Andro Corp Industries ACI-15 Multi Caliber AR-15 Lower Receiver

The ACI-15 is Andro Corp Industries' AR-15 lower receiver: aluminum, black anodized, and carrying a multi caliber designation, so the same housing serves whatever chambering the rest of the build is put together for. Chambering lives in the barrel and the upper, not down here, which is why one lower routinely outlasts three or four different uppers on the same shelf.

This is the serialized piece and the part everything else hangs off of. It takes the fire control group, the selector, the magazine catch, the bolt catch, and the buffer tube, and it sets the geometry that the upper closes against. Anodized aluminum is the standard recipe for a good reason: it is light, it shrugs off solvent and sweat, and it wears in rather than wearing out. Andro Corp keeps the ACI-15 to the common AR-15 pattern, so the lower parts kits, grips, triggers, and stocks already sitting in your parts bin are the same ones that go on this receiver. If a build is starting from nothing, this is the piece it starts with.