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6mm ARC Redo

San Tan Tactical STT 15 6ARC on table

As an avid shooter and rifle enthusiast, I have always been on the lookout for the latest and greatest in firearms technology. Recently, I had settled on the 6mm ARC cartridge and considered myself well-equipped. However, after sharing my thoughts on the cartridge in a recent write-up, I received a flood of inquiries from friends and fellow shooters who were also considering the 6mm ARC or had already adopted it.

This got me thinking:

what are the best options for a semi-auto, direct-impingement (DI) rifle in 6mm ARC?

And how does the recoil impulse of the 6mm ARC compare in a DI gun?

I did not have all the answers, but these among others were compelling questions.

Research and Findings

Some of the new 6mm ARC adoptees in my circle had gone with the UPR15, which I highly recommended. Some had simply gone this-this-or-that companies’ upper. Very few that I knew in the latter category were going for anything special. They were mostly out to give this new caliber a halfhearted whirl as opposed to really going for the gusto. A few guys I knew were doing builds that were basically a close facsimile to the Barrett Rec7. And that’s fine if that’s your flavor. But  it is not the best way to fully take advantage of the 6mm ARC cartridge.

What DI rifle in 6mm ARC Should Be

It is my opinion that a DI rifle in 6mm ARC ought to push the boundaries a little, with more jazzed up, highly developed, industry-leading components that contribute to enhancing the 6mm ARC in its primary points of use. Those being:

  1. Precision long range.
  2. And/or shooting from a built-up position.
  3. And as multipurpose AR caliber it must also still be fully capable of making the fight that any capable man could with a purpose-built AR15.

In other words, this 6mm ARC should not lean so hard towards precision/long range that it is no longer suitable for kicking-in doors or being utilized as an impact weapon in a CQC situation.

As I continued to research and consider building my own rifle, I stumbled upon the San Tan Tactical STT-15-6ARC. This rifle seemed to be exactly what I was looking for, with a wide range of features that enhance its performance and versatility.

I was beyond enthused by the specifications of this rifle.

San Tan Tactical STT-15-6ARC

The STT-15-6ARC

STT true matched pillar billet sets, hand finished, matching serial numbers. The upper is cut from a single solid 7075T6 Certified Aerospace Aluminum. Propriety special burnished bore that gives a compacted internal surface, resulting in a much smoother surface finish. The bore, receiver extension face, barrel nut threads, and barrel extension surfaces are all machined in one operation, ensuring that they are perfectly concentric and perpendicular to the barrel assembly.

STT Lower Features:

  • Oversize, 1.38-inch Integrally Machined Magazine Well Flare
  • Ambidextrous Quick Attach Detach Sling Swivel Points with Anti-Rotation Stops
  • Ambidextrous Bolt Release
  • Ambidextrous Magazine Release
  • Bullet Pictogram Safety Selector Markings
  • Set Screw Trigger Creep Adjustment
  • Set Screw Upper Take Down Tension Adjustment
  • Shooter Ready Finger Rest
  • Oversized Winter Trigger Guard Perfect for Gloved Hands
  • Dowel Screw Assembly
  • Ultra-Grip Texture on All Controls

STT Upper Features:

  • San Tan Tactical Truss Pockets for Increased Structural Rigidity
  • Cut from a Single Billet 7075 -T6 Aerospace Grade Aluminum
  • Shell Deflector
  • Fully Assembled with Forward Assist & Ejection Port Cover
  • Machined in T Markings for Easy Optic Relocation
  • Machined with M4 Feed Ramps
  • Machined to Mil-Spec Standards
  • Interfaces with all AR15/M16/M4 Systems & Accessories
  • Compatible with Multiple Rails, Anti-Rotation Tabs & Pins
  • Compatible with All Known Battery Levers
  • No Roll Pin Design – Forward Assist Attaches Via Threaded Dowel Pin

San Tan Tactical STT-15-6ARC Rifle Features:

  • STT Suppressor Optimized Enhanced Bolt carrier group.
  • STT 6 ARC HPT MPI Bolt, Crane O-ring Upgrade
  • Proof Research 18” Carbon Fiber 6ARC Barrel
  • CMC Triggers 3.5lb Single Stage Match Trigger
  • MagPul MOE plus Grip
  • MagPul CTR Stock
  • MagPul MBUS Pro
  • STT 15 16” MLOK Rail
  • Precision CNC machined from billet 7075-T6 certified aluminum.
  • Propriety special burnished bore that gives a compacted internal surface, resulting in a much smoother surface finish
  • Type 3, class 2, deep black, hard coat anodized black.
  • Features extended feed ramps.
  • Ambidextrous Mag and Bolt release controls (ambi version only, not Lite)
  • CERAKOTE options are available for additional cost.

The true matched billet upper/lower sounded impressive. Those 100% ambidextrous controls would come in handy when shooting and reloading from a built-up position. That CMC trigger has an exceptional reputation. The Proof Research barrel was the cherry on top! I pulled the trigger the following day.

