I would propose a theory that as the bullet travels down the barrel it applies one of Newton's theories, every force has an opposite and equal reaction. As rifling imparts spin on the bullet, the bullet causes oscillation in the barrel. Using this idea on your 460, how much does the barrel have to oscillate to cause 16 inches of difference in poi ?
To start out lets assume that your highest poi is caused by the bullet exiting the barrel at the top of the oscillation. And assuming the low poi is caused by the bullet exiting at the bottom of the oscillation. Therefore the barrel is moving a little less than 8 moa each direction beyond the straight centerline of the bore. 1 moa is just over 1 inch at 100 yards. 1 inch divided by 100 tells us that 1 moa at 3 feet is .01 inches. For a 24 inch barrel 1 moa is 2/3 of what it is at 3 feet=.0066 inches. 8 moa multiplied by .0066 is the amount of oscillation needed to cause 16 inches at 100 yards. 8x .0066= .0528 inches Do you suppose your barrel could move 5 hundredths of an inch? These numbers are not exact but very close.
Pretty long story problem. What kind of class do you teach?
You can't fix stupid....however ignorance can be cured through education!