Since ~2012 and onward, the 6.5 Grendel is the one to get between the two. The first ~10yrs of their life together on the market, the 6.8 SPC had the upper hand for market support and availability, but once Will Bill released the trademark for SAAMI compliance standardization and riding both the boom of the AR following Sandy Hook and the coattails of the 6.5 Creedmoor and the long range shooting boom, the Grendel has flown past the 6.8 SPC for market support and popularity.
I have been a big fan of both since the beginning, and still have two 6.8 SPC rifles, but if I didn’t have such an abundance of brass, and if I hadn’t converted all of my 6.5 Grendel brass over to 243LBC, I’d abandon the barrels to the back of the safe and swap both rifles over to 6.5 Grendel… or 6 ARC.
Ballistically, there is really no practical difference between the two, and the lines about “6.8 SPC is better for hunting, Grendel is better for long range,” or “SPC is optimized for short barrels, while Grendel needs longer barrels to perform” are all just tired, tired, tired exaggerations which mean little more than absolutely nothing. I’ve hunted with both, shot 1,000yrds with both, had both in short barrels and long barrels… it’s easier to feed the 6.5 Grendel, and more, better bullets are available…
But the market support is overwhelmingly in favor of the 6.5 Grendel, which is what makes the real difference between the two for owning either. Better bullets, more availability of brass and bullets, more options for barrels, bolts, and mags all favor the 6.5 Grendel, and will remain so for the foreseeable future.