Barrel length

[Tbugg90]

I am building a 308 AR for hunting deer sized game out to 250 yards and possibly target shooting out to 500 yards. I am trying to decide between a ballistic advantage 16 inch and 18 inch barre. Any recommendations?

[DNP]

16 will do all that just fine for you. 

[shooterrex]

My 16" does good farther than that.

My 6.5 Creedmoor is 16" too and I know it does 850 yds.

[Armed Eye Doc]

If you carry the rifle around while hunting, that extra 2 inches of weight is not needed for your intended use.

[98Z5V]

My opinion, which doesn't really matter.  I think 18" barrels are the perfect length.  It's the very best mix of precision capability, and maneuverability.  It's easy to make a gun with an 18" barrel do whatever you need to do, in almost any situation or circumstance.  To me, anything with an 18" barrel is the perfect AR gun, perfect precision gun.  You don't need any more barrel than that, for whatever that cartridge you're shooting is capable of.  If you can't make it perform, with an 18" barrel, you're not gonna get it to perform with a barrel that's longer, either.

Now, I'm going to contradict everything I just stated, based on your conditions, desired goal, and shooting description.

Do the 16" BA barrel.  BA makes fantastic barrels, sub-MOA guarantee if you're using match ammo, and I can confirm that every barrel I've ever purchased from BA is certainly a sub-MOA barrel.  More expensive barrels aren't gonna give you a huge leg-up over a BA barrel. 

4 hours ago, Tbugg90 said:

I am building a 308 AR for hunting deer sized game out to 250 yards and possibly target shooting out to 500 yards. I am trying to decide between a ballistic advantage 16 inch and 18 inch barre. Any recommendations?

^^^ Based on that end statement that you started out with - excellent, by the way - the 18" barrel isn't going to give you an advantage over the 16" barrel, based on your desires for the gun.  It just won't.  It's simply more weight on the gun, and more importantly, swing weight of a longer barrel.  Swing weight is a big deal, moreso than carry weight. 

I've run my 16" BA barrel out to 1k yards, when I feel like setting those targets up, but more routinely out to 850 yards, which I set up often.  The 16" is more than capable for that distance, and it does it effortlessly.  1k is a different story for a 16", but it's possible, and repeatable, once you have the wind calls figured out that day. 

My vote, for your case - 16" BA Barrel.  For what you want the gun to do for you, the 16" will easily handle that, plus more distance, if you want to.  At that point, if you like distance, and have it to shoot, and you want the gun to do more for you - build another gun.  Keep this one as your hunting gun out to 250, and target hitting out to 500...  

My $0.02...