Nomercy, I completely understand your POV. But, you suggested ensuring he had a good rest and then jumped into your FOV BS. You didn't even mention his scope mounts could be lose, or it may just be a bad scope, you jumped right into he doesn't have a powerful enough scope.
By the OP's description it sounded most likely A: He wasn't using a good rest, B: He just had a bad range day, C: The scope mounts are out of whack, D: The scope is junk, E: The gun isn't accurate in the first place, F: Even though he tried 2 types of ammo the gun still didn't like it at all, or G: Any combination of the above. He was shooting 3" groups at 50 yds. If you are telling me that even if his rifle is actually pulling of 1.5 MOA groups, he has >4 MOA of error because he isn't using a powerful enough scope, GET OFF THE DRUGS. Heck lets all just shoot for accuracy and strap big scopes onto our guns, because obviously nobody can shoot a 1" group at 100 yds with a 4x scope because nobody can shoot a 1" group at 1000 yds with a 30x scope.
Or consider a 3-9x40mm scope. A 1" group at 100yrds with that 1.75-4x scope is the same as shooting a 1" group at 250yrds with a 3-9x40mm scope.
I don't care how you look at this (and I am saying this understanding your % of FOV BS), but they are not the same thing. The first one is VERY POSSIBLE with a large percentage of rifles produced today, the second, if you are able to do it is likely a fluke or produced by a custom rig.
Your explanation may have some merit, but I can not believe the OP's problem is he is underscoped. I have shot far too many 1.5"-2" groups at 350 yds to believe that a 3-9X scope isn't adequate for that range. I place far more weight on the quality of the glass than the magnification.