None that I can see, except for ammo for both. Make your choice and stick with it.

The 6.5 has ammo available from Alexander Arms (spendy) and Wolf.

The 6.8 has ammo available from SSA (Silver State Armory) in Morton, WA, as well as Remington and a few others. SSA brass is small rifle primer, Remington brass is large rifle primer. (Two formats is confusing, make sure you sort brass correctly.) No Wolf available.

Both calibers have a lot of projectiles out there, with the Barnes TTSX being some of the best ones IMHO, Accubonds coming in a close second.

I have also been able to find Remington 115 FMJ's, so I bought 3,000 for the 6.8 SPC. (6.8SPC was developed to be a replacement for 5.56x45) Lots of bulk projectiles available.

6.5 FMJ's are SPENDY, so be prepared (Lapua). Cheapest ammo by the box is $13 for Wolf through AA. Don't see any loaded FMJ offering by anyone. Pretty expensive blasting/training ammo. Not a lot of bulk projectiles available.

I handload everything, so I bought 1,000 pieces of brass from SSA. Relatively low pressure round, so the cartridges don't get too beat up. Easy round to load, good accuracy, and the boys have taken 3 deer to date with our 6.8.

6.8 SPC might be a better choice if resale is important. Probably more universally accepted.
Grendel has more poop.
Looks like store-bought ammo is similar in price with more support for 6.8.....$1.00 per round......ouch.

6.8
http://www.targetsportsusa.com/c-93-68mm-remington-spc-ammo.aspx

Grendel
http://www.targetsportsusa.com/c-928-65-grendel-ammo.aspx

Don't overlook the 6x45....basically a .233 necked up to 6mm. Little need for propietary modifications or cartridges.

Handloads even the score between 6.8 & 6.5. Heavier bullet choices with the 6.8 make the choice clear, along with greater overall range of bullet choices.

Powder capacity is greater with 6.8 than 6x45, larger bullets, greater FPE at the destination.

One cool thing with 6x45, just form your own brass from .223 (5.56x45). Same with .300 Blackout. Also use regular bolts for .223/5.56. Again, downside is downrange performance (FPE).

Accuracy with all out of AR platforms is excellent.

6.8 is a good choice.
http://68forums.com/forums/forum.php
A 1x-4x Vortex gives you the best of both.
Illuminated CQ both eyes open @ true 1x and then you can dial up to 4x for longer stuff.
There are two reticle choices and the price is fair.
Bobro or Larue rings/mounts.

I'm over at 6.8 forums. Been a long time though. If you need a primer on reloading 6.8, swing on over once you get yours. Hopefully I'll have a new can that I can "use" for that rifle by then.

where can you buy a can and do you need a federal license to own one?

Discount guns..Wades

Yes...a federal tax stamp

East County Guns has them.

Form a trust, as the GH Sheriff won't sign off on one. Take copies of trust papers to gun shop. Buy can, fill out 2 copies of Form 4. Send in with $200. Wait 60-180 days to get tax stamp. Head down to East County Guns. Pick up can. Shoot in peace.

That's a very high quality AR right there

Redd----Dogfish, as usual, knows the dance step by step.

Try Doug at Cameraland for Vortex.

Seems like the short 6mm - 6.8mm is getting a lot of attention these days. Flavor of the month sort of thing.
Here's a 6 that's made from a necked down and blown out Grendel :
6mm DTI
http://www.predatormastersforums.com/forums/ubbthreads.php?ubb=showflat&Number=1633906
It gets the 6mm pills moving pretty good.

That is a nice new caliber. Fun playing with stuff that isn't "off the shelf".

If you think that Noveske upper was neat. Just wait until we can play with a Noveske attached to that same lower, sporting a 7.5"-10.5" barrel. 14.5" will be so "yesterday".

SBR's (short barreled rifles) are next year's goal.

Went to the Judiciary Committee meeting on HB 1016 today. The bill continues to move forward as apparently the bill was moved to the exec committee today ahead of schedule where it received a "Do pass" rating. Thanks Senator Carrell for advancing this ahead of schedule!

Rules committee is next, then the floor for a vote, and then 90 days after session, shooting gets A LOT QUIETER!

Passed out of Rules Committee and it has been placed on the second reading schedule in the Senate! One step closer.

Passed today 47-0. Next stop, the queen.

Then we'll get to shoot quietly 90 days after the end of the session.

I was invited to the signing of the bill this Monday. Looks like as of July 23rd, it will be law. My trust is done, so I am ready.