New 6 mm ARC (Advanced Rifle Cartridge) and STT-15-6ARC Rifles

From San Tan Tactical

San Tan Tactical, Hornady and Proof Research have partnered up on the San Tan new 6 mm ARC rifles. San Tan’s high-quality firearm systemsin combination with Hornady’s New 6 mm ARC round originally developed for a specialized group within the US DoD, and Proof Research premium carbon fiber barrels take the AR-15 platform to a whole new level!

The Hornady 6 ARC Round

Hornady provides world-class performance in a 6 mm ARC factory-loaded cartridge. The high-performance, match-accurate round features an excellent cartridge-to-chamber relationship and shoots exceptionally well. The 6 mm ARC is commercially available in 108-grain ELD-MATCH, 105-grain BTHP BLACK, and 103-grain ELD-X -Precision Hunter loads. The ELD-Match round boasts a G1.536 BC.
6 mm ARC Advanced Rifle Cartridge

Tested, selected, and fielded by a specialized group within the US DoD for its multi-purpose combat rifle program, the 6 mm ARC is an extremely versatile cartridge that does everything much larger cartridges can, and everything that smaller cartridges can’t. Designed to meet the demanding needs of the world’s toughest critics, the 6 mm ARC is a truly advanced cartridge capable of utilizing high BC, efficient 6 mm bullets for unprecedented levels of performance from such a compact platform.

AdvancedPurpose-built to achieve performance never before delivered from the AR-15 platform by providing the ultimate blend of system weight, performance and shootability. 

VersatileEqually at home in AR-15 platforms and short or micro action bolt guns and suitable for a variety of applications from personal defense, match shooting, hunting as well as military and law enforcement use.

Efficient –Balanced application of cartridge and chamber geometry & interface, propellant design, and bullet selection for optimum performance and barrel life, the 6 mm ARC has unmatched long-range performance from the AR-15 or micro action platform.

EffectiveExcellent terminal performance from an assortment of bullet selections, for a variety of applications.

• Features match accurate Hornady bullets that are held to the tightest tolerances in our test lab

• Low recoil

• Flexible

• Utilizes an efficient propellant charge and bullet weight combination

• Less felt recoil than larger short-action-based cartridges

• Factory ammunition in a variety of bullet styles may be complemented by the handloader who has a multitude of 6 mm bullets to choose from for specialized applications

CMMG also announced rifles in the chambering. Here’s a link to more info.

Hornady Loads

6mm ARC 108gr ELD-MATCH 
Muzzle Velocity = 2750FPSwith 24″ test bbl
G1 BC = .536
SD = 261
Min Twist Rate = 1-8”

6mm ARC 105gr BTHP BLACK 
Muzzle Velocity = 2750FPSwith 24″ test bbl

G1 BC = .530
SD = 254
Min Twist Rate = 1-8″

6mm ARC 103gr ELD-X -Precision Hunter 
Muzzle Velocity = 2800 FPS with 24″ test bbl
G1 BC = .512
SD = 249
Min Twist Rate = 1-8

The Proof Research 6 mm ARC Carbon Fiber Barrel

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 San Tan Tactical STT-15-6ARC rifles are a superb example of industry-leading technologies from companies pushing the envelope with a desire to achieve more! With the other wildcat caliber’s coming to market over the recent years, the recent 6.8 military requirement, all in an attempt to pursue the maximum output from the AR-15 platform.

The Hornady 6 mm ARC cartridge combined with its variety of projectiles currently available allows a significant increase in capability above and beyond what is currently available in the AR-15 platform. The capability to weight savings is seen in out STT-15-6ARC-Lite, the slick sided billet matched receiver set without signature lightning pillar cuts. Removing as much weight as possible without sacrificing strength and performance.

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 Upper Features:

  • STT 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 

STT Lower Features:

  • Huge 1.38” 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 Control

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

Here are full details on the cartridge from Hornady. Lantac also has a rifle chambered for the cartridge, and so does CMMG.

If long-distance is your thing, I interviewed several experts and they had some surprising tips.  

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