File:Mitch Barrie - flickr - AR-15 stripped lower receivers.jpg

English: A collection of AR-15 stripped lower receivers, the starting point for any AR-15 rifle project.

I have a nasty habit of buying a couple of stripped lowers every time I pick up a gun at a gun store (they have to be registered upon purchase like almost all other firearms here in California, NICS check, ten-day wait, the whole nine yards; don't you feel safer?). After a short time the lowers start to pile up! But I guess you can't have too many stripped lowers.

The two in the front are of historical interest. On the right is a Fab-10 with a sealed magwell. For several years after 2000 these were the only magazine-fed AR-15 lowers legally available in California. You had to remove the takedown pin and open the receiver to load the rifle. If there was a jam that prevented the bolt from going fully into battery, you were screwed (well, you had to remove the pivot pin to clear the jam). That's the main reason I never actually did anything with this lower.

On the left is something even weirder: a DPMS single shot AR-15 lower. I bought it when I started my business because I needed an AR-15 lower and aside from the Fab-10 this was all I could get. There is almost no use for such a lower, though they were often employed to build .50 BMG rifles such as the Ferret50. I nearly bought one of those before they, too, were banned in California.