A resent bolt bushing job done for a customer. This is an after photo and some of the procedures . Bushing decreases the size of your firing pin and centers it, you can see a photo here at the bottom of this page of a brass primer before bushing and a nickle plated primer after bushing. It has been known to increase accuracy and prevent ruptured primers on hot days. Also virtually all bench rest shooters make their firing pin approx .062in which seams to give the best results.
First the pin is measured and also the original firing pin hole. This one was a whopping a large 0.074in and the firing pin was 0.0675. The bolt is reamed out and a bushing is pressed in with 4 tons press. Then the bushing is drilled for a smaller firing pin hole. The end result is an almost seamless face with not sign of the bushing at all.
Then the bolt face is trued up with the lugs and the bushing is shaved down flush.
Finally the firing pin itself is reduced to fit the hole to perfection then lapped to ensure absolute smoothness of travel. With the new and smaller firing pin and hole, less pressure is on the firing pin. The amount of force on the firing pin is reduced by more then 20%. Now the shooter can reduce firing pin spring tension, if he so desires, and get a much easier bolt lift.