So, I just seated the 90grain bullets about 1/8" in the neck (it seemed about the least that could be expected to reliably hold the bullet to and from the field).
The 90 grain Sierra varmint bullet so seated with a top load was the most accurate load I had in my rifle. That is, until I had shot about 2700 of them: at that point the throat had advanced enough so that these short bullets had a *huge* jump to the rifling (and a rough throut it was by then too!). Nothing much helped after that, although the rifle was still reasonably accurate with heavier bullets.
Those Sierra varmint bullets sure did nasty things to groundhogs... :0
jpb