Smith & Wesson Holding Corp., the Springfield gun maker, surprised Wall Street with a very strong quarter. Sales surged last year after the massacre in Newtown, Conn., and other shootings. Many gun enthusiasts went on a buying spree, fearing restrictions on ownership. Net sales were $145.9 million, up 7.1 percent from a year earlier. The company raised its fiscal 2014 guidance. It estimates net sales of $615 million to $620 million and earnings per diluted share from continuing operations of $1.39 to $1.42, better than analysts forecast.