Andro Corp Industries ACI-15 Partial M4 AR-15 Lower Receiver

A partial lower gets you past the fiddly stage of an AR-15 build without locking you into somebody else's parts list. Andro Corp builds the ACI-15 on an aluminum M4 pattern receiver marked multi caliber, so the same lower is legal ground for a 5.56 upper this year and something else next year. It arrives with the core components in place. What you add is the stock and the upper, which are the two decisions most builders actually care about.

The receiver is cut to standard M4 dimensions and finished in black, so a mil spec upper mates up with no fitting work. Everything left is hand tool territory. Choose an upper, put a stock on the back and the rifle is done. For a first build this is a sensible middle ground, less bench work than a stripped receiver and none of the compromises that come with a complete rifle somebody else specified.