Some firearms , just want certain styles or brands of bullets. I quit trying to figure this one out long ago! It may be something to do with bearing surface or something of that nature.
Are ya using rifle data versus data designed for a 15'' barrel? I've seen different powder choices and weights listed for my 7-08 Encore that weren't listed for rifles of the same caliber. You may try some round nose bullets also. Some of the rifles that I've owned seemed to like them better than pointed ones. I've got a 788 Rem that will shoot one hole groups with 180 Speer RN bullets. I've not ever duplicated it with a standard bullet. GO FIGURE THAT ONE?
HWD