Mkk1 and ronnie are absolutely correct.
The hammer mounted firing pin (S&W calls it a hammer nose) is attached by a rivet and pivots by design. Some models actually have a small spring behind the hammer nose that controls the positioning. The bushing that the firing pin passes thru (hammer nose bushing) is stationary and closely sized to prevent primer flow and escaping gas in case of a pierced primer. Since the hammer swings an arc, the hammer nose needs to pivot so it can pass thru the bushing. I purchased a M1917 cheap at auction because the hammer nose was locked up with dried grease, which effectively seized the action. A little cleaning and it worked perfectly!

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