The Instagram tag #ar15 has over 1.7 million posts, with updates by the minute  By Jon Schuppe (Repost credit NBCnews.com)UPPER MARLBORO, Md. — There are a lot of reasons people love their AR-15 semiautomatic rifles, and it doesn't much matter to them what the haters say.For some, the gun is a tool, a finely tuned machine that can cut down an animal or intruder, or pierce a distant target, with a single precise shot.For others, it is a toy, a sleek beast of black plastic and metal that de …

DECIDING WHICH AR-15 TO BUILDBefore you buy your first part, decide what kind of rifle you want. Will you be varmint hunting, plinking or competition shooting? Once you make this decision, you know what type of upper receiver and barrel you will use. The upper receiver and barrel you choose will determine the remaining parts needed.Here are several types of stripped upper receivers, each with different features for different applications.AR-15 A1Has a fixed carry handle, shell deflector and requ …