A clamp ring assembly for use in a can bottom forming assembly comprising a clamp ring retainer, a clamp ring having a biasing assembly and an inner dome die. The clamp ring floats with respect to the clamp ring retainer to accommodate off-center contact by the punch and to center the punch at the end of the ram stroke. A slightly conically shaped inner dome die structure or dome plug may be provided to further center the punch at the end of the ram stroke.