All of Blackheart International's three lower receiver platforms—the BHI SPR, BHI SSA and BHI MIL-SPEC—were developed around the purpose-built BHI-15 lower receiver. This precision-engineered semi-auto lower receiver is CNC-machined from solid aluminum billet for maximum strength (compared to casting), and to eliminate dimensional inconsistencies (compared to forging). Additional features include an oversized magazine well lip for easy magazine insertion, receiver extension tube reinforcement, and a hardened black anodized finish for durability. The multi-caliber design allows this receiver to be used to custom-build your rifle in a variety of calibers.

Blackheart International's lower receiver assemblies provide a solid foundation for any AR-style custom rifle package, allowing the builder to gear up with their choice of upper receiver assembly and barrel configurations, or select from one of Blackheart International's four pre-configured 5.56 NATO upper receiver/barrel assemblies. All BHI-15 upper receiver assemblies feature 16- or 20-inch precision medium-contour Criterion barrels, the exclusive BHI-15 Rifle-Length Hand Guard system, and the choice of a forged aluminum A3 flat top or billet aluminum Slick-Side receiver. Also available is the BHI-15 MIL-SPEC upper receiver, with its 16-inch medium-contour Criterion barrel and A3 flat top receiver.

• BHI SPR

This model is fitted with a premium Stark pistol grip, Wolff Springs for reliability and improved spring energy over stock or replacement-type service springs, plus Geiselle's DMR (Designated Marksman Rifle) trigger group. The DMR trigger is a two-stage adjustable unit, making this an ideal trigger for everything from precision tactical/target shooting to hunting. Backing the assembly is the Magpul PRS (Precision Rifle/Sniper) stock, which features fine-tune cheek riser height and length-of-pull adjustments combined with a machined aluminum butt-plate and alloy steel adjustment shaft for maximum strength and shooter comfort.

• BHI SSA

It delivers the same BHI-15 lower receiver, Wolff Springs and Stark pistol grip, but incorporates the field-proven Vltor Clubfoot six-position collapsible stock and Geissele SSA (Super Semi-Auto) two-stage trigger. Among the benefits of the Vltor Clubfoot stock are the modular Cheek Weld Adapters for a custom fit, easy adjust lock system, quick-detach sling swivel adaptability and the "Clubfoot" design itself, which allows the shooter to support the base of the stock with the non-firing hand.

• BHI MIL-SPEC 

The BHI MIL-SPEC includes the same BHI-15 billet lower receiver and Wolff Springs upgrade as the aforementioned lower receiver assemblies, but is outfitted with a MIL-SPEC trigger group, A2 pistol grip and standard 6-position collapsible stock.