A few weeks ago I posted an inquiry about why S&W switched to internal firing pins and whether that required a heavier action to ignite the round. There were differing opinions (of course) about the action weight. Today I talked to a pistolsmith at S&W. He confirmed that the spring had to be about 25% heavier with an internal pin. This is because there is a spring on the pin whose tension must be overcome. The reason for eliminating the hammer pin was to simplify production (cut costs), but he said that the internal pins are more durable.
So there you have it.
So there you have it.