Thinking about an additional upper, for deer out to 200. 6.8 seems to be the best compromise of off-the-shelf ammo vs ballistic capability, although with .300 you have the subs possibility. 6.5 is obviously the most powerful but has limited ammo options, and I can always pull out the bolt actions in 7mm-08 or .308 at that point. What say ye?

I am partial to the 300 blk. I haven't shot the other rounds so I cannot offer a comparison.
One thing I like about it is the use of standard AR mags. There is a wide range of projectile possibilities from 110 to over 200 grains.

Mine has taken many pigs and a couple of coyotes.

Big fan of the 6.8 caliber and believe it is the best hunting caliber on the AR platform. The 6.8 is neck and neck with the Grendal until about 300 yards, at that point the grendal has the edge. That being said the 6.8 has a wider range of bullet options and ammo availability. Next is the 300BO, all I will say is I have friends and customers that bought into the 300 hype for hogs and shortly after that sold them for a 6.8. I personally don't own a 300BO so only speaking from my experiences with other people. I have killed hundreds of pigs with the 6.8 and if you search other forums about hog hunting the 6.8 is the highest percentage caliber used.

If you ain't runnin a can I see no use for the 300BO. 6.8 all the way!

Simple reason I love the .300 Blackout. Hits pretty damn hard with Barnes Vor-TX 110gr at ranges less than 150yds and recoils like a .223/5.56. Also my AAC MPW is pretty damn accurate.

Most of my shots are within that range and my 8yr old son can use it with ease. Win, win.

I am in the same debate... I have a 300 BO that i will use for hogs inside 100 yards.

I wanted an extra upper for deer rifle back up. The 6.5 has the better bullets but the 6.8 has the better availability. If the 6.8 had the AMAX bullet i would be game. But all there is is hunting bullets.

If you want to shoot quiet and have a can, then I'd say go 300blk. Especially go that route if you are going with a short SBR. My SBR 300blk with a can attached is shorter than a 16" rifle.
If you don't have a can, then the 6.8 is a sweet shooting low recoil round.
I've never shot the 6.5G.

I've never had a problem shooting deer or pigs with the 300blk. Out to 200 yards, any of the rifles will work fine. So I would look at availability of the upper/barrel you want and cost/availability of ammo.

Info I got from Barnes and Hornady that compares the 2 calibers. The ammunition used is the Barnes 300BO 110r TAC-TX and in the 6.8 it's the Hornady 120gr SST. Both rounds seem to be the go to ammo for both calibers, offering some of the best performing for each caliber.

300BO______Muzzle____100 yards____200 yards____300 yards____400 yards
Trajectory____-1.5_________0__________-6.7_________-24__________-55.5
Velocity______2350_______2070_______1810________1574__________1369
Energy_______1349_______1046________800_________606__________458

6.8_________Muzzle____100 yards____200 yards____300 yards____400 yards
Trajectory____-2.40________2.2__________0__________10.5_________31.1
Velocity______2460_______2250________2050_________1862________1685
Energy_______1612_______1349________1120_________923__________756

As you can see the 6.8 has less drop than the 300 BO. At 100 yards it has 8% more velocity and 200 yards it has roughly 12% more. At 100 yards the 6.8 has 22% more energy and at 200 yards it becomes roughly 28% more than the 300BO. Pretty cut and dry!!

This data came from the ammo manufactures website.

24 inch barrel. 6.5 Grendel 123gr SST From Hornady website , A-max also available
Velocity (fps) / Energy (ft-lbs)
MUZZLE____________100__________ 200____________ 300____________ 400_____________500
-2.40__________ 1.80___________ 0.00___________ -8.70__________ -25.30_________ -51.30
2580/1818______ 2410/1586______ 2247/1379______ 2090/1193______ 1940/1028______ 1796/881

Rifle (16" Barrel) Velocity (fps) / Energy (ft-lbs)
MUZZLE_________ 100____________ 200____________ 300____________ 400____________ 500
2350/1508______ 2189/1308______ 2034/1129______ 1885/971_______ 1744/831_______ 1612/709

Apples and oranges. Why aren't you comparing a 110g 300blk bullet to a 110g 6.8 bullet? It's a bigger lighter bullet, of course it's going to be much different. Velocity difference means squat at those speeds and 200 yards. As long as it's enough to expand the bullet with good penetration, what does it matter? A 4.5" difference in drop at 200 yards... not going to matter if you are practiced with your rifle and know the drop. And look at the Trajectory of the 6.8. How does a bullet go from hitting 2.4" high at the barrel, to 2.2" low, to zero, and then to 10.5" low? Isn't that a big 'W' flight pattern? Something isn't right there.
Anyway, if you base all your purchases on numbers on a piece of paper, then you should only be hunting with a 50 BMG because its numbers blow away most other rifles. Pretty cut and dry.

