Quality, mil-spec AR-15 Rifle and Pistol lower build kits.
What good’s that shiny new upper you bought for your AR build, if it doesn’t have a quality lower build kit to finish off the other half? Instead of guessing which parts to grab – the lower parts kit, the right buffer, a good pistol grip, and everything else – just grab it all n’ go with one click. Our lower build kit options include all parts required to outfit a barreled upper assembly, turning it into a ready-to-roll AR rifle or pistol build.
What’s in a Lower Build Kit?
Just about everything you need (minus some basic gunsmithing tools, like a castle nut wrench and roll pin punches) to build out the bottom half of your AR’s two assemblies. A lower build kit includes the following components, which are all you need to make an upper receiver function with a magazine, trigger, and buttstock and/or buffer tube (if building a pistol):
- Lower Parts Kit (fire controls, pins, and springs)
- Standard pistol grip with screw and crush washer
- Mil-spec Carbine buffer tube (works with rifles and pistols)
- Mil-spec buffer and recoil spring (buffer weight depends on caliber)
- Forged or billet 80% lower receiver (requires an 80% jig to fabricate)
Lower parts kit install instructions available.
A: What does “mil-spec” mean?
A: That means the parts included in your Lower Build Kit are fabricated to a universal standard of fitment for the AR platform. Over 95% of AR parts on the market (including receivers, buffers, and buffer tubes) are “mil-spec” in their fit and finish. The mil-spec identifiers here mean your buffer is made to fit in the most commonly sized buffer tube (diameter of 1.148″) which is also included with each kit. These mil-spec tubes and parts fit virtually all upper and lower receivers, including all our 80% lowers. Here’s a more detailed guide covering it all.
Q: What else do I need to build an AR?
A: The lower build kits you see here allow you to complete an entire lower receiver assembly. Once you have a lower assembly with a functional receiver and trigger installed, you only need a barreled upper assembly with a bolt carrier group and charging handle. To make things even easier, we have complete build kits that include what you see here, plus an upper assembly. Want to build a custom AR piece by piece? Check out all our available AR parts. We have bolt carriers, handguards, stripped upper receivers, custom charging handles, and more.
Available in 5.56/.223, 9mm, .308 and more
No matter what type of upper assembly and caliber you chose to chamber, we have compatible lower build kits. The Classic Kit is perfect for completing a mil-spec 5.56 NATO, .223 Remington, 300 Blackout, or even a 6.5 Grendel build. All parts contained in this kit work with all those uppers and calibers!
Building a .308 AR? Grab this Lower Build Kit, which includes a billet .308 80% lower. And finally, for those building a 9mm AR (AR9), we’ve got you covered with this 9mm Lower Build Kit. It includes the appropriate buffer assembly and a 9mm 80% lower with the correct ejector.