The design of the M14 /M1A /M305/M14S features a an internal design that prevents the firing pin from going into battery in fired /extended position .In simple terms a slam fire with the firing pin jammed forward simply will not happen.
When the bolt cycles to the rear after charging or firing the rifle ,It resets the trigger and as the bolt moves back into battery the firing pin strikes the firing pin bridge safety this is located between the rear sight and the charger guide . This feature resets the firing pin to the rear and if the firing pin is damaged and siezed the bolt will not move forward in to battery.Unless this bridge has been altered or removed the firing pin will always reset to the rear .Remember that this is a Battle rifle and that they included this feature to prevent frozen or stuck firing pins from causing AD's
When the bolt cycles to the rear after charging or firing the rifle ,It resets the trigger and as the bolt moves back into battery the firing pin strikes the firing pin bridge safety this is located between the rear sight and the charger guide . This feature resets the firing pin to the rear and if the firing pin is damaged and siezed the bolt will not move forward in to battery.Unless this bridge has been altered or removed the firing pin will always reset to the rear .Remember that this is a Battle rifle and that they included this feature to prevent frozen or stuck firing pins from causing AD's