I absolutely have too many AR-15's, that said one of my favorite's I shoot nothing but 40gr BT's out of it. I tinkered with many different powders and in my rifle the best powder was Benchmark, start at 25.5grains and work up from there. If you cant find Benchmark VVN133 came a close second.
What utah708 calls a Tunable gas port the AR-15 snobs call an AGB (adjustable gas block). one of these is not really necessary but you can fine tune your rifle with one if you wish
