PWS MK118 MOD 2-M 6mm ARC 5/8 X 24 - Complete Upper - 18"

When you want piston-driven precision in 6mm ARC from a complete upper optimized for long-range performance, the Primary Weapons Systems MK118 MOD 2-M 6mm ARC 18" upper delivers the PWS Long Stroke Piston System, 3-setting Adjustable Gas System, and sub-MOA guarantee in a 5-pound package threaded 5/8-24 for popular 6mm and .308 caliber muzzle devices.

The Primary Weapons Systems MK118 MOD 2-M 6mm ARC is a complete upper receiver assembly designed for precision shooters and hunters who want the 6mm ARC cartridge's long-range ballistic advantages in a piston-driven, suppressor-optimized upper that drops directly onto any mil-spec AR-15 lower receiver.

The 6mm ARC was purpose-built for the AR-15 platform to deliver long-range performance — exceptional ballistic coefficients, flat trajectories, and superior retained energy at extended distance compared to 5.56 NATO. The PWS Long Stroke Piston System keeps the upper receiver group cleaner and cooler through suppressed and sustained fire, and the 3-setting Adjustable Gas System allows precise fine-tuning for standard and suppressed use without tools. The 18" barrel with 1:7.5 twist is optimized for the full spectrum of 6mm ARC ammunition types, and PWS backs this Boise-made precision barrel with their sub-MOA accuracy guarantee using high-grade ammunition. The ambidextrous upper receiver from 7075-T651 forged aluminum — designed without a forward assist — incorporates the PicLok handguard that combines Picatinny and M-LOK for versatile accessory mounting. The 5/8-24 muzzle thread accommodates the broad ecosystem of 6mm and .308/7.62 caliber muzzle devices and suppressor mounts. The Radian Raptor ambidextrous charging handle ensures reliable operation for any shooter. At 5 lbs, the MK118 upper keeps the overall rifle weight manageable for extended field carry.

Caliber: 6mm ARC. Barrel: 18", 1:7.5 twist, sub-MOA guarantee. Muzzle thread: 5/8-24 (muzzle device not included). Gas system: PWS Long Stroke Piston, 3-setting adjustable. Receiver: forged 7075-T651 aluminum, ambidextrous design. Handguard: PicLok (Picatinny + M-LOK). Charging handle: Radian Raptor ambidextrous. Weight: 5 lbs. Compatible with mil-spec AR-15 lower receivers.

The ambidextrous 7075-T651 forged aluminum receiver eliminates the forward assist for a cleaner profile while retaining the precision fitment that mil-spec compatibility demands. The 3-setting adjustable gas system delivers straightforward suppressor optimization without additional hardware.

An excellent complete upper for precision 6mm ARC builds — particularly for long-range hunting, precision rifle competition, and suppressed use where the 6mm ARC's efficiency and the PWS piston system's clean operation provide a decisive advantage.

Backed by the PWS VOW — Primary Weapons Systems' warranty guaranteeing repair or replacement for any manufacturing defects. Precision manufactured in Boise, Idaho, USA.