Selectorhole Rearpivot-pinhole Frontpivot-pinhole Triggerpinhole Triggerslot Hammerpinhole Selectorretainerhole Magazine well Trigger guard holes Pistol grip area Buttstock$60 Lower receiver assembly $120 Trigger kit (includes pistol grip) $70 LOWER RECEIVER FINISHING THE FINAL COST OF A SERIAL-NUMBER-FREE AR-15 Magazine$12 Upper receiver assembly, barrelassembly, bolt carrier andcharging handle $700 The customer can order an 80 percent complete, serial-number-free receiver from most manufacturers. All that remains is for the customer to drill trigger, hammer and selector holes, and cut the trigger slot. Manufacturers then sell a kit of 30 internal trigger parts required to turn a lower receiver into a fully functional unit, ready for assembly to the upper receiver, charging handle, bolt carrier, buttstock and cartridges.

SOURCE: bravoccompanyusa.com, colfaxtactical.com, impactguns.com. GRAPHIC: Alberto Cuadra and Richard Johnson - The Washington Post.