I am looking to build a 6.5 Grendel using mega arms upper lower combo, blackhole weaponry 18" mid length barrel, with cmmg piston kit. I just want to see what your thoughts are.
Welcome to the board.
Well as to my thoughts, I would say the BHW barrel will perform well for you. Groups on my 264 were excellent and many shooters have been extremely pleased. If this is your first BHW tube you are in for a treat the first time you try to clean it. You will think all your solvents went bad as the coper fouling is non-existent and it only takes minimal effort to get them squeaky clean.
The best firearm for self defense? Any loaded one will do.
I built my Grendel with a 16" BHW bull barrel. Rounds 47-50 through the barrel netted a .686" group with Hornady AMAX Match ammo. There is definitely potential for sub-.5" groups. You won't be disappointed.