The PWS MK1 MOD 1-M is a complete AR-platform upper built around PWS’s long-stroke piston system, chambered in .223 Wylde with a 14.5-inch barrel and PWS’s Long-Stroke (LS) thread pattern (PWS part no. MK1M1U22314NC). The .223 Wylde chamber lets the upper run both .223 Remington and 5.56 NATO ammunition, and the anodized barrel finish matches PWS’s other MK1 uppers for a consistent look across a build. Like the rest of the MK1 line, it uses PWS’s piston operating system for cleaner, more consistent cycling than a direct-impingement gas system. This upper ships complete and ready to mate to a compatible AR-platform lower.

Key Specifications

• It is chambered in .223 Wylde, allowing both .223 Remington and 5.56 NATO ammunition to be fired safely.
• The barrel measures 14.5 inches, matching this specific MK114 configuration.
• It has a 1:8 twist rate, matched to common .223/5.56 bullet weights.
• The barrel is finished in anodized coating for corrosion resistance.
• It uses PWS’s long-stroke piston system rather than direct impingement, for cleaner-running operation.
• It ships as a complete upper, ready to mate to a compatible AR-platform lower.
• It ships as an upper receiver group only, without a lower receiver, requiring a compatible AR-platform lower to complete the rifle.
• It is built under PWS’s MK114 model designation, part of the MK1 MOD 1-M family.
• The 14.5-inch barrel is a common length paired with a pinned-and-welded muzzle device to reach the legal 16-inch minimum for a rifle-configured build.

Frequently Asked Questions

Is this upper regulated like a short-barreled rifle? No. This is a bare upper receiver group sold without a lower receiver. Barrel length only becomes an NFA/SBR consideration once the upper is mated to a shouldered rifle-configured lower; paired with a pistol lower or braced pistol build, different rules may apply. Confirm your specific lower configuration meets current ATF rules before assembly.

What ammunition can this upper safely fire? It is chambered in .223 Wylde, which safely fires both .223 Remington and 5.56 NATO ammunition.

What operating system does this upper use? It uses PWS’s long-stroke piston system rather than a direct-impingement gas system.

Buy the PWS MK1 MOD 1-M Complete Upper, .223 Wylde, 14.5-inch

Order it directly from our Lubbock, Texas gun shop for fast, insured shipping to your door. Shop the full PWS lineup and browse our AR15 uppers selection for more build components.