First off, I see nothing wrong with bedding a base, front and rear especially on a magnum or 30-06 sized case.
Secondly, bedding the rear. How did you do it? was it snugged tightly or what? Sometimes the old FB receivers were milled out of square with the top of the action. First thing I do is tighten the front screws and see how it fits with the rear flat. I have bedded the rear without the screws being tight.