The SHORT answer would be NO. In checking Hogdgon's web-site nothing was listed in the powder you were using for a 123 grain (gr. not g.) bullet. Also it would appear from the listings they do have (for other powders), that 28.5 grains (not grams) of powder may be a bit too hot. But I can not comfirm this since there is no listing for this powder in ANY 6.5 Grendel loading for ANY weight.
I do not know where you got your load data from, but if it was me I would break them all apart and start with a new pound of powder that is recomended by Hogdgon for that caliber and weight bullet. H4198 or IMR 4198 should work well.
As to that bullet, the only 123 grain bullets I am aware of are for the 7.62x39, and are you sure those are the correct bullets for the 6.5 and are not in fact the .310 for the AK-47 or SKS.
Si vis pacem, para bellum
Last edited by Jim243; January 29, 2012 at 12:28 AM.