A delivery wire assembly for delivery of an occlusive device to a location in a patient's vasculature, the assembly having a distal end portion comprising a proximal rigid segment, a distal rigid segment, and a flexible segment disposed between the proximal and distal rigid segments. The assembly also has a delivery wire conduit having a proximal tubular portion coupled to a distal coil portion, the respective tubular and coil portions defining a conduit lumen. A plug is seated in the conduit lumen and secured to an interior surface of the delivery wire conduit. A core wire is disposed in the conduit lumen and having a distal end extending through the plug, so that the plug secures the core wire to the delivery wire conduit. The plug may form a substantially fluid tight seal of the conduit lumen.