By now you've caught on to the fact that using an 80% lower receiver to build your new AR-15 or other rifle or pistol is probably the best approach: You're skipping the background check and NICS fees, the transfer fees and special taxes, and you're avoiding the branded premium prices. But how do you actually complete your 80% lower? We're covering the four ways you can cut and drill your receiver to make your homemade AR-15 stripped lower:
Either Way, You'll Need a Jig
Unless you have access to a commercial-grade CNC machine with precise CAD drawings and measurements of an AR-15 receiver, you'll need to stick with using an 80% jig. Jigs are typically categorized by the tools you have at your disposal to complete your lower: A drill press or mill, or handheld router. let's review all three.
Option 1: Use a Drill Press
A drill press provides a stable, fixed machining platform for completing your 80% lower receiver. Using the drill press in tandem with a center-cut end mill bit (which is included with the 80% jig you'll purchase for your lower), you can complete the bulk of the fire control cavity using the provided drill bits and pilot hole template, followed by making vertical plunge cuts with the end mill to smooth out the floor of the receiver. Very light milling passes can be made with the appropriate chuck on your press in order to smooth out the aluminum face on the interior walls of the receiver, too.
- Using a drill press is easy: You simply set the required depth you need to drill to, and plunge the bit into the receiver as the jig guides you. Complete the necessary pilot holes and complete the rest of the cavity with the end mill bit.
- A drill press is stable: If you're not experienced with machining metal or working with power tools, a drill press is an easy machine to master. It's stable and easy to control, allowing you to work slowly as you build confidence.
- It's affordable, too: Compared to a router or mill, a drill press is an affordable and versatile machine. A decent press can be had under $250 that provides plenty of torque and precision for basic work like this.
- Using a press is the slowest choice: Mills and routers can cut the bulk of the receiver's main cavity laterally. That is, making side-to-side cutting passes to shave down the aluminum in the receiver, which is quicker than performing the bulk of the work using drill bits and plunge cuts.
Option 2: Use a Mini-Mill
A mini-mill, like the Sieg X2 shown above, is unarguably the best way to complete an 80% lower receiver: It combines the stability and control of a drill press -- in truth, much more control -- with more cutting power than a handheld router. With precise depth and lateral adjustments, the mini-mill can effectively cut the fire control cavity in your lower in short order, providing clean results with only a single pilot hole drilled as a starting position.
- A mill is the most effective and fastest: It provides the highest level of cutting precision and power required for machining a firearm receiver like the AR-15's lower. Using a mill, one can complete a receiver in 15 minutes.
- It's the safest choice, too: A mill is an incredibly heavy and stable machining platform, with a tool chuck design to accept high amounts of lateral force without risking damaging the machine or the bit itself.
- It's the most accurate: The mill's adjustment knobs for vertical and lateral movements are often as precise as 0.0001", allowing for incredibly clean cuts without damaging your 80% jig or wearing our your bits.
- A mill is the most expensive choice: The most affordable mini-mill, like the Sieg X2, will cost between $550 and $750, with more expensive units approaching $1,000 to $1,500.
Option 3: Use a Router
The router is the main competitor to the drill press and milling routes. Rather than using a fixed platform and moving the jig and receiver to cut the main cavity, the router requires the jig and lower to be secured in a vise, while the router moves laterally, cutting the cavity. This is provides similar results to a milling machine, albeit with less precision and stability.
- Quicker than a drill press: Using a drill press will take approximately 1 to 2 hours' time to complete your receiver, while a router can get the job done in approximately 30 minutes to 1 hour.
- Less expensive than a mill: A router is more affordable than a fixed milling machine, with costs comparable to that of a drill press.
- Provides clean cuts: Although not as precise as a mill or drill press, the router, when used in tandem with the appropriate jig, provides clean cuts and a smooth finish with relative ease.
- May be less safe: Since the router is handheld, it is up to you, the builder, to ensure the tooling remains stable and doesn't cause damage to the router, bits, or worse, yourself.
- Obscures the work area. The router's adapter plate will obscure the work area while you cut the receiver, so you must ensure your measurements are correct, and you must rely on the jig to ensure the router only cuts where it is supposed to.
- May be redundant: Even though you'll use a router to cut your receiver, you still need a drill press to properly drill the pin holes into the walls of the receiver for your parts kit. This could be considered a redundant method of machining, since you can complete the entire receiver with only a drill press.
- A drill press is the most affordable method for completing an 80% lower.
- A milling machine is the most effective and precise method for both cutting and drilling.
- A router is an affordable alternative to a milling machine, but you'll need a drill press anyway.