Firearms and Ammunition stores are very common in many parts of the United States (notably less common in most other countries), especially in the South, the Midwest, and more mountainous or forrested states. During a zombie emergency, these resources will be heavily sought after. Depending many factors, this could provide a survivor troupe with the guns they will need to survive, or a sudden stop into a virtual deathtrap (of zombie or human adversaries). As with many buildