Hello, Mongo. I don't own a 74' Sharps..but it seems to me, there is a small coil spring visiable under the firing pin striker assem. (the part the hammer hits). Your right, in that as soon as the hammer nose clears this piece, the pin will be retracted.
I DO own an Axtel (Riflesmith) Sharps in .40-70 2 1/2". After I purchased it, I spoke with Tom Axtel about this same concern..he replied,"it will do no harm whatsoever..that pin is retracted as soon as hammer nose clears."
The so-called 77" Sharps from Shilo, will break the pin if hammer is not half-cocked.