The AR-15 is an excellent weapon there are so many vendors out there selling their version of them that the improvements have been astonishing. I have a Colt that was mad in 1978 and it’s OK as far as it goes. I have built better weapons from parts obtained from various manufacturers beginning with the lower receiver at a total cost of around $500.
Start here....if you dare.
https://www.vbd.com//noc/shop/products_detail.asp?CategoryID=29&ProductID=122
Later reference...