Push doubling: Push doubling occurs when a die bounces off the surface of the coin, shifts position, and lands lightly in a different spot. A diagnostic feature is marginal shelving at the edges of design elements. Interior features often show rounded doubling that is easily mistaken for the effects of a double strike or a doubled die. Push doubling can occur on either face, although its most dramatic expressions tend to appear on the face struck by the hammer die. Cases of push doubling can involve up to three closely-spaced sets of accessory design elements. Push doubling can occur on both faces simultaneously and often in different directions. Up to three different doubling directions can be represented on a single face. http://www.error-ref.com/machine-doubling/
