TacFire AR Build Kit 5.56x45mm NATO 7.50" Barrel Black for AR Platform – Model SSPK556LPK, UPC 686294505645 – is a compact AR pistol build kit designed for users who want a matched upper assembly and core parts kit for the 5.56x45mm NATO platform. This kit brings together a 7.5" barrel, free-float handguard, mil-spec upper receiver, bolt carrier group, and a complete lower parts kit, providing a consistent base for AR-15 pistol builds while helping ensure compatibility across components. OpticsPlanet+1
Caliber, Barrel, and Gas System
This TacFire AR build kit is chambered in 5.56x45mm NATO, supporting a wide range of commonly available 5.56 and .223 Remington ammunition within standard pressure limits. OpticsPlanet
At the core of the kit is a 7.5" USA-made barrel with an M4 profile, designed for compact AR pistol builds where overall length and maneuverability are a priority. The barrel uses a 1:8" twist rate, which is a versatile choice for stabilizing a broad range of bullet weights commonly used in 5.56x45mm NATO, from lighter varmint loads to mid-weight general-purpose rounds. OpticsPlanet+1
Key barrel and gas system specifications include:
Caliber: 5.56x45mm NATO OpticsPlanet
Barrel length: 7.5 inches, compact pistol configuration OpticsPlanet+1
Barrel profile: M4 profile
Twist rate: 1:8" rifling OpticsPlanet
Gas system length: Pistol-length gas system for reliable cycling in short-barreled builds OpticsPlanet
Threads: 1/2x28 TPI at the muzzle, the standard thread pattern for 5.56 AR-15 platforms OpticsPlanet
Gas block journal: 0.750" diameter, compatible with commonly available .750 gas blocks OpticsPlanet
These specifications make the SSPK556LPK well-suited for compact AR pistol configurations where shorter overall length and reduced front-end weight are important.
Upper Receiver, Handguard, and Rail System
The kit includes a U.S.-made mil-spec upper receiver, providing a familiar interface for users already working with standard AR-15 components. The receiver is paired with a slim free-float 7" M-LOK handguard, offering a rigid mounting surface while helping to minimize weight. rkguns.com+1
Handguard and upper highlights:
Upper receiver: Mil-spec flat-top design, USA-made rkguns.com+1
Handguard length: 7" free-float design, sized appropriately for the 7.5" barrel
Handguard style: Slim free-float handguard with M-LOK interfaces that allows direct attachment of compatible accessories without unnecessary bulk Ammunition Depot+1
Rail system: M-LOK slots for accessory mounting (lights, grips, rail sections, etc.)
Because the handguard is free-floating, it does not contact the barrel along its length, which can contribute to more consistent barrel harmonics compared with non-free-float designs.
Bolt Carrier Group and Charging Handle
To complete the upper assembly, the TacFire AR Build Kit includes a mil-spec bolt carrier group (BCG) and mil-spec charging handle. The included BCG is designed to meet standard AR-15 specifications so it can interface predictably with compatible 5.56x45mm NATO barrel extensions and receivers. rkguns.com+1
Included operating components:
These parts are intended to provide a ready-to-install solution when paired with a compatible lower receiver and buffer system.
Buffer System and Receiver Extension Components
The SSPK556LPK kit also provides the core buffer and receiver extension parts needed for a pistol configuration. Included are: rkguns.com+2Classic Firearms+2
Pistol buffer tube (receiver extension), aluminum construction
Foam cover for the buffer tube
Heavy buffer to support the dynamics of a short-barreled, pistol-length gas system
Buffer tube spring
Standard receiver end plate
Mil-spec/commercial castle nut (steel)
These components are supplied to help users complete the rear portion of the firearm’s operating system using a consistent set of parts designed to work together in a pistol-style configuration.
Lower Parts Kit (LPK)
To support lower receiver completion, the kit includes a complete lower parts kit (LPK). This helps simplify sourcing for users who prefer a single-vendor solution for the bulk of their small parts. The LPK is specified as USA-made and is intended to provide the standard internals required to complete an AR-15 pattern lower receiver. rkguns.com+2Classic Firearms+2
Typical components in the included LPK (as listed by vendors) encompass:
Fire control group components
Magazine release components
Bolt catch and related hardware
Pivot/takedown pins and detents
Selector, springs, and associated small parts
Exact contents may vary slightly by lot; users should refer to the product packaging or vendor listing for any updated details.
Muzzle Device and Forward Controls
At the muzzle end, the barrel is threaded 1/2x28 and the kit includes a threaded flash forwarder (sometimes described as a thread device or forward-directing muzzle accessory) along with a standard A2-style flash hider referenced in some listings. OpticsPlanet+2rkguns.com+2
Additionally, the upper parts kit includes:
These parts round out the upper receiver, allowing users to configure a complete, functional upper once it has been assembled and properly installed on a compatible lower receiver.
Construction, Finish, and Overall Configuration
Most components in the TacFire SSPK556LPK kit are constructed from steel and aluminum appropriate for AR-15 pattern parts, with a black finish across the major visible components for a unified appearance. The kit is designed around the AR platform / AR-15 standard, with compatibility noted for AR-15 style builds in 5.56x45mm NATO. OpticsPlanet+1
Representative specifications from vendor listings include:
Gun platform: AR Platform / AR-15 OpticsPlanet+1
Gun type: Rifle/AR platform, configured here for pistol-length barrel builds
Hand: Right-hand configuration
Approximate weight of kit: Around 6 lb (varies slightly by source and configuration) OpticsPlanet
Color: Black
Typical Use Cases
Because of its 7.5" barrel and pistol-length gas system, this TacFire kit is aimed at AR pistol builds and compact configurations where overall size is more constrained than with a full-length carbine. Within that context, it is commonly used for:
Compact AR pistol projects
Range and recreational shooting with 5.56x45mm NATO ammunition
Users who want a matched upper, buffer, and LPK solution for a cohesive build from a single manufacturer
As with any firearm-related kit, users should follow all applicable laws and regulations regarding configuration, barrel length, and receiver classification in their jurisdiction, and should ensure that all assembly and use is performed safely and in accordance with local, state, and federal requirements.
Model, SKU, and Identification
For cataloging, inventory, or search optimization, the key identifiers for this product include:
These identifiers are used consistently across multiple retailers and are useful for ensuring the correct kit is selected when searching or comparing listings online.
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