So this isn't a thread looking for a seller, just asking a few questions. I'm looking into buying an AR-15 rifle and i have found its much more difficult to research this properly than a handgun, which i spent a few weeks doing. I'm confused on the part that many second hand lower receivers cost more than new and the fact that everyone says specific ones are better for quality. Now the part that i get is that, sure some can be better than others purely looking at the materials used in production. Also some of the older ones may be considered more reliable(or maybe more trusted) but does that mean that i wont be able to get any stripped lower receiver for less than $400 anymore? next is, how do i know that when i buy parts separately to build the rifle over time that they will meet the minimum legal lengths? will i have to account for the threading when i put them together (19" barrel will be 19" plus the threads and same deal with the stock?) or will it be the 19" includes the length of the threads also? aside from how to tell which calibers they will accept including multi-caliber lower receivers i also can't seem to find which questions i should ask when looking at purchasing a specific rifle from a person or dealer when i feel i am ready to purchase. At this point i have decided these things: -I want to get at least a lower receiver before any new laws prohibits, restricts or otherwise makes it much more difficult to acquire one (pretty obvious but not necessarily pressing i suppose) -the lower receiver should be .223 or multi-caliber able to accept .223 (mostly because it is the most common choice and has the highest supply of parts, options and ammunition. i also have experience with this and enjoy it) -cannot be exclusive for options available (such as the old colts, which only accept the old colt uppers) can anyone help me with this, so that i don't make a terrible choice when i later purchase my rifle?