I have a 5.56 but think I want a larger caliber for plinking and possibly game and maybe getting into long range shooting out to 500 at steel.

Should I just go .308 or consider other calibers? I think price of ammo should come into consideration as well as ballistics performance. Lower consideration might be a lower that can work with different cartidges depending on the upper but not a big deal.

Id look at a 6.5 Ammo is a little more but I like it.

if 6.5 then which cartridge and why?

Keep your 5.56 for shooting steel at 500Y. Load some 73gr ELDM and you can shoot at 800Y.

Grendel.

Grendel. (just get an upper that you swap out) The BC of the bullets in this cartridge allow it to stay supersonic out to 1200 yards (Hornady AMax). You can also get plinker rounds for about $.50 per round. The 73 gr. ELDM in a 5.56 may work but you may have to get a barrel with a faster twist rate.

P_102

if you can afford it, 6.5 creedmoor,

if you upgrade to a AR10 - get a light weight one like the DPMS gen2.
I have a regular AR10 in .308 16" barrel that simply shoots lights out but with scope is over 10lbs. Plus you really don't need a heavy bull barrel if its going too be used as a hunting rifle

308

I settled on 9mm, 5.56 and .300 AAC for my own uses.

I've owned them in .308 and 7.62x39 as well.

Good luck with your choice.

The only AR I had was a 5.56. I wanted more energy and the ability to keep that energy to 500 yards. I crunched numbers, and looked at the cost of several options. Due to the nature of energy delivery, the huge amount of brass that is widely available, and the huge amount of bullets that are widely available, I got back into the .308 business, after being out of it for 3 years. Fact of the matter is, the 5.56 and the .308 are military cartridges, therefore there is a plentiful supply of brass for both.

I have spotted for several 6.5 Grendels, and they have flown just fine to 800 yards, shooting very precise, but it is impossible for them to deliver the energy of the good ole .308. The 6.5 Grendel is a great little cartridge, but I wanted more punch on feral hogs.

Agreed 100%. If you don't intend to hunt with it the Grendel is a pretty flat shooter to 500 no problem. The 308 will do that and include the energy. 308 is AR10 and requires a complete new rifle. The Grendel requires only an upper swap of the 556 you already have. 2 pins out, 2 pins in and done (maybe a different mag too). Of course like was said earlier, you could shoot heavier bullets to 500 in 556/223 and give me that extra money.

Depending on what you are wanting to do. 308 if like Fireman you are wanting to engage hogs at 500 yards Grendel if just wanting to shoot 500 and still drop hogs out to 400 yards or so. (Grendel has more energy at 400 than a 243)

For plinking and steel, follow the other advice (if you have the barrel twist) and shoot heavier .223 loads.

The 6.5 Grendel, 6.8 SPC, and .300 BLK are your main choices if you just want to swap an upper. If you're not an amazing shot, I wouldn't recommend any of these past 200-250 yards for game, as the energy levels just aren't there.

If you're really going to hunt with it I would suggest stepping up to the AR10 platform and going with (in order of my preference only) .308, 7mm-08, 6.5 Creedmoor or even .243. The new Savage MSR 10 can be had in .308 or 6.5 and doesn't weight much more than an AR15. The DPMS Recon GII is another option, as FJG mentioned. Either of those would work well. If you don't mind extra weight, you can get a PSA AR10 for about $600-700 right now. There are other options too.

300BO or 6.5G

How much energy are you wanting on target?

of course, you can never go wrong with the increased energy of a 308 out of a AR-10. However, my humble opinion is that it is harder to shoot an AR-10 well, and they are considerably more of a PITA to tote around.

My suggestion is 6.5 Grendel. It's NOT a 308, but comes in a smaller package with lighter recoil. It's more fun to shoot, Hornady box ammo is pretty cheap, and it's got plenty of power for range fun out to 500 and hunting a little bit closer.

I am very much a fan of the 6.8 SPC especially in the AR15 category of choices. Vital shot out to 200-250 is lethal but much further you lose a lot of Ft pounds. I like it bc its light, deadly and ammo is plentiful. There is no doubt the AR10 platform is a step up especially for 200 plus yard shots. 308 with 178 gr AMAX is catastrophic on hogs.

Can easily take an AR10 in 308 out to 800 with good optics.

I failed to mention, another factor.

As far as equal bolt face goes, .260 Rem, 6.5 Creedmoor, 7mm-08, and .308, my favorite is the 7mm-08, no doubt about it. However, AR platforms in .308 Win were more common to find.

Can always get a 7mm-08 barrel and swap it out

I am tempted.

Why do you favor 7-08 over 260/6.5C?

Oh no you didn't

Yes he did!!!!!