I've been shooting hogs for some time now using a 6.5 Creedmore, and recently decided to start trying a 6.5 Grendel as well. I purchased 260 rds. of factory Hornady 123 SST ammo, along with 200 rds. of new brass...but have no experience with the caliber. I would like to continue to use the 123 Hornady bullets to load in it as I have had good luck with them in the Creedmore, but I'm curious as to what powder to use to work up a good load for it.
Anybody have any advice as to what would be the best powder (hopefully something easily obtained) for it?

30.0 grains of Blc-2 works fine in all my Grendels. AR and bolt guns. 123 and 129 SST

Lots of powders will work for it. One of the very popular ones with 123gr Hornady bullets is 8208. I mostly shoot 129 and 130 gr bullets and mostly use CFE223. TAC and AR Comp are a couple more that have shown good results.

CFE223

Looks like CFE223 is one of the most favored among users, as far as I can find. I guess I will need to find a few lbs. and see what it does. A friend has built a rifle for me, and I haven't gotten it from him yet, but I should be all set by the time I do. Just have to pick up a night scope for this one as well, and I'll have two rifles ready for the porkers.

H4895 is very accurate in mine and 8208 XBR is accurate and faster

I'm similarly just got into the 6.5 Grendel. I was about to put a long post of my experience so far.

The same 6.5 Grendel hornady black worked well for me too at 100 yards, roughly 1 moa or slightly better. I tried Ramshot tac with same 123gr eld and so far the factory is better. It even feels like harder recoil. Based on my limited, one attamept I'm going to say Ramshot tac is NOT the powder for me.