what do I chose? Please help. I like the idea of the 6.5 and it is on the same platform, but 308 is everywhere.
What to do. Would like it for hunting and possible comps to 600 yards

thanks

Grendel for me.

There is nothing I would use .308 for that the Grendel does not perform as good or better by just swapping upper, bolt, and mag with an existing AR lower.

If you're gonna' hunt large game beyond 300yds the .308 will hit harder.

If you're competition target shooting out to 600 a dedicated heavier rifle in .308 might be slightly better on paper ( 178g ELD), but then I'd go with a larger 6.5 round anyway (Creedmoore, Lapua, .260 rem etc.).
A run'n'gun or PRS competition with longest shots not beyond 800 yds the smaller AR platform might be better for mobility and speed.

My opinion, ymmv.

Edit: PS:  I have no problem finding Grendel ammo or bullets for reloading.

Do you mean Creedmoor?

Precision I'd rather have a Creedmoor... But I also have a 308 for ammo availability

well I meant the 6.5 Grendel, but now that you mention it, I could do a Creedmoor and also have a spare 308 barrel or upper. best of both worlds I guess

If you're going to be packing the rifle around while hunting you would probably appreciate the the lighter weight of the small frame Grendel.

Since messing with the Grendel I hardly touch my .308s.   Just all around more fun to shoot and it does just fine out to 600 yards.

I have a Grendel and Creedmoor,  6.5 Creedmoor.  I like them both I would say about equally. I don't have a 308. I do have another large frame almost ready to assemble,  but that will be a 6mm Creedmoor.

Even when I start building my bolt guns they will be in these calibers. Semi's limit some capabilities due to mag length restrictions and the like,  but they perform well enough for me. If I really want to push any of those calibers it would/will be in a bolt gun.

Both the Grendel and the 6.5 Creedmoor are accurate and pretty easy and mild to shoot. Can't go wrong with either in my opinion. I do like that the Grendel being in the small form factor of the AR15. That and the AR15 being far more standardized than the large frame AR's make it a lot easier to build and/or tune.

I've owned a lot of different .308s, but was continually frustrated with misses in competition as the distances got past 400yds in full wind values that were 10mph or higher.

I've never had problems connecting at 500yds-and-in with .308 in less than 10mph winds.

.260 Rem was becoming more and more popular for long range rifle, so I got several .260s and am very happy with the performance.

I initially looked at 6.5 Grendel as more of a test, an experiment, seeing what performance I could get out of the AR15 without having to lug around the AR10.

It started growing on me once I saw that I had repeated, predictable hits at 1200yds from a 16" AR15 with factory ammo.  That go my attention.

I shed all my .308 components and rifles after that.

Now I have 6 Grendel ARs, 1 Grendel bolt gun, and haven't shot my .260 Rem in years.

Big reasons for not shooting the .260 Rem in a while is I only hand-loaded for it since it's a gasser, and there weren't any factory loads that I was willing to risk it with.

Ammo prices for .260 have traditionally been very high also.  The only factory load I'm looking at now is Hornady's 130gr ELD-M, which appears to be a great load, but I still don't know how it will behave in my rifle.

I've bent at least 3 firing pin retaining pins in the .260, pierced primers, with 3-5x firing brass life that requires regular trimming.

The rifle weighs 14lbs as well, more difficult to pack, shoot, and carry.

My 22" Grendel is still supersonic out to well beyond 1000yds, as are my 18" guns.

I have .308’s in both gassers and bolt guns. I shoot 50 times more ammo thru my one 6.5 Grendel upper than all my .308’s combined. I stopped shooting my MK12 Mod0 upper because of the Grendel. The Hornady Black ammo is less expensive and easier to find than the .223 match ammo I typically shoot in the Mod0.
The Grendel whacks steel at 330 yards much harder than the 77 grain .223 does.

Me and my nephew were shooting my Grendel(123g ELDs) at 540m and then zeroing his .223 bolt rifle(55g Blitzking) at 200yards. The Grendel and .223 sounded similar even with an almost 400yard difference.

I am considering a Grendel barrel and bolt to swap into my SPRish AR for some long range shooting.

What is the best value in a barrel and bolt that would be precision oriented and should I go 18 or 20"?

I would go with .308 personally. Widener's has been selling IMI 7.62x51mm brass for under $300 per 1000. .308 match bullets don't cost any more than the 6.5 variety.

My 6.5 Grendel Lapua brass cost more than my loaded round for .308. I cringe every time I lose brass to the weeds or it gets damaged during ejection.

If you go with 6.5 Grendel get E-Lander's magazines. They're the only ones that have worked reliably for me right from the factory.

I have both because you sort of need both if you hunt medium and large game. Either one is good for a 400 yard kill but that's about the limit. In fact as a matter of ethics I won't take game over 300 yards.

If you're just shooting paper then I personally feel it's a wash. The .308 by name alone sounds like should outshoot the Grendel but mine hasn't yet. The Grendel has a little less kick but both can be tamed with an adjustable gas block. Typically the Grendel hunts best with an 18" barrel while the .308 is best with a 22 or 24. The .308 is a large frame AR-10 (LR DPMS) rifle where a Grendel keeps you in the AR-15 platform. The benefit there is that you can use one lower and shoot both .223/5.56 and 6.5 Grendel and a few others. In the AR-10 the best round overall in my opinion remains the .308

Hunting what?  And at what ranges?
All 3 will work at 600 yards.  And you won't notice much difference.  308 and 6.5 will kick harder especially in a hunting weight rifle, you don't want to be lugging around a 10 lb gun when hunting if your going up and down mountains.
For game over 300 lbs the 6.5 creedmor and 308 do hit harder, at normal hunting ranges (200 yards) the 308 is going to hit harder than the other two as the ballistic performance of the 6.5's is not noticeable until you get to longer ranges.  
The 6.5 grendel and 308 can be shot a lot cheaper than the 6.5 creedmor.  Also the grendel will be much easier to keep at a good hunting weight in a traditional AR 10 type of SA.(browning make the BAR which is just as light as most ar15's)
So my choices would be
If shooting medium sized game 6.5 grendel.
If shooting large game 308 or 6.5 creedmor.

A Weatherby Mark V weighs in at over 8lbs empty so you can easily be at 10lbs after you finishing dressing it up. If you want a ethical kill distance of 600 yards you really want a long distance hunting rifle like the Mark V in 6.5-300 Weatherby Mag. However, at nearly 5.00 per round your range time will be limited to what you can afford. When I speak to ethical kills, I'm talking one well placed shot will cause a clean kill. If you're fighting in combat, a wounded soldier is acceptable but when your hunting, a wounded animal is not. This is why I have both a 6.5 Grendel and a .308 and use them appropriately when taking game.

He said hunting and target to 600.  I am assuming he did not mean hunting to 600 yards.  In that case I wouldn't use any of the 3 cartridges he mentioned.  In my opinion shooting game at 600 is going to really be pushing it for any of them.  If thats the case a bigger 6.5 or magnum 30 caliber is called for.

Absolutely agree. I wasn't 100% sure of his desires which is why I tried to stress the ethics behind long range (300 yards or more) game hunting.

agree with everyone on here.
i love the profile of the ar15 would love to stay in the profile but with the 308 I could use that in a restricted class comp, switch it out for 6.5 creed and I have a better caliber to work with
I like the Grendel too, just hard to choose
Depends I guess on cash and what you want to invest in each platform. Both 6.5s are great flat shooters

Oh I agree completely.  I am not a fan of shooting unwounded game at 600 yards.  I can see 400 but 600 get closer!  But thats just me.

I think I will cave to the 308, I don't think it is a bad thing to have a 308 laying around and in the Commie state of MN it might come in handy

Grendel doesn’t make a lot of since to me. I considered it for a while but I’m passing for the moment. 6.5 Creedmoor factory ammo is less expensive and there are more factory loads available. Creedmoor doesn’t require a weird off the wall magazine. If you’re not shooting beyond 500 yards and would benefit from slightly milder recoil then maybe the Grendel would be a good choice but Creedmoor is going to smoke the Grendel at longer distances.

The Grendel fitting in an AR15 is the main benefit. How and where is Creedmoor cheaper than Grendel ammo? Maybe equal.

Yeah going into the ar10 platform is a big change in money where as the 15 is a better fit
Jesus maybe I should just flip a coin at this point

I would 6.5 grendel. If going AR10 I would pick 6.5 Creedmoor over .308

I dont have a situation where I would pick a .308, there are just much better rounds IMO