I am the in same boat with 25-06 accuracy, there is no problem with getting accuracy with lighter bullets in this gun(75,87,90), but when you get to the 100 grain bullets (same as yours 100grain hornady spire point) accuracy starts to fall off best I have got is about an inch or so with slow burning powder 52grains IMR4831, if I go to renowned accuracy load of 52 grains of IMR4350 it will shoot about a two inch group. Now that being said, what pressure effects this has on this gun is seen very easy, now just maybe an even slower burning powder would help even more but loss of speed is a concern I didn't buy a 25-06 to shoot it at a medium speed thats not what it is known for. I have done several things to increase my accuracy starting with forearm, bedded it about 1" past the forearm screw with belzona then floated it with silicon rubber from front to back this gives it full length padding it gave me about a half inch or more accuracy, next is the underlug, my lock up was not true to the receiver had a gap on one side at lock-up, in my case I welded up the underlug (filled in the half circle for hinge pin) and remilled so it would fit the receiver square this took about three 12 hour night shifts to get it right. Also locking lug, notched it out to fully engage the under lug (cut a notch in it where it meets the frame so it would stick out further, did not take much off, don't want it to be weak)My accuracy did increase after all this tinkering but I am still not happy with it ,happier but not happy. I have had this gun for about two years and have shot it close to 600 times everything has been with reloads. I have tried several different powders, bullets, and loads, best load I have got for it is 58 grains of IMR4831 behind 90 grain sierra bthp it will shoot 1" at 200 yards, or about half inch at a hundred, 75's will shoot better than this but I would not deer hunt with them.