I'm looking to build me a new rifle for deer and hog hunting. I can't decide which to build. Both calibers are capable. But I have never been around an AR10 long enough to know if they are reliable and will hold up and not break on me. I currently own an ar15 in 5.56 but I will be starting my build from the ground up and will not be changing parts over if I do decide to go with the 300. If someone could help me decide and give me an unbiased view of each rifle along with the pros and cons of each from their own experiences.

There is no reason to post the same message in two or more different sections.

No need to post this four times

What is it you want to do? Because you are basically asking a question which is equivalent to "Should I get a .223 or a .22lr?"

300 sucks... I don't care what the fanboys think. Unless you are going to suppress it and use it to clear a building. You are using 556 case volume to push a 762 cal bullet, F300BLK... Anemic round is anemic.

6.5g or 6.8 are worthy for a AR15 sized package and debating with 308.

So if you are sticking with 300 as the other option then 308 all day...

I'll second this -- the only thing 300blk is the answer to is compactitude in a rifle caliber. No other common AR rifle caliber supports the use of a 7-9" barrel while retaining reasonable ballistics and projectile expansion characteristics.

I built one because the objective was to build the most compact (PDW-style) AR with the capability of defeating soft body armor or other barriers. My 300blk with 110gr Barnes black tips does just that.

As far as I'm concerned 300blk subsonic is silly -- I can shoot three rounds of .45acp for the same price and ballistics profile as one 300blk sub except my .45 HSTs are made to expand at <1000fps. Neither will defeat soft armor so all you're getting over a pistol is the increased accuracy of a shoulder fired weapon and slightly better range due to higher BC for .308 projectiles.

If you are going longer than 9" then other calibers are better -- 6.8 is good, 6.5 grendel is good, 5.56 is good. If you are going 16" or over then .308 is going to be used efficiently.

Again, it all depends on what you intend it to be able to do. I built to fit a specific profile as stated above -- what's your objective?

I didn't post it 4 times, I posted it once..here in this section

They work pretty darn good on deer when you are in the woods and your average shot is 150 yards of less, my wife and I have put 4 deer in the freezer with the .300 black over the last two seasons and all 4 of them were 1 shot kills.

If you are not wanting to reload, then I would say it is an expensive gun to shoot, but I reload and have built the loads for both of our rifles and they are quite reasonable now.

If I need to go further I grab one of my .270 or .308 bolt guns, which I use for elk and Pronghorn.  If you know the guns limitations and use it correctly it is fine and it works well for deer sized game.

Neither.  Grendel.

Except that niche that was mentioned above...the other 3 do everything better than 300blk... Someone at LaRue took an elk at 400 yards with grendel, don't think you are gonnna want to try that with the blk.

I would never dream or attempt to take an elk at 400 yards with a black, the round was not designed to do that kind of shooting.  But for a woods situation like I have were I live, it is short, light and has the ability to drop deer sized game with no problem at all.

If I am hunting bigger game I use more powerful guns.  Just not in the AR style gun.

I'm a hunter myself and own 308,300 and 6.5 Grendel,I would choose the Grendel.

My exact thoughts.

To say its sucks is just being ignorant. And looking through the 6.8 and 6.5 threads you can see why they are ignorant.

I use the ar platform for fast follow up shots to shoot multiple deer because the 300blk has almost zero recoil. When i was considering an AR for hunting I looked at the grendal, spc, wolverine and blackout and found the blackout is all i need shooting deer minus 100yds  in the woods.

The ar10 is to heavy for me to lug around the woods when i can grag a sub 7lb rifle and do the same thing.

I agree that 5.56 is better than 300BLK in most ways but in localities where it is not deer legal, and the question is 300BLK vs 308, 308 is a better caliber but a 308 AR isn't necessarily the better platform. Parts, mags and guns are more expensive and harder to find. Guns are heavier and larger. Inside of 400 yards, supersonic 300BLK can be very effective.

I have rifles in all of the above calibers. I would rather hunt with the lighter 300BLK but I don't hunt at long ranges and I do a lot of walking.

He's right, Grendel is the best choice.

My next build will be a 6.5 CM.

Grendel or 308.  The 300 is ok out to 250. It's capable of making hits further but I haven't been impressed with the results on deer. I've taken 3 between 100-200 and 1 at 307 and the blood trails are sketchy to non existent the closer you get to 200.

Since you're building a "hunting" rifle there's alot of options for making it as handy as you want.

The 18" PA10 I've been playing with feels closer to a 15 with the lightweight scope and mounts than the AP4 I've been dragging deer hunting for 10 years.

Well as we all know, opinions are like........

And we all have one.

Not designed to shoot deer at 300, also bullet choice makes a lot of difference, anybody trying to take a deer at 300 with a black is simply not an ethical hunter and is playing stupid.

If I am anticipating over 150, I take either my .308 or .270 bolt guns..

Won't argue that.  This was early in the Black hype where it was the greatest cartridge ever conceived for the AR15, Haley was posting videos hitting steel at 900 yrds with a 10" pistol, barnes had nuclear bullets and people would say things like 500yrd deer cartridge.  It was the last day of season, the freezer was empty, and conditions were perfect.  Aimed for the high spine and dumped her right there.  Pulled the hide and couldn't find blood or a hole.

You don't know what you don't know and Hype is a hell of a drug.