Hi,
This works thanks to my package:
====
\documentclass[10pt]{article}
\usepackage[dot]{dashundergaps}
\begin{document}
\begin{tabular}{lll}
\hline
Head A & Head B & Head C\\
\multicolumn{2}{l}{\dotuline{\hfill}}\\
Col 1 & Col 2 & Col 3\\
Col 1 & Col 2 & Col 3\\
Col 1 & Col 2 & Col 3\\
\end{tabular}
\end{document}
====
HTH.