Precision Reflex Mk12 Mod 0 Spr Gen Iii 5.56Mm 18'' Bbl 1-7 Twist Upper Black

The Precision Reflex Mk12 Mod 0 SPR upper receiver is a complete, ready-to-run 5.56 NATO upper built for shooters who demand serious precision rifle capability. Built around an 18" Douglas 416 stainless steel barrel with a 1-7 twist rate, this upper delivers the accuracy and velocity balance that made the original Mark 12 Designated Marksman Rifle a favorite among professionals and long-range hunters. Whether you're assembling a precision rifle from scratch or upgrading an existing lower, this Gen III upper gives you a field-proven platform without the guesswork.

This is a complete upper assembly—not a stripped receiver. It arrives with all the hard parts already fitted and headspaced: a flat-top upper receiver, rifle-length gas tube system, and a Full Auto bolt carrier group (compatible with any standard AR lower receiver). The barrel is precisely chambered in 5.56 NATO, ready for both commercial and military ammunition. The gas system is optimized for the 18" barrel length, so you get reliable cycling without over-gassing or unnecessary bolt speed.

The Mk12 Mod 0 SPR Gen III configuration includes a rifle-length carbon fiber free-float forearm—eliminating barrel contact with the handguard to maximize accuracy—plus a full-length integrated top rail with a removable PEQ II section. You get PRi-brand flip-up iron sights (front gas block sight and rear sight) for emergency holdover shooting, a Gas Buster charging handle with oversized latch for gloved operation, and muzzle brake and collar. Finished in durable black, this upper is sealed and ready to run out of the box on any standard AR-15 lower receiver you pair it with.

The Mark 12 platform is proven across decades of military and civilian use for medium-to-long-range precision shooting—hunting, competition, and patrol work. If you need a rifle-length gas system, 18" barrel accuracy, and serious rail real estate without building a complex upper from scratch, this is a faster, more reliable path to a working precision rig.

Key Features

• Complete, ready-to-shoot 5.56 NATO upper assembly—arrives fitted and headspaced
• 18" Douglas 416 stainless steel barrel with 1-7 twist for reliable accuracy and velocity
• Rifle-length gas system and Full Auto bolt carrier for consistent, reliable cycling
• Carbon fiber free-float forearm isolates barrel from handguard contact for improved accuracy
• Full-length integrated top rail with removable PEQ II rail section for optics and accessories
• PRi flip-up iron sights (front gas block and rear) for rapid-fire emergency use
• Gas Buster charging handle with large latch for easy manipulation in combat gloves
• Muzzle brake and collar included
• Flat-top upper receiver for maximum mounting flexibility
• Durable black finish

Specifications

Frequently Asked Questions

What lower receiver will this upper fit?

This Mk12 Mod 0 upper is a standard AR-15 upper assembly that pairs with any AR-15 lower receiver. The Full Auto bolt carrier is compatible with any standard AR-15 lower, whether semi-auto or full-auto capable on the lower side.

Is this upper complete and ready to shoot?

Yes. This is a fully assembled upper receiver—it arrives fitted, headspaced, and ready to run. You only need to attach it to a lower receiver (which includes the trigger group, magazine well, and buffer system) to have a complete, functional rifle. All gas tube, bolt, barrel, rail, sights, and charging handle are installed.

What's the accuracy advantage of the free-float handguard?

The carbon fiber free-float forearm does not contact the barrel, which eliminates a major source of accuracy variation. When the barrel is free to vibrate consistently without pressure from the handguard, you get more predictable shot placement, especially important for precision rifle and designated marksman work at distance.

Can I use commercial 5.56 or military ammunition in this barrel?

Yes. The 5.56 NATO chamber accommodates both standard commercial 5.56 ammunition and military-spec 5.56 rounds. The 1-7 twist rate is suitable for a wide range of 5.56 bullet weights and is commonly used for both light and heavier projectiles.