SI Defense Billet
AR Lower Receivers

SI Defense’ AR-style lower receivers are refined and strengthened in key areas to perform flawlessly and to have great aesthetics. Made from 100% billet aluminum guarantees a true dimensions and great looking lower that will be reliable for years of service.

Si Defense billet lower AR-15 receiverStandard Build Specifications for the AR-15 and AR-308

  • Fully machined from solid billet aluminum.
  • Optional forged AR-15 .223/5.56 lower receiver
  • Receivers marked "Multi-cal"
  • Material: 7075 aluminum.
  • Coating: Black anodized to MIL-F-8625F and AMS 2471F.
  • Optional FailZero coating on lower receiver
  • Optional anodize colors: Flat Dark Earth, O.D. Green, Clear, and Desert Tan
SI defense billet lower failzero

7.62/.308 Lower Receivers

Because the are many different hardware manufacturers and suppliers of the 7.62/.308 receivers, SI Defense produces two different versions of the lowers and two versions of the uppers. These lowers are specifically manufactured to match each respective model. These models are not cross-compatible. These lowers will accept DPMS® lower parts kits.

  • SI AR-D: Lowers will fit DPMS® magazines and uppers, Magpul® Pmags
  • SI AR-HK: Lowers will fit HK91/G3® magazines

Please note that because there are so many different manufacturers of receivers and components, SI Defense cannot guarantee fit and finish with their components. If you have question in regards to fit, function and finish, please email or call us.

SI Defense billet 308 caliber lower receiver
SI Defense billet 308 caliber lower receiver

SI Defense HKG3 lower receiver is now shipping

SI Defense HKG3 lower receiver is now shipping