Guns have long been a man's world. But as growth in the firearm industry slows down, gunmakers are increasingly focusing on women to boost sales—and that bet is starting to pay off. The number of women in the U.S. who practiced target shooting at gun ranges jumped 60 percent, to 5.4 million, between 2001 and 2013, according to the National Shooting Sports Foundation (NSSF), an industry trade group. During that same time period, the number of female hunters rose 85 percent, to 3.3 million. The organization adds that more than 74 percent of its member retailers reported an increase in women customers from 2012 to 2013, the most recent data available.

A woman fires a gun at the Ultimate Defense Firing Range and Training Center in St Peters, Missouri last November. Jewel Samad | AFP | Getty Images

Firearms retailers estimate women made up 20 percent of their sales in 2013 (the most recent numbers available), up from 15 percent in 2010.

Read MoreGun accessory maker: 'Lazy' retail holds us back Women who own guns are also often big spenders, according to the NSSF. The average female gun owner spends $870 annually on firearm purchases and another $405 on accessories, such as sights, targets and gun cleaning products, the group says. "The women's market is a force in our industry, and manufacturers, retailers and shooting ranges are making changes to their products and services to satisfy women's tastes and needs," said Jim Curcuruto, NSSF's director of industry research and analysis, in a statement.

For gun manufacturers, the female market represents a new marketing challenge—specifically, finding exactly how to appeal to these customers. "A lot of women struggle with the way a firearm feels in their hands," said Angelina Giudice, a marketing professional for Smith & Wesson. "It's not about the kick. It's not about the color. It's not about being pink or bedazzled. It's about how it feels." Read MoreGun lovers leaving Smith & Wesson for dead? Women are the fastest growing market for Smith & Wesson, said Giudice. She noted that ten years ago the ratio of men to women customers was seven-to-one, and that today the ratio "has drastically shifted," but declined to cite specific figures.

