When the .40a was first released Horizon claimed it would sit right in the same bolt pattern as the .30, it wasn't long before guys who bought the .40a to replace a .30 said no way. The .40a is in the new style crank case with the cam in a cam chest rather than in the cover. The older .30 was about the same size as the older FA .40 and .45 and .50. Like the .40 on the left.