i use the same bullet and powderin my m77,4064 seems to be my go to powder.i think my load is a little hotter 36.2 sounds right without looking.works well up here in the northcountry on whitetails.largest i have killed with the 257,weight wise was 175 dressed.i don't know how big a b-tail is but do your part and i think you'l be fine.depending on your shooting range i would prob lower it to 1 inch high @100 for 200 yd average.i site mine dead on at 100 as i rarely shoot past that, 150 would be a long shot here.most deer we kill under 50 yds.good luck adker