Adam,
BLUF, since Alexander Arms allowed the Grendel to become SAAMI speced and no longer requires royalties for use of the Grendel name my following recommendation is not the issue it was at one time. However, before you commit totally to this look at the .264 LBC (Les Baer Custom) specs and compare to the 6.5 Grendel. A Bing search will give you a lot of reading on the subject.
That said, IMHO the 6.5 Grendel/.264lbc is about the most perfect chambering for the AR15 platform and I'd be more inclined to go with the 6.5 Creedmoor, 260 Rem, or 6.5X55 on the Handi platform due to the Handi's ability to handle higher pressures without cartridge length limitations. Best bang for your buck. Now, just so I don't get flamed too bad for my opinion, one of the draws for the Handi is the ease in rebore/rechambering and stubbing for the nonstandard caliber of choice. Have fun.
Shvlhead.45