Your numbers came from a 24" barrel, not a 16" like the others. So lets compare apples to apples
MUZZLE____________100__________ 200____________ 300____________ 400
2350/1508______ 2189/1308______ 2034/1129______ 1885/971______ 1744/831

That makes the 6.8 outperform the Grendal to about 200 yards. After 200 yards the Grendal slowly pulls away

I was just putting information out therefor the OP. Energy on target is energy on target!!! I used those 2 bullets because they are supposed to be one on the most effective. Here is a 110 gr Hornady V-max and it still has more energy on target than the 300BO!!

6.8 110 gr Hornady V-max
Barrel (16") Velocity (fps) / Energy (ft-lbs)
MUZZLE -------------100 ----------200 ---------300 ------400
2550/1588---------2319/1313-------2100/1077------1893/875----1700/706

I have a 6.8 and 300 BLK. The 6.8 is a little better as 200 yds is close to max for the 300B. But when in doubt get both! The 300B is a beast at close range!

Considering 200 ft/lb of energy will kill a deer or pig, the difference in energy between all 3 rounds in 200 yards is pointless.

i prefer grapenuts

I have the blackout and the 6.8 the blackout stays in the safe now. Compared to the 6.8 the blackout was underperforming on hogs, I don't know about all the numbers just real word experience. Will a blackout kill hogs yes it is the ballistic equivalent of a 30/30. The 6.5 is nice also but I feel the 6.8 will be more commercially available.

So between the three my choices would be 1) 6.8. 2) 6.5 3) 300bo. They will all kill hogs with proper shot placement some provide more room for error than others. Only reason I can see to chose the BO is cost.

It's actually pretty simple. 300 black if you're going to do an sbr and suppress it for short range hunting. If not that scenario then grendel and 6.8. 300 is a very specific gun. For me it is perfect though for my hunting scenario which is night vision and suppressed at less than a hundred yards at night. In distances further than that the 300 sucks. I have two of them and love them but for what you're wanting I think you'll happier with the 6.8. The 300 will bring down huge hogs but shot placement is key just as it is with any other round on a big tough plated hog.

MDMorrow, I agree with you on the 300 BO working well out of SBR's and short distances but the 6.8 performs well out of a SBR also. Where as the 300 BO is good down to +/- 8" the 6.8 does really well at 12.5" and up.

Get a 6.8 and a 300BO. You can never have too many choices! Oh, and a 458 socom too!

Stop muddying the waters with scientific data!

Ballistic coefficient paired with muzzle velocity, yeilding more retained velocity and energy is not welcome here!

I should have clarified. 8.2" noveskes are what I run for a couple reasons. The shorter and lighter the better as most of my hunting involves thermal spotting then stalk up to take the shot. We have a lot of cows so getting up closer for positive ID is a necessity as is a lightweight rifle since a lot of walking is involved. If I was shooting for a longer distance I'd be using something in a large bore AR platform. I had a JP but found I never used it since my chances of a nighttime distance shot on our place is rare.

Muddying with scientific data?? Lmao. Its performance info off the manufactures website. OP asked a question so I put information out there so they would have info available to choose. No charts or graphs from a program or coefficients. Posted the stuff I looked at when I was deciding on a larger caliber for hunting hogs. If it bothers some folks, don't read it.

Sarcasm detector must be broken.

Well, I have 2 300 Blackouts, 1 10"SBR, and 1 16". I also have a 20" Grendel, and a .50 Beowulf. I don't own a 6.8, and I don't plan on owning one.
But I don't like .270s. (.277) or (6.8) but that is my choice! But I like .264 bullets, and .308 bullets.
But, that's why they make so many calibers.