San Tan Tactical, Hornady and Proof Research join forces to make an AR-15 carbine chambered for the new 6 mm ARC (advanced rile cartridge) ammunition measuring 6x38 mm. The STT-15-6ARC is to provide effective and accurate fire at targets at distances intermediate between the characteristics offered by the 5.56x45 mm and 7.62x51 mm rounds, while maintaining small dimensions and weight.
The 6 mm ARC rounds was given the SAAMI standard in March this year. Interestingly, it seems to be based on 5.6×39 mm ammunition casing (.220 Russian), similar to the 6.5 Grendel or the 6 mm PPC. The overall length of the round is very close to the 5.56x45 mm and is the 57.4 mm rounds and fits standard M16/M4/AR-15 magazines. The muzzle velocity of the 108 gr projectile, according to SAAMI, is 823 m/s. The maximum average pressure is to fluctuate just below 3600 BAR.
Now we know that the American giant, Hornady, took up the serial production of the 6 mm ARC ammunition and, in cooperation with San Tan Tactical and Proof Research, the STT-15-6ARC carbine developed around this caliber was created. The weapon is based on the AR-15 design and from the outside does not stand out with anything special (apart from the Cerakote camouflage, i.e. a high-hardness thermosetting ceramic paint). The Cerakote treatment is made only to order, the standard carbines come in anodized black coating.
The STT-15-6ARC-Lite carbine is equipped with a super-light 18-inch Proof Research barrel with a 1: 7.5-inch twist rate. Its characteristic feature is the design based on a thin steel barrel closed within a carbon fiber sleeve. This allows the production of a low-weight barrel which still has good stiffness and precision. The gas port was placed in a rifle position, with the gas block being 0.75 inch in diameter. This system should ensure a high culture of work. The barrel ends with a standard A2 "Birdcage" flash hider.
In the STT-15-6ARC, has an M-Lok standard handguard with ports on seven planes and a top MIL-STD M19-15 rail (Picatinny), extending the section located on the upper receiver. The receiver also has a mobile assembly optimized for cooperation with a silencer, which in combination with a long barrel and ammunition seems to indicate that the carbine is to act as a marksman weapon. This fact is also indicated by the use of an adjustable, single stage CMC Triggers mechanism in the lower receiver with a resistance of just 1.6 kg.
The receiver is made of 7075-T6 forged aluminum block. It has many weight-reducing features and an extended trigger guard, ribbing in the front of the magwell and a built-in funnel. In the rear part of the lower receiver there is a central attachment point for the QD carrying sling swivel mount. Other accessories that can be found on the weapon are Magpul MBUS Pro iron sights, the CTR stock and the MOE+ grip from the same manufacturer. In the standard (not Lite) version, all manipulators were double sided and can be used by right and left handed shooters.
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Interestingly, San Tan Tactical does not specify the magazine capacity. The set includes a standard 30-round PMag Gen M2 that holds 30 5.56x45 mm rounds, but it is not known how many 6 mm ARC rounds, which have a slightly larger casing diameter, can those magazines hold. The price of weapons in both variants is 2985 USD.
