You need to be real careful about paying attention to "someone." Now while that warning should include me & all the internet people, let's start with the basics.
It seems like you are not full-length sizing your cases. How do you know that the case isn't too big at the web or too big (diameter) at the shoulder, rather than too long at the shoulder? And while brass may spring back a little more when hardened by multiple firings, I seriously doubt that annealing the shoulder & then bumping it will solve your problem. You could test that by bumping the shoulder a bit more right now -- like .002. Differences in springback between virgin brass & many-times fires brass aren't that much.
So the first thing I would try is full-length resizing.
If you insist, annealing isn't that hard, search the archives, but better yet, get a good book that covers the proper technique. Howells DESIGNING AND FORMING CUSTOM CARTRIDGES is a good source. There is also a lot of bad advise on annealing out there (more "someone"); done wrong it ruins brass, and done really wrong, can be dangerous.