GG, I am not sure that this will help you with that rifle or not. However I will throw it out there anyway. When I was working up the initial loads for this rifle years ago, I was having no luck getting decent groups with Noslers. I was seating them out close to the lands. I tried all of the "best" recommended powders and such, but nothing. So on a whim, I started to seat deeper. I got somewhat away from the lands and the groups shrank into a nice ragged hole. With the BT, seated to 3.250 OAL, I can drill a nice ragged hole out at 200 yds with no problems. So, I tried several other bullets without changing the seating depth on the die and they all shot right there also. not so much in the same area, as some did hit elsewhere than POA, but they would still grouped great none the less. So basically I have never changed my die except for the 100gr Sierra's, which I have to seat to, 3.150 for whatever reason.
Just a thought but it might make the difference your looking for. Sometimes they might just like a jump start. The ones I shot above were using 56.5gr of RL-22,Win cases, and Win-WLR primers, seated to 3.250 OAL. The velocity however was only 3050, and I feel I can improve on that some, since I am getting 3150 with the 115 PT's. The rifle is a Rem. BDL, wearing a Fajen laminate stock. Nothing else has been done to it. The last two shots there together, are pretty much the norm for this rig out at 200yds with the 100gr BT's and 115 PT's also. I know this is uncommon for a factory rifle but I ain't complaining.
Hope this helps, I know how frusterating it can be. I will be giving them a decent run over LD weekend and will report back after trying a different powder or two.