First Impressions

Rifle in hand, I was beyond impressed. For starters, the weight straight out of the box. I had never owned an AR-type rifle with a carbon fiber-wrapped barrel. I could hardly believe I was holding a rifle with an 18-inch barrel, given the weight. Then, the millwork. The enchanted trigger guard and magazine well. And the CMC trigger seemed to live up to the hype.

San Tan Tactical STT-15-6ARC

I tossed on the optic and a bipod and set it on the table. Then, just sat for a moment and stared at it. I could not wait to get out to the range with this thing!

But wait I would.

The Wisconsin winter had descended upon us. By the time I got the range time that I needed, I would be giving it my best in the modifier of frigid cold Wisconsin winter temperatures. So, like any Wisconsin boy would, I prepared. Long underwear, heavy boots, layers, warm and extra warm gloves.

Outfitting Optics

Of course, I had kitted the rifle out with a Vortex Razor 1-10. I say of course but I had actually (briefly) considered going with something more powerful. In fact, I did a bit of an optics switcharoo that is probably worthy of its own brief tangent.

Originally, I had outfitted my bolt action 6mm ARC upper with my Vortex Razor 1/10. I reasoned that I only needed that 6mm ARC build to do what it needs out to 1000 yards.

For a moment, it was tempted to think that the San Tan 6mm ARC could push that same round significantly further with four more inches of finely tuned, Proof Research excellence, at my disposal. However, with the San Tan Tactical being a semi auto DI rifle, if I upped the optics magnification capability and/or weight, I would be missing out on the ability to fight with it like a regular AR15.

So, I pilfered the Vortex Razor 1-10 from my highly capable Uintah 15 upper and selected a new optic for it. And I went with the very light weight and capable Razor HD LHT 4.5-22X50 this time. Figuring that maybe it was best after all to go with something that would enhance my capability to self-spot at a distance. And 22X50 would certainly do that.

So, with my optic swap now settled, I was off to the range!


At The Range

Bundled as I was, I decided to bring along a lead sled as I would not be entirely comfortably nor leisurely taking my best shots for an extended period, given the extreme temperature. I had the good fortune of a companion capable of calling my shots and found myself dialed in with just three major and four minor adjustments.

With just over a box and a half of Hornady ELD Match through this outstanding rifle, I measured the last six shots of my final two adjustment at under 1.5 MOA. I was excited now to see what was the truly the BEST that I could do with this fine rifle.

I hung three more targets, opting to preserve the first for frame of reference. On the first target I struck a group that seemed, at a glance, to come a smidge under 1 MOA. I was of course happy with this result but convinced that at least the rifle could do better. So, I engaged the second target, this time with an elevated sense of determination. Two in a row, looking half MOA, I was excited. Just as the third shot rang out, I was startled by a barrage of cursing from my range mate. I thought he had been injured given his cursing, but no, he had spilled a warm mug of coffee directly into his range bag. I put my eye back to the glass and that third shot did not live up to my hopes or expectations. So, I broke from the rifle and assisted in addressing the coffee calamity with some rags from the back of my truck.

Target shot with San Tan Tactical STT-15-6ARC

The temperature was dropping, so I decided to warm up. A few minutes later, I returned to the bench my hopes set on smashing the third target with a group worthy of both the rifle and my own capability. And three shots later, the rifle and I had definitely produced that group.

As my friend on the other side of the firing line was still doing his work, I gazed through the glass imagining how tight that grouping was. It looked at least .7 or could it be .55, maybe better? I was as happy and satisfied as I could be. And I began to gather up my gear. Then I noticed a magazine from earlier when my counterpart took a turn on the STT-15. I had given him five rounds and he graciously took only three. The magazine still had two rounds left in it.

So, I shot them. I took aim at the target and in making a decision not to muddy the perception of my impeccable grouping, I took aim at the number 8, towards the targets left outer rim. Pop, pop. and produced what seemed a hole indiscernible as two. I will admit that I looked twice. I did not feel that I had thrown the second round. but if I had I could not have thrown it that far. I did not throw it, I knew that. But I was so in awe of having laid those two rounds so upon one another as I did with so little thought or extraordinary effort.


Target fired with San Tan Tactical STT-15-6ARC

And that was the immensely satisfying wrap up to my first STT-15-6ARC experience. I now had the option of a full size, incredibly light weight, precision long range, combat ready, plus serious bells and whistles rifle in 6mm ARC and I could not find a complaint about it.

If you are at all enthused about this new cartridge, I highly recommend going the distance with a company that has gone the distance already on your behalf and has systematically designed and produced a platform that will go the distance for you! Everything that the 6mm ARC is capable of can be realized by the STT-15-6ARC. I promise you that.

In short,

After thoroughly researching and considering various options, I have come to the conclusion that the San Tan Tactical STT-15-6ARC is the best choice for a semi-auto, direct-impingement (DI) rifle in 6mm ARC. This rifle offers a perfect balance of precision and versatility, with a range of features that enhance its performance and suitability for a wide range of shooting applications. If you are looking for a rifle that truly pushes the boundaries of what a DI rifle in 6mm ARC can be, then the STT-15-6ARC is the one for you.

For more information on San Tan Tactical, please visit –

STT-15 6ARC 18″ Rifle+ Gas 6mm ARC – Black Anodize