If you don't mind me asking is it an AR platform? That's what the Grendel was designed for.
I've admired the Grendel for a long time, but wasn't aware that their was cheap factory ammo for it (Russian, at that!). That makes it a lot more viable choice, for sure.
Lately I've been sort of smitten by the .277 Wolverine (brass can be formed from regular 5.56mm ). It's not the specialized long distance cartridge the Grendel is, but achieves about 90% of what the 6.8 SPC does, using readily obtainable brass, standard magazines, and unmodified bolts. Just screw in the new barrel and go!