this will be my first attempt. I bought the Ed Brown Ambi Tactical.
I would like a step by step explanation for a beginer maybe with some pictures? I have the Ed Brown Book but it is not very detailed on that subject.
Short version goes like this (sorry, no pics available):
With unloaded gun, remove thumb safety, m/s housing pin & lower m/s housing by 1/4" to allow grip safety to come off. Reinstall m/s housing & pin. Now that you have the thumb safety off, remove the plunger pin assy., cock the hammer & reinstall thumb safety. Looking in through grip safety area, observe how the thumb safety "block" swings up (as the safety lever is lifted) to block the bottom left leg of the sear. This keeps the bottom of the sear from being moved rearward by the trigger & disconnector foot. Now remove the old safety and compare the "block" to the block on the new safety. You will note that there is an additional flat on the forward side of the "block" that was cut when the old safety was fitted. That point is where the engagement cut is made to fit the new safety. Comparing the old one again, cut the (same angle & location) flat into the new one. Every 5 or 6 strokes, try to put the new safety in the gun. Note that the new safety will not swing up into engagement yet. Keep filing & testing as above, until you reach a point where it will just fit in, but is still tight. Switch to a fine Arkansas stone & continue same procedure. Look at the engagement face you are cutting every time you test fit it and compare it to the old safety. Look at the mark that the sear leaves on the flat. You want an angle that gives a good bit of surface contact, when the safety is engaged. Correct the angle if you have gotten off. Stop stoning the minute you get it to go in and swing up into engagement without forcing it. Test it for blocking the sear by pulling the trigger hard, while the safety is on. The hammer should not fall. Then let go of the trigger, flip the safety off and listen closely, while you pull back on the hammer. You should not hear a tiny "click". If you do, it is an indication that the fitting pad on the safety has been cut too far and the sear is starting to move out from under the hammer hooks, when the trigger was pulled. If you do not hear a "tiny click", you are finished fitting the engagement portion and are ready to move on to fitting the plunger detent, the R.H. half to the grip panel, melting the back corners. I think this was the part that you were asking about. God Luck!