I have put together 5 from mail order parts. There are plenty of instructions from different sites, just google AR15 assembly instructions and you'll find diagrams, youtube tutorials, and step by step guides. Do one and you'll be surprised how easy it is to do. Easiest way if you like to put stuff together is buy a barreled upper which can be ordered with a bolt carrier group and charging handle. Go with a tactical latch if you plan on scoping your rifle. The latch simply gives a longer lever to get ahold of to cycle the bolt and load(charge) your weapon. My lowers have come from Code Red and Aero Precision.
Buy a fixed or multi-position buttstock, which usually come with a buffer tube and spring, a lower receiver, and lower parts kit, and barreled upper. The standard trigger in an LPK is single stage. A two-stage kit will run you an additional $100 give or take.
With some research and a few questions, you can do this easy.
I use maybe 5 tools to assemble a lower receiver. A hammer and nail set to drive the small retaining pins into place, a screwdriver for the grip, a hunting knife to help press the detent pin and spring into place for the pivot pin, and wrench to tighten the nut on the buffer tube. A piece of cardboard from any of the parts kits comes in handy to lay under a pin you will need to tap into place. Keeps the finish from getting dinged by the hammer. I use the fine edge of a knife to hold the aforementioned pin down in its hole until I can slide the pivot pin over top of it.
Two I have now, one is a std 16" barreled flat top with a red/green dot scope, one is a free-float 20" bull-barreled gun with two-stage trigger for shooting rodents.
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