I've run two .308's with both Vaget and Re-15 using various 150 gr. bullets.
A typical long range target load is 48 grs. of Varget and somebody's 155 gr. match bullet with WW cases. I've used 47 grs. of both Varget and Re-15 with several 150 gr. bullets. Maybe your cases aren't up to spec.
H4895 is one of the most accurate powders I've ever used in the .308. I've never run it full throttle with 150's, but I have with 125-130 gr. bullets. But either Varget or Re-15 will push them faster.
If your loads aren't consistant, you might try a hotter primer, CCI 250's WLR's, Fed 210's.
I'd recommend different brass as well. E