rear sight out of plumb

[Lumpy Grits]

If your rifle is capable of 2" grouping @ 100 yds, read that as MOA rifle, then 4" @ 200 yds is possible. Then again, it's possible your rifle/load is NOT a MOA combination. Whereupon, even a "slight" breeze/windy condition can appear to scatter you bullet-holes around.

Also, the wind conditions at the muzzle of the rifle may not be the same @ 200,300, 400 yds. downrange.

Just tryin' to add something here. I do not know it all!

Jim, 2" group @ 100yds =2MOA
I still think the front sight got bumped somehow.
One other thing to check, is the muzzle crown under some strong 'glass'. To see if it got marred somehow.
Gary