Welcome, let me muddy the waters even more, by saying that Armalite makes the best lpk's, which can be cross platformed, so buy one for your build! I personally think that Geiselle has the best triggers. Your buffer tube can be an ar15 part, I suggest mil-spec, and the best buffers and springs on the market belong to Clint at Heavy Buffers. Barrels, I like the Rainiers Ultramatch, DPMS based, so stay with that pattern for your bcg, which imho the best are made by Young Manufacturing. GOOD LUCK , HAVE FUN!