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I think the AR name on the lower is like the chevy,ford, dodge thing
Lowers are pretty much the same except for the post ban Colts, they use a larger fire control group pin set and the front take down pin is an oddball thing. Choosing any forged aluminum lower of your choice and the only difference is surface appearence and the brand name roll marked on the side. There are some lowers that are machined from billet aluminum but they tend to be expensive and often times heavier than forged aluminum but they are very nicely done.Upper recvr's are again pretty much the same, mostly all forged aluminum and for the most part Mil-Spec. There are some different grade bolts and a few minor cosmetic differences in bolt carriers but they all function the same. The true heart of the AR is the barrel and good quality trigger, which there are several out there to choose from in both single and two stage.If you are looking to build a blaster/plinker then any lower parts kit with standard trigger will do. If you are looking at a true custom gun take a look at JP Enterprises.