I will agree that installing shims in an action takes patience & finesse. However, I have installed some of Lance Shivleys shims in a few of my guns, and like what they have done.
Yes, I ruined a set of Blackhawk shims once. I attribute that to my state of mind at the time. (I shouldn't have been working on anything mechanical that day. I had just heard about the loss of a friend, a helicopter pilot in the Cav, in Afganastan.)
But the follow up set went in just fine.
But before adding shims etc, as noted, a simple smoothing of the rough areas, while NOT changing angles will do a LOT for any action.