I replaced a firing pin in a remington Mod 12c. I installed a new one and was getting good contact on case rim.But locking block/bolt would not come out of ingagment after being fired due to the hammers pressure holding the pin firmly against the case rim.So I trimmed the pin so that it had zero positive potrusion but now it doesnt hit case rim hard enough. I now have a 2nd pin on the way so I can try again. My next step is to leave the pin long and to put a good radius on th bottom of the pin. HELP.

That did the trick. You must put a tiny radius onthe bottom of the firing pin tip.This is critical.