Thanks for the replies. I'll take each in turn.
I agree with your estimate and I'll calculate the force needed to produce such a bend. The bend seems pretty much to me, but it is not trivial to estimate exactly what force is available.
In answer to what classes I teach, the answer is that I've been a university Physics professor for 50years (and still am) and as a result I've taught pretty much everything from beginning undergrad to advanced grad courses.
I agree that it pretty much has to be vibration. The odd thing is that the rifle is a Weatherby MarkV and as such has a free floated barrel. It seems to me that it is difficult to get that to vibrate only vertically. It certainly won't happen as a result of bullet alignment with the bore. I think the upward recoil the Weatherby stock produces must be the ultimate cause. My scope will adjust enough to handle the difference easily and that is what I will do. I'm using the 300 grain for practice because they are cheap. Obviously I won't use them for hunting - probably won't hunt much with this gun anyway.
Another interesting fact. Today I ran the same kind of experiment on my .416 Weatherby MarkV. It was slightly different in that I used the same bullet, but very different powder charges. 350 grain Speer with charges of 85grain RL22 for 2190ft/sec, 110g RL22 for 2660, and 120.5g for 2840. In this case the POI are in the expected order (85 lowest, 110 next, and 120.5 at the top) but again the spread vertically is too large (about 14"). The group sizes were larger, but that may be due to a very strong wind shaking me around a bit. The results for the .460 were the same as before or a bit more (18"), but again the wind may have been responsible.
A great suggestion and one I am going to try. I considered doing it today, but the wind was so strong I decided it would introduce too much error.
Thanks to all of you.