The major difference in power with the 6.8 and 6.5 is when barrels go under 16". The 6.8 was originally designed for a 14.5" NFA barrel, and the case design and powders used tend to add diminishing returns beyond that. The 6.8 is definitely the better round in a 10" PDW, exactly what is being sold to a Middle Eastern government for Royal protection.
It's not that the 6.5 can't be chopped down, but the large ratio case to bullet diameter from the AK has proven out to be a better long distance shooter - using typically slower powders, the 6.5 achieves the same velocity in a 20" inch barrel as the 6.8 does in a 16". What it excels at is having a longer bullet to go with the short fat case, so the aerodynamics for long distance flight are better. The 6.8 compromises that with a longer narrower case which leaves less room for the bullet.
There's the reasons behind why the 6.5 was invented by a long distance shooter, initially tested on long distance range matches, and where it still demonstrates some serious potential. The 6.8 was designed by Special Forces with the Army Marksmanship Unit to beef up power at combat range, out to 300 meters, and it delivers in a light short barrel.
They were never intended to compete for the same job, although a lot of newbs confuse them. It's like the constant arguing about the Sebenza vs SNG, just because something has the same materials and price doesn't mean it does the same job.
What I find funny is the hypersensitivity by some Grendel shooters when any aspersion is made about the 6.5 not being optimal for a short barrel short range gun. It's not the absolute top dog, no, but that doesn't mean it can't be done. You just might be giving away a bit of performance, and frankly, it's something that a good handloader might be able to tweak back.
Some of us 6.8 guys do know what we are talking about. They are both fine calibers, but they were never intended in the beginning to be competitors. Fanboys bring that into the game with they identify caliber to masculinity.
As for ammo, we've heard complaints for years about it being pricey. Guess what? IT'S NOT SURPLUS. You can't get overruns, rejects, and armory sell offs like you can with military calibers. It's all new ammo for the market with no government subsidy. You pay the shelf price like any other. So, if you want to shoot a lot of it, shoot reloads. Reloaded ammo is at least half the price, and a good entry level kit at $200 will pay for itself in a year or two of shooting. Plus, you aren't at the mercy of a restricted system of distribution where just in time logistics attempt to put a few boxes on the shelf every week. You can make that in an hours work reusing those expensive brass cases and simply adding back the consumable parts.
Price 30-06 or .45 surplus lately? Not really available much anymore, tons of it was shot up in the 70's and '80s when governments sold it off changing to new calibers. The same thing will happen with 7.62x39 and .5.56. If you want to shoot something designed for hunting tho, most states require hunting ammo, and that means you are right back to buying commercial hunting ammo off the shelf. Don't deceive yourself about that.
