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San Tan Tactical, Hornady, Proof Research Team Up for 6mm ARC Release with STT-15 Rifle

The 6mm ARC hit the ground running in 2020 by being as mysterious as possible. SAAMI accepted it in March, and there was limited information regarding its purpose. The story goes that a select group chose it within the DoD for testing in the multipurpose rifle program. At the time, it seemed like no one was actively manufacturing the round. That changed as we learned today, Hornady is charging full steam ahead. 

Hornady partnered with San Tan Tactical and Proof Research to produce a rifle worthy of such a capable round. The 6mm ARC is designed to be more precise and more powerful than the 5.56. It also sheds the recoil, size, and weight of 7.62 NATO. The 6mm ARC delivers more power and penetration and has a longer effective range than the 5.56 could ever hope to.

The San Tan Tactical rifle is more than just a standard AR 15. The STT-15-6ARC features a billet upper and lower receiver, a magazine well with a massive flare for quick reloads, an oversized trigger guard, ambidextrous magazine and bolt release, and more. 

We know Hornady makes good ammo, but a round can't reach its full potential without the right platform. Proof Research is famed for its lightweight, carbon fiber barrels that deliver outstanding accuracy. The new 6mm ARC rifle is equipped with an 18-inch carbon fiber barrel with a 1:7.5 twist rate. 


The STT-15-6ARC is complete with a suppressor optimized BCG, a CMC triggers 3.5 lb single-stage trigger, a Magpul MORE pistol grip, Magpul CTR stock, MBUS pro sights, and an STT 16-inch M-LOK rail. 

This combination from Hornady, Proof Research, and San Tan Tactical looks to be extremely promising. Stay tuned as we learn more about the 6mm ARC, and we see what it can do from the amalgamation of Hornady, Proof Research, and San Tan Tactical. 

Hornady 6mm ARC Load Details

6mm ARC 108gr ELD-MATCH (81608)

  • Muzzle Velocity = 2750FPSwith 24″ test bbl
  • G1 BC = .536
  • SD = 261
  • Min Twist Rate = 1-8”

6mm ARC 105gr BTHP BLACK (81604)

  • Muzzle Velocity = 2750FPSwith 24″ test bbl
  • G1 BC = .530
  • SD = 254
  • Min Twist Rate = 1-8″

6mm ARC 103gr ELD-X -Precision Hunter (81602)

  • Muzzle Velocity = 2800 FPS with 24″ test bbl
  • G1 BC = .512
  • SD = 249
  • Min Twist Rate = 1-8

6ARC Carbon Fiber Barrel Details

The STT-15-6ARC and STT-15-6ARC-Lite both are configured with industry leading Proof Research® Carbon fiber barrels. Known synonymously for their quality, ultra lightweight characteristics and superior accuracy. Featuring a 6ARC Chamber,18” Length, 7.5 Twist, Rifle gas, .750 diameter gas block.


The Hornady 6 ARC cartridge combined with Hornady's variety of projectiles significantly increases the capability of the AR15 platform. The weight savings is seen in the STT-15-6ARC-Lite, the slick sided billet matched receiver set with San Tan Tactical's signature lightening pillar cuts removing as much weight as possible without sacrificing strength and performance.

The STT-15-6ARC features true matched pillar billet sets, hand finished and with matching serial numbers. The upper is cut from a billet of 7075T6 certified aerospace aluminum. The sets also have a proprietary, 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, hardcoat anodized black
  • Features extended feed ramps
  • Ambidextrous Mag and Bolt release controls (ambi version only, not Lite)
  • CERAKOTE options are available for additional cost

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