Bushing the firing pin is fairly simple with black Lock tite. You turn the end of the firing pin down to .125 with a shoulder that stops the pin on the frame or bolt, as normal. Then drill the bolt face with a flat end mill bit to accept a .250 diameter plug, not a hole through, a flat bottom pocket, with a plug that has .125 hole in the center. The trick is to make a flush to the face pocket fit, using the black lock tite to hold the plug in place. The black has 6k psi shear strength, once set the plug is not coming out. The 1/8” or .125 diameter gives you a smokeless diameter firing pin. Just make sure the firing pin fits freely and the return spring works correctly. Explaining it without my drawings, is not precise. As I am describing by recall, I duplicated the diameter of a 700 Rem firing pin tip. Pretty much any smokeless firing pin and matching bolt face hole diameter would do the trick.
This is what my 357 Super Mag, 225 WM, 218 Bee and 222R Cadets have had done to them. If you run the pressure up to a smokeless level, the BP firing pin hole will cause the primers to flow back, locking up the action.
If you have any questions just drop me a note.