Man, you guys are harsh. Why all the 300blk hate here? I just built a 16" carbine, and I love it. I'm in Illinois - we're not allowed to have anything fun at all. No SBR's, no cans, no rock 'n' roll switch...and I still love it. Since everyone here has gone all negative nancy and pointed out the cons, here's a few pros:
Only difference between .300blk and a 5.56 rifle is the barrel, which means you can use the same mags you already have. That alone can save you some $$. If you don't want a dedicated 300blk rifle, you can also just build an upper and pop it on your favorite hunting lower. Its also worth a mention that the ballistics and trajectory are NOT as bad as some would have you think. If you use a 125 or 150 yard zero, the holdover is totally manageable. I think the only ones who are afraid of a little bullet drop are the ones who don't know how to range a target, but I digress.
I do think 300blk is a great option for deer, at least until deer start wearing some kinda body armor.
Anyway, FWIW, mine shoots really well with 125 grain Speer TNT's and Nosler Ballistic Tips.