The PWS MK118 MOD 1-M Complete Upper (PWS part no. MK1M1U6ARC18NC) is an 18-inch, 6mm ARC upper built around Primary Weapons Systems’ Long Stroke Piston gas system instead of direct impingement. The ambidextrous upper receiver is machined from 7075-T651 forged aluminum without a forward assist, and the 1:7.5-twist barrel is threaded for a muzzle device. PWS backs every complete upper with a sub-MOA accuracy guarantee when paired with quality ammunition and sound fundamentals.

Key Specifications

• Chambered in 6mm ARC.
• 18-inch barrel length.
• 1:7.5 twist rate.
• PWS Long Stroke Piston gas system, adjustable across 3 gas settings.
• Ambidextrous upper receiver machined from 7075-T651 forged aluminum, built without a forward assist.
• Weighs approximately 5 lb (upper only).
• Threaded muzzle for a muzzle device.
• Backed by PWS’s sub-MOA accuracy guarantee with quality ammunition.

Frequently Asked Questions

Does this upper have a forward assist? No — the MOD 1-M is built without a forward assist, distinguishing it from PWS’s standard MOD 1 upper.

What twist rate does this barrel have? 1:7.5, tuned for the MOD 1-M’s 6mm ARC chambering.

Does this include a bolt carrier group and charging handle? Yes — as a complete upper, it ships with the bolt carrier group and charging handle installed, ready to drop onto a compatible AR-15 lower.

Buy the PWS MK118 MOD 1-M Complete Upper, 6mm ARC, 18in, Long Stroke Piston

Order the PWS MK118 MOD 1-M Complete Upper, 6mm ARC, 18in, Long Stroke Piston from a Lubbock, TX gun shop. Shop more PWS gear or browse the AR15 uppers category at Schaefer Defense.