Parchaser, thanks for showing that info. I have all 3 cartriges you mentioned: 5.56, 300BLK, and 7.62x39. Here's my take:
Its not surprising that 300Blackout and 7.62x39 have similar ballistics, although the 300BLK shot lower given the smaller case capacity. When you said you were thinking of going 9" on the 300Blackout for hogs, were you talking about a SBR/Pistol setup?
300Blackout is optimal for short ranges and with suppressor use. Depending on your range, under 150yards you should be ok but a 9-inch barrel would obviously be a bit different due to the shorter length. If you already have 5.56/223 and 6.8, the 300BLK is a good round to go with. Just understand its purpose and limitations. The 5.56 and 6.8 will be better for longer engagements, but for anything under 150yards the 300BLK should be a good round.
So in short, if you wanted to use the 300BLK for hogs it would be better to stick with a 16" barrel so you get better performance out of it. Remember that 300Blackout is designed really both for suppressed/unsuppressed use out of the same AR15 parts save the barrel. Its also more suited for CQB type situations, so knowing that, make your decision.
You already have 5.56 and 6.8 so those would probably be better for hunting at farther distances over 200yards.
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Samuelcmm, depending on what type of 3-gun you plan to do, either 6.8 or 300BLK should be ok although the 6.8 will have the advantage if you have long distance rifle stages over 200yards. Anything less than that and the 300BLK should work well.
Do you already have a 5.56/223 AR? If not I would highly suggest the 300Blackout for the purposes of better interchangeability with AR15 parts. If you already have a 5.56/223 then obviously 6.8 might be better, but only slightly.
I personally love my 300Blackout AR
. But for all-around multi-purpose use, you can't beat the ol' 5.56/223