Marlin 336 rifles have two part firing pins. The two parts are the firing pin, front and firing pin. rear. There is an old style and a new style firing pin, front. The dividing line for which style firing pin, front a gun takes is the year of manufacture. Guns manufactured in 1984 and after take the new style firing pin, front. Those made in 1983 and before take the old style firing pin, front.

Footnotes / Sources:

Marlin Firearms Customer Service Department. “Customer Service Call.” Telephone interview. 17 June 2016.