My experience when I owned my gunstore was as the other posters described. Gun sales alone will not make it. Accessories, trades and gunsmithing provide the real income.
A single dealer often cannot match high volume stores. The K-Mart near me could sell H&R guns for 20% less than I could buy them for direct or through a distributor.
To compete I provided service and tried to focus on better guns than K-Mart would handle.