My story is almost the same as yours, but with a great end. I bought my Fierce 28 Nosler 2 years ago. Could not get it to shoot groups. tried all kinds of loads - cases, powders, bullets. Sent it back to Fierce, they did a deep cleaning, shot it and sent it back with the 3 shot group at .3875" group. I talked to them and they said they only guarantee that group using the components they used, including the OAL. Also, they explained to me that their guns are made with very close tolerances to guarantee an accurate first, cold bore shot, since they are made for hunting, not repeated target shooting.
Using their load, 168 Berger VLD's, H1000 powder, I shot the same 3 shot group. After 3 shots, the group spread out to 2-3". I went out to Fierce for their long range shooting course. They guaranteed they would have that rifle shooting a mile. Sure enough, that rifle shot every target out to a mile. The more rounds through it, the better it shoots. So I would say, 1) use their load exactly 2) never shoot more than 3 shot groups to see .5 MOA, 3) The more rounds shot the better the rifle shoots. I was also using a Thunderbeast suppressor.