Shares of Smith & Wesson Holding (SWHC) and Sturm Ruger (RGR), the nation's top two gun sellers, fell for a second straight session amid renewed calls from gun control advocates for tougher laws after the killings of 20 children and six adults at a school in Newtown, Conn. Sen. Diane Feinstein, D.-Calif., Gov. Andrew Cuomo, D-N.Y., and New York Mayor Michael Bloomberg were among the voices calling for action. Feinstein said on a Sunday morning