don't know what your charge is, but I have found that W 748 has been the accuracy champ with the heavier bullets...
I am at higher than the 2250 mark shooting 140 gr Speer and Hornady bullets. you can't get enough W 748 or BLC.2 in a Grendel case to over pressurize it...
with the 140s, I am running a charge of 29 grains.... 129 and 130 gr bullets, I am running 29.5 grains...of 748.
123 grainers, and 120 grainers, I am running 30 grains of 748...velocity is in the 2500 fps range with those...
one batch of Hornady brass, I am on the 15th reload of that batch of 10, as of yesterday....Today it will be on the 16th. Primers are still tight.
I neck size, bump back the shoulder with a body die and anneal each reload.
I have found quite a bit of load data on the Grendal, and also reference some of the data from 7.62 x 39, for powders, and go from starting charges and work up.
also look at 6 x 45 data and work up....also reference 6.5 x 223 Single shot pistol data as well at 6.5 x 39 data from some older reload manuals.
mine is a bolt action Ruger American Predator, 22 inch barrel...
I am finding that about any powder beyond 4198, its really hard to over pressurize the Grendal Case...
it is close to being a bolt action 30/30 with velocity potential.
