A list of the internal parts for the AR-15 lower receiver.  Please note: AR-15 lower receiver parts and M-16 parts are different, and,  As of May of 1986 there can be no new machine guns made for the civilian population.

AR-15 lower receiver parts are as follows:

Buttstock Buffer Spring (Std)  Buttstock Buffer Spring (Car)  Buffer Assembly (Std)  Buffer Assembly (Car)
Selector  Selector, Bolt Catch Spring, Bolt Catch Detent  Bolt Catch  Bolt Catch Roll Pin  Magazine Catch, Magazine Catch Assembly, Detent Spring, Takedown Detent,  Magazine Catch Spring  Magazine Catch Button Aluminum  Magazine Catch Button Al Radiused, Front Pivot Pin  Disconnector  Colt Large hole Disconnector Disconnector, Pistol Grip Screw, Pistol Grip Lock Washer  A-2 Pistol Grip, Black Plastic
Selector Spring  Detent (Selector)  Trigger Pin  Hammer Pin  Large hole hammer/trigger pin  Rear  takedown Pin  Buttstock Aluminum Spacer.