The Larimer County Sheriff's Office says officers were called to Rocky Mountain Shooter Supply near Interstate 25 at about 2 p.m. Saturday.
The Denver Post reports the man, whose name has not been released, was shot in the arm and taken to a hospital with non-life-threatening injuries. No other injuries were reported.
It was not immediately clear how and who fired the gun.
(Copyright 2012 by The Associated Press. All Rights Reserved.)