Primary Weapons Systems MK1 5.56x45mm AR Lower, Black - 18M100RM1B
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Primary Weapon Systems
Overview
The Primary Weapons Systems MK1 5.56x45mm AR Lower is a complete lower receiver designed for the AR-15 platform, featuring a hardcoat anodized finish in black. This lower is specifically calibrated for the 5.56 NATO cartridge and includes a trigger pin diameter of .154, ensuring compatibility with most standard AR-15 triggers. Builders often use this lower in 5.56 NATO caliber builds, making it a versatile choice for a range of applications.
Specifications
Primary Weapons Systems MK1 5.56x45mm AR Lower, Black - 18M100RM1B
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Build history on GunPartPicker
Builders on GunPartPicker first added the Primary Weapons Systems MK1 5.56x45mm AR Lower, Black - 18M100RM1B to a build in February 2026.
Updated · from real builds on GunPartPicker
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