You ever had a brain fart?

I asked this earlier today but thought i'd post it again to see if anyone else had any thoughts. First things first though,last night while under the influence of too much alcohol I answered a question and said the an M14 fired 30.06 Springfield. Duh! I know better but like I said I had a brain fart. My apologies to you all, especially the asker. Now I have a question for you fine folks. I want another upper for my AR. I was thinking of either a 6.5 Grendel,6.8 Rem or a 300 Blackout. This will be a hog buster gun. I want something that can reach out quite a ways. Here in Texas some shots can be fairly long range. I'm leaning toward the 300 for the reason of being able to form cases from .223/5.56 brass(brass availability is a biggie,although it was pointed out to me earlier that the Blackout isn't a good long range round). So if any of you that have fired any of these cartridges could give me your opinions i'd appreciate it. I'd like opinions on the best barrel length from those of you with experience using any of those calibers( I was thinking of going with a 24" barrel). Also if any of you have hand loaded any of these are there any things to be concerned about? Such as short case life,finicky about powder types,etc. Thanks in advance.