Mach... here's the reason they're not doing so well at 400 yards... I made this with MS paint... so overlook the crudeness. :o
Lots of folks would say that the bullet does not change it's orientation to fly tip first on the downward part of the trajectory curve... however, if that was the case, you'd see oblong holes in the target at extreme range, and alas, you don't... the holes are nice and round just like at 100 yards. So the bullet *must* alter it's axis to fly tip first.
Pistol bullets, or even deck gun bullets from large ships are about as big around as they are long, so they don't really turn into the wind like long range rifle bullets do. You can hold a paper airplane in front of a running fan and see that unless it turns nose first into the wind, it will easily be pushed aside. Not a perfect analogy, but this is basically what a bullet flying into the wind is going to try to do; it'll try to fly tip first.
Over stabilized bullets resist this needed axial change, just like a spinning gyro-scope resists having it's axis changed.
It might be supposed that 55 grain bullets won't group at 400 yards due to wind, but that's not the case. 22 caliber 55 grain bullets, if not over-spun, will group at extreme range.