Gun ownership has been in decline for decades (along with hunting). In response, the industry shifted from hunting and home defense toward civilianized combat weaponry like the AR-15. There's a large accessory and customization market for these things. It's essentially a toy for military hobbyists and gadget-lovers.

More info: http://www.nytimes.com/2013/02/03/business/the-ar-15-the-mos...