San Tan Tactical STT-15-6ARC (Photo: San Tan Tactical)
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It just might be a first in the gun industry. For once, an ammunition manufacturer launched a new cartridge ahead of schedule and a firearms manufacturer launched the accompanying rifle early, too. That’s how the 6mm ARC and the San Tan Tactical STT-15 6ARC hit the market. And after shooting the rifle I can say they did well – and that I want one for an in-depth review.

The STT-15-6ARC rifle alongside Hornady 6mm ARC ammo at the range

The 6mm ARC as described by Hornady, its creator:

Tested, selected, and fielded by a specialized group within the U.S. DoD for its multipurpose combat rifle program, the versatile 6mm ARC does much of what larger cartridges can and everything that smaller cartridges can’t. Designed to meet the needs of the world’s toughest critics, the 6mm ARC utilizes efficient, high-BC bullets to deliver unprecedented performance from the AR-15 platform. Commercial 6mm ARC offerings will feature bullets selected to deliver ideal performance for hunting, match shooting, and personal protection applications.

Let’s get a couple of the obvious questions out of the way. According to the Hornady their 6mm ARC outdoes .223 Rem by a lot — not a big surprise — and, of course, outdoes .308 Win, too. They also say it’s a stronger long-range performer than 6.8 SPC.

The rep from San Tan said the new cartridge has a flatter trajectory and greater velocity than the .224 Valkyrie. Does all this mean the 6.5 Creedmoor fanbois may have some competition in the cartridge popularity contest market? Maybe.

Wouldn’t that be fun to watch play out?

The Rifle


There’s a list of manufacturers making 6mm ARC-chambered rifles but I got to shoot San Tan Tactical’s last week. One thing that appeals about this specific model is that Proof Research got in on it with one of their 18-inch carbon fiber barrels. But it’s also clear a lot of thought went into the specs of this rifle (see below).

The rifle the STT rep had along with him was the Black Multicam CERAKOTE version which is unsurprisingly a popular choice. Without a scope the rifle weighs under 7 lbs, making the final weight your choice depending on the scope you use.

The 6mm ARC ammunition fits in standard AR-15 mags which is nice considering the massive assortment of “look at this boutique round” mags I have in boxes in my gun room.

A full review of this rifle is definitely needed, but at first blush it appeared well-made, reliable, and accurate. The 3.5 lb. single-stage trigger has a clean, crisp break and short reset, the rifle itself is lightweight and shoulders comfortably, and I’d like to run it long-range and see what it can really do. I also want to break out the chronograph and compare it to some of the other popular and/or recent long-range cartridges.

I’m always a little leery of The Latest Hotness cartridges, but given the source — Hornady — I think this one is worth trying out at length. And if you’re wondering about STT — maybe you’ve never heard of them — they’re part of the CMC Triggers family, a manufacturer whose products I’ve liked for a long time.

Let’s hear it, guys. Predictions?

STT Lower Features:
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 Reset
Oversized Winter Trigger Guard Perfect for Gloved Hands
Dowel Screw Assembly
Ultra-Grip Texture on All Controls
Weight: 9.4 ounces

STT Upper Features:
San Tan Tactical Truss Pockets for Increased Structural Rigidity
Cut from Single Billet 7075-T6 Aerospace Grade Aluminum
Shell Deflector
Fully Assembled with Forward Assist and 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 and Accessories
Compatible with Multiple Rails, Anti-Rotation Tabs and Pins
Compatible with All Known Battery Levers
No Roll Pin Design – Forward Assist Attaches via Threaded Dowel Pin
Weight: 8.2 ounces

STT-15-6ARC Rifle Features:
STT Suppressor Optimized Enhanced Bolt Carrier Group
STT 6ARC HPT MPI Bolt, Crane O-Ring Upgrade
Proof Research 18-inch 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-inch MLOK Rail
Precision CNC Machined from Billet 7075-T6 Certified Aluminum
Proprietary 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
CERAKOTE options available for an additional cost
Total weight: 6lbs, 13 oz

Complete Rifle MSRP: $2,895

Check it out here.


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    • I’d be surprised if you can’t get one. Their STT-15 lower and parts kits are fully ambi. Their founder is a lefty, and a big part of their founding vision was to design an optimal, deluxe ambi lower. They’re local to me, and I built a rifle on their lower. Everything about the design is well thought out and premium.

      Anyway, email them and ask about getting that rifle in an ambi configuration. Plenty of pics on their site of the STT lower with their unique parts kits.

  1. Not being a rifle guy, how is 6mm a better round than 7.62mm? If bigger is better, how is 6mm better than 7.62?

    (I noticed that, unlike 6.5 Grendel, the 6mm round does not vaporize its target, nor send it into a completely new dimension of time and space, so we can’t ignore that.)

      • Thanx for the link; informative.


        It runs counter to the mantra the “bigger is always better” when it comes to bullets.

      • Probably the most relevant part for the vast majority of MSR owners:
        “For tactical applications and varmints inside 300 yards, the .223 Rem. probably remains the best option. The vast selection of purpose-built loads, combined with its higher magazine capacity, make it the undisputed king for those applications.”

    • Well you are gaining 500fps shooting the same bullet so I see why you would be loathe to change.

      What is your magazine capacity like and what kind of barrel life are you getting?

      • I fit 8 in a modified pmag 30rnd. Don’t know the barrel life yet. I just started shooting it 2.5 years ago and then moved and haven’t shot it since. I only worked up one load that was intended to be moderate on the barrel. It pushed 82gr copper flatbase bullets to just under 3,400fps. According to QuickLoad’s guestimate it only hit 48kpsi, had the max pressure at 3″ bullet travel and the pressure curve was also very gradual as pressure curves go. I must admit that I am much more of an experimenter than a practical shooter. I used a mid weight bullet because my interest was in high velocity at 200-300m and not long distance shooting. Work and unfortunate events have kept me from shooting it more yet. Hopefully I will try a heavier lead bullet before the collapse of civilization.

        • I think I had expected to get 11 rounds in pmag 30. I can’t remember why. I don’t think about it anymore though because 8 is fine for my purposes.

  2. Kat,

    Thank you for including the MSRP .

    Looking forward to your more in-depth review.

    That kind of scratch is difficult for many of us retirees to justify…but, hey, I can dream of owning one.

    • They make a lot of very contextual claims and then don’t specify the context. Standard marketing tactics. It’s a lot like lying.

      • See the link above I linked to. Some good reading on that.

        I’m not selling, endorsing, representing, etc. just food for thought.

        • Thanks, my comment came off harsher than I intended. I suspected that the claims were generally true but I am super anal about context. I do appreciate the round too.

    • Every new round that comes out, “out does .308…” supposedly… hypothetically… maybe… ok sometimes… with the right barrel… and wind…

      • 6mm PRC, 6.5 CM, 6.5 Grendel, 6.8 SPC, .350 Legend, .458 SOCOM, .50 Beowulf, etc. etc.

        So many boutique cartridges now. The field is getting a bit crowded.

        • “So many boutique cartridges now. The field is getting a bit crowded.”

          Yeah, but you gotta consider….each one is better than all the others.

  3. One of the things the military wanted was better armor penetration at distances. None of these do it.
    It’s a interesting cartridge but so was the Valkyrie at first.
    When it was released we asked a lot of questions none of which were answered. We asked for hunting videos none of which were seen because they didn’t do any. We asked about the armor penetration and yup “crickets”.
    This means it wasn’t vetted just built, produced and wholla the new magic and as soon as we can claim SOCOM used it the better for marketing.
    It makes me leery

    • I think that the 6 gets better drop and drift however I think the Grendel is going to be a better hunter at close to midrange (500). I’m guessing that’s why they were so hesitant to answer our questions.

        • Yes it does. My 6.5 Grendel journey is just starting but the cheaper wolf actually shoots best at 100 lol. I’ll try it to 500 soon.
          I can’t wait for November to deer hunt with it.

  4. 6mm has as larger variety of bullets with greater sectional density, 6.5 more limited.
    Just got off the range this morning with my Brownell’s Faxon 20″ 1:8 and CMMG 20″ 1:7.5 6mm ARC rifles DIY 80%. They work very nice plus I have a lot of 6mm bullets to support them and my 6mm Creedmoors. I do have 6.5 Creedmoor’s as well. These 6mm ARCs are just so much lighter and easier to handle. Thank you Texican for your 6.5 Grendel bolts and magazines they work fine in the 6mm ARC. A fair chunk of SOCOM lives in my backyard, don’t hear any of them complaining. My cold bore with the Faxon hit the upper right quadrant of my aim small miss small orange dot target. Don’t have much to say about specific article brand but idea works for me.

  5. ” According to the Hornady their 6mm ARC outdoes .223 Rem by a lot — not a big surprise — and, of course, outdoes .308 Win, too. ”

    The 6mm ARC does have a flatter trajectory than the .308 Win (of which there is little value in the day of the LRF and ballistic reticles) and slightly better wind (of which there is a lot of value).

    But “outdoes?” Not even close.

    Using Hornady’s data, out of rifle with the same barrel length, the most powerful 6mmARC round generates less than 1k ft/lbs of energy at 350 yards. Their .308 Wins do that out to about twice that distance. The 6mmARC never catches up.

  6. The way things are headed in November I wouldn’t waste my money on semiautomatic rifles or double stack pistols. The later are going to be confiscated or NFAed and we are going to see a national 10 round cap. Time to make sure you have the right single stacks, revolvers, bolt guns and shotguns.

      • We will see about that. One thing is certain you won’t be seen in public with them. Cops are lazy they will go after low hanging fruit. Thanks for providing cover.

        • You were supposed to support mass non-compliance. Instead, you rushed to be an obsequious subservient subject. Obedient and servile. And it looked pathetic. And emasculated. And I’m feeling bad your resolve is so shallow.

        • TD, I’m not just an internet tough guy, I’m a real life tough guy, and I’ve got a lifetime of experiences to prove it.
          As an internet coward, and a real life one too, I’d expect you to understand that.

        • Correct but they will grab the internet tough guys like JW.

          Here is a pro tip in the form of a question: How did the Russia beat both Napolean and Hitler?

        • TD, perhaps you are as poor of a historian as you are a patriot.
          Russia won by employing a massive scorched Earth policy in both wars, including sacking their own cities. Against both Napoleon and the Nazis, they refused to surrender cities even when the losses would be obvious, often choosing instead to burn down the cities around themselves.
          They did not tolerate cowards. You would have been culled quickly.

    • Dude, obviously your balls haven’t dropped out of your cunt. Get the right single stacks?! FOR WHAT?! Not like you’re gonna do shit! If you’re scared of having a double stack and want to get single stacks because “they will be allowed”, you won’t have the balls to use the single stack when the time comes! Because you don’t have the balls to use a double stack in the first place!

    • Ho hum. Another leftist shill posing as a gun owner. Whatever dude. You’re a dime a dozen. Or you’re all the same guy. Either way it’s sad.

  7. ….And of course ammo is readily available in stock and in plenty of variety like .223 and .308 at comparable prices.

    Uh, no. It’s probably going to be a reloader round for a while. But if you’re paying 3K for a gun your not worried about the price of ammo. Availability hits everyone but since this is a niche round there is probably a lot of stock on the shelves. Other rounds like 300AAC were formed from existing stock and you could even cut your own brass to spec.

    Can’t wait to see it try to dethrone .30 cal rounds for damage at a distance. Physics of energy beats cross sectional density or whatever they come up.
    The DoD should just stick with .308 and be done instead of looking for compromise solutions that check boxes no one really cares about. The .308 is a proven performer warts and all and it gets the job done.

    • Many military committees have decided 7mm is the optimum calibre but not many actually followed through with adoption.

  8. I like to see new cartridges come out. Ammo manufactures coming up with new designs. That is all well and good.

    But fact is, I cannot keep up with the new round of the month.
    The 6ARC, looks great. The numbers are great.

    Fact of the matter is, I had to settle on one round that can do most everything well. From coy, ground hogs, white tail deer, to black bear. And the possible two legged critter.

    What was readily available before COVID hit, and cheap and fits all that?
    The lowly 308WIN.

    I can, and have, reloaded it for varmint, to deer to bear sized game. Loads for short brush, to medium ranges across open fields. I can have anti-material rounds at medium distances for my particular location.

    I envy those of you who can drop a few hundred to thousand for the cartridge of the month club.
    The rest of us, have to make do with what makes sense and we can afford.

    • I standardized on .308 years ago. So many guns are offered in this versatile caliber and ammo ranges from surplus to match grade. Reloading opens up a world of possibilities too.

      • Just recently, though I looked into and should of done it awhile ago, cast bullets.
        Cannot find any in stock in 308WIN for the 150 to 170grns.
        Looking for something that can put meat on the table and put the two legged critters down.
        Might not punch through body armor, but put a good hurting on them. And, POA being MOG (Minute of Groin) still put them down.

    • There is nothing wrong with your .308 for everything approach. I just don’t see why you have to have only one cartridge for everything. Couldn’t one just have an AR15 in 5.56 for defense and varmints, and then a basic bolt action in .308,.270,6.5CM, 30-06 for larger game or longer range? That is what I’ve done .270 bolt action and 5.56 AR.

      • ” I just don’t see why you have to have only one cartridge for everything. ”

        Why not? .50BMG pretty much serves all needs.

  9. The advantage of 5.56 is capacity, weight, and low recoil.

    This seems to trade away most of those advantages – so yeah, it’s more powerful and better at long range, if that’s what you’re looking for.

    • The advantage to 5.56 is the easy availability. Nothing else.

      Sure it will get the job done, but so will a .22lr. Not the point.

      Its more efficient. Its not going to take 1 5.56, round its going to take take 3…4…5…6. The grendel/ARC 1…2 maybe. That negates any ammunition loss.

      Magazine issues? Test and be confident, there are ones that work just as well for 6.5g/ARC. If 7.62×39 with the aggressive taper can be made to feed reliably (which ASC and CPD have both done) then a mag that needs different lip angle and a bit wider than 5.56 is no challenge to make run well.

      How about distance? You ever see a 62gr vs a 100gr hit over 300 yards on a full size ipsic? The 556 doesnt move the target. The grendel on the other hand shakes it and the camera on impact at same recording distance. Real world physics not second or third hand bs.

      But who am I? Keep getting that 223/556 for 50, 60 or 70 cents though and leave the ‘not better cartridges’ for the dummies.

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