruger in 2025, Jeremy sat as the VP of sales and marketing and enjoyed deep connections across the firearms industry.

Opening a Chasm: The Ruger Acquisition

The AR world took a bit of a rocking on July 1, 2025, when Sturm, Ruger & Company announced the asset purchase of Anderson Manufacturing. This reveal came on fast, hard, and definitively. In one stroke, Anderson — a company that AR manufacturers and home-grown consumers had depended on as a key source for AR build components and accessories was no more.

Lights out.

Website shuttered.

Coming out of the Covid era and the years-long lag of the resulting supply chain disruptions, this was a huge gut punch for the AR segment at a time when it was already tangled in the ropes of a downturned economy and suppressed consumer demand.

But where others saw despair, Jeremy and Drew saw an opportunity. The wrap-up of Anderson Manufacturing left a massive crater on the AR landscape. Consumers still wanted to build their own guns, new shooters still wanted their first AR-15s (at affordable prices), and small-scale AR manufacturers still needed quality components to keep the lights on and to pay their employees.

One Horse Unbridled

While OE manufacturing and supplying get most of the credit for Anderson’s success, the company earned a deserved reputation for catering to the Everyman AR guy and gal, providing a source of parts at affordable prices so folks could build, modify, or repair their own firearms. In other words, there was a focus on and an earned following of mainstream, work-a-day AR enthusiasts.

With the One Horse inception, Jeremy and Drew effectively built on that fundamental premise and amped it up to an even higher red, white, and blue level.

In sum…America first and 2A all the way.

Great ideals, but how does that translate past clichéd, overused slogans?

Let’s start with the America first theme.

For the Home Team

Unbeknownst to most consumers, many of the components that make up an AR-platform firearm are manufactured outside of the country and done so on the cheap. For most of us (this writer included), having “America’s rifle” sporting parts made overseas is nothing short of blasphemy.

But beyond the patriotic significance of that, there are the expected economic consequences. A part made outside of the U.S. means a potential worker in this country didn’t earn a paycheck for making said part. That impact grows exponentially when you consider all other workers in that hypothetical supply chain.

One Horse is committed to using only components manufactured in the U.S. by American workers. The goal, as stated by Jeremy and Drew, is to ensure that every One Horse product purchase — be it a single component, a build kit, or a complete firearm — supports not only One Horse employees but also American businesses and employees all the way back to the beginning of the supply chain.

Naturally, that would lead most folks to the presupposition that One Horse products (like many made-in-America only products) would come at a premium price tag.

Not so…and a quick look at One Horse firearm prices proves the point. As of this writing, the company offers nine different rifle models under $700 — the lowest-priced rifle being $549.99. Again, that is a 100-percent American-made firearm.

That entry-level price point for a solid, basic, out-of-the-box AR represents another leg of the One Horse philosophy, and that is that the AR platform should not be intimidating to newcomers.

Those of us who have been shooting ARs for a considerable time may not be aware that the whole tactical mystique, which has developed around the ARs over the last couple decades, can give newbies pause. Jeremy stated that they want their guns to be approachable not only in price but in simplicity and reliability — a configuration the first-time buyer can easily understand and feel comfortable handling from the outset. This further opens the door to bring average Americans into the shooting space and to give them an on-ramp to “America’s rifle.”

The other guiding light for the One Horse team is to be totally unafraid and unapologetic in the exercise of our Second Amendment right.

Sure, you would expect a gun company to say that. So, how does One Horse go about walking the walk?

There’s no better illustration than the recently introduced One Horse Express rifles and pistols chambered in 5.56 NATO and 22 LR.

“Whoop-dee-doo,” you say?

Here…hold my reins.

Bold and Brash

Some of you may have heard of an innovation in rapid-fire semi-auto AR technology by a company out of Texas called Atrius Development Group. Not having any experience with this technology (yet), I’ll refrain from saying anything about it other than the facts published by Atrius. Check out the Atrius website for details or watch the brief One Horse video below for an eye-opener.

The short version is that Atrius developed what the company calls a “forced reset selector” or FRS.

Most of you in the AR superfan space know about forced reset triggers (FRT). These triggers, when properly adjusted and tuned, sometimes provide a quick trigger reset that permits faster follow-up shots than does a conventional semi-auto trigger. But the operative phrase here is “properly adjusted and tuned.”

I’ve messed with FRTs a little bit. Some may like them. Mine went into the trash after testing. Literally…into the trash can.

The Atrius FRS, though, is not a forced reset trigger; it is a forced reset selector — one that replaces the MILSPEC safety selector and works with MILSPEC (and some cartridge) triggers in lower receivers featuring a low shelf or full-profile trigger pocket.

The Atrius forced reset selector has three positions: no bang, semi-auto bang, and semi-auto hold-on-tight-bang. [Ready to watch that video now?]

Here’s where One Horse puts its 2A street cred on the table.

The entire One Horse Express lineup comes from the factory with an Atrius FRS installed in place of the conventional safety selector. No other manufacturer offers an Atrius FRS system in a regular production firearm, and none (to my knowledge) have ever offered any type of forced reset trigger in their products.

This is something new in the industry…a first…and it took a pair of big ones for a gun maker to do it.

What does this have to do with One Horse’s 2A support?

It shows the company stands by the principle that fully exercising our 2A right is key to keeping that right fully intact. Where some manufacturers may be weak-kneed about taking such a bold stand, the One Horse crew seems to say, “Well then, get out of our way!”

That’s refreshing.

The One Horse 300 BLK SD AR Pistol

For my first rodeo with One Horse, I chose to try out the company’s take on a 300 BLK pistol. This one comes with the standard MILSPEC trigger and safety selector, not the Atrius forced reset selector, and sports a 10.5-inch barrel.

As a factory AR pistol goes, the model offers nothing unexpected. Operational controls are familiar, as is the A2 grip and flat trigger guard. Although I’m not a big fan of having my firearm be a billboard for manufacturer marketing, I actually dig the One Horse logo treatment. It comes off as a modest nod to its origins and simply looks cool.

As with many factory AR pistols, One Horse tapped SB Tactical’s SBA3 stabilizing pistol brace to bring up the tail end of this feisty firearm. It offers five-position length adjustment and features an ambidextrous QD pocket for sling attachment.

Rather than a low-buck phosphate treatment, the bolt carrier group is finished in black nitride, which delivers slick operation and the promise of easy cleaning. A forward assist is in keeping with the original AR heritage, as is a MILSPEC charging handle. A flattop receiver gives you sighting options. I chose to drop a Bushnell RXS-250 onto the integrated Picatinny rail atop the One Horse 15-inch handguard.

“Wait a minute,” you say. “A 15-inch handguard over a 10.5-inch barrel?”

Yes. And that leads us to the “special feature” of my test model.

The One Horse OH-OP04 includes the company’s RYN .30-caliber suppressor as standard factory equipment. That means (at least for now) you’ll need to go through the Form 4 process to acquire the gun. But what you get is a .30-cal. can that’s tucked neatly inside the handguard — hence the “SD” designation.

I’m sort of on the fence about the SD concept (see the H&K MP5SD to answer your “What the heck is SD?” question). On one hand, I appreciate the extra acreage this configuration offers for support-hand grip positioning, accessory placement, and protection from scorching metal.

On the other hand, I prefer full access to my suppressor adapter and muzzle device to allow detailed cleaning and service. As you can see here with the RYN suppressor removed, that kind of access ain’t happenin’ without first removing the handguard.

But that’s a minor issue in this case because the OH-OP04 comes with a Plan B mount (interfaces the suppressor with the muzzle device) and a Plan B flash hider. This solves a couple of issues for the consumer. One, you don’t need to buy an adapter to mount the RYN suppressor. The gun comes with everything you need. Two, the Plan B system uses a tapered profile and fine threads to mitigate most of the carbon fouling and mess associated with non-tapered or mechanical lock mounting systems.

That is not to say you’ll have a super-clean experience running ammo through this setup. For my testing, I used Fiocchi’s Hyperformance Defense SBR Enhanced 125-gr. for the supersonic loading and SBR Enhanced 220-gr. for the subsonic loading. Particulate blowback wasn’t much to talk about; however, gas from the supersonic loads was downright obnoxious during fast-fire drills. My eyes were burning.

Blowback aside, the gun ran flawlessly, with no hiccups during the cycle of operation with either subsonic or supersonic ammo. The One Horse crew put together a well-tuned system.

After zeroing the red dot, I ran mostly Mozambique Drills (two shots to the chest, one to the head) at 10-15 yards. Throughout, the OH-OP04 proved nimble, responsive, and as accurate as I could shoot it at speed. As far as reliability and defensive performance, you need not ask for anything more. And given the package price — which includes the RYN suppressor and Plan B mounting system — of $1,299.99, there’s nothing to complain about.

If you want a similar gun without the RYN suppressor and the Form 4 hassle, you should check out the OH-OP02 model at only $699.99. The primary difference is that this gun uses the Mission First Tactical BATTLELINK Minimalist brace instead of the SBA3.