Cocking Piece
The part at the rear of the striker that the sear holds and that cocks the firing pin spring as the bolt is worked.
The cocking piece sits at the back of the striker assembly and is the surface the sear engages to hold the action cocked. As the bolt is lifted and run, a cam draws the cocking piece rearward and compresses the firing-pin spring, so that pulling the trigger releases the sear and lets the spring drive the striker forward.
Because the cocking piece is part of the moving striker mass, its weight and the spring behind it influence lock-time, the brief interval between sear release and primer strike. Smoothing and tuning this engagement is one way gunsmiths refine a clean, predictable trigger break.