Larry,
I bought Veral Smiths little Blue book that has cost me several thousands of dollars to date. My first purchase was a 700 Remington LSS in 30-06. First thing I did was to free float it. Next thing I did was try to shoot high velocity cast in it and I stuck the bolt. 300 rounds later I started HV work again.
I used the 56 grains of RL 19 that I always quote as this is where groups peaked. Group sizes were about 2 " with defective fliers running out to 6". So I bedded it with 2# of pressure. Groups came in a little to let's call it 1 3/4" and fliers stayed about 6". I upped the pressure to 4#. This time groups stayed the same and fliers came in @ 4". Hmmmm I says. So I upped the pressure to 8#. Groups came right in to about an inch and fliers now are 1 1/2". That's a bullet with the grand canyon running up the side.
My "guess" is that a bad bullet or load causes a rotational change that alters timing and that change alters barrel vibration causing the bullet to exit at wild points. Uncontrolled, that vibration is going to get worse the higher the velocity goes. Bedding pressure minimizes that effect. The only time I get truly wild fliers now is when my lube thickens and sizes down my bullets enough that they DO let go of the rifling. Then every shot is a flier, good bullets and all. But based upon my results above, I disagree that bad or unbalanced bullets are the cause of most fliers. Otherwise bedding would show no change.
MOST of all cast bullet damage is done from internal ballistics while the bullet is still in the barrel, and not from external ballistics at least until longer range. Even at high RPM.