The grendel is slower than a 223. Lighter bullets obviously can close that gap some, I'd have to look up data to see how much.
I used Hornady factory ammo to get it on paper & zero'd at 100 yards, will eventually result in another 100 pieces of brass.
I bought a variety of Hornady bullets to try loading, with new Hornady brass, AA2505 & CCI 450 primers to start with.
I do have some other powders on the shelf, such as some Varget, but I hesitate to mess with any that I don't have much of when it's still hard to replace. I also have a good stock of other small rifle primers, but the 450's took a while to get. When I finally found them I was able to buy 1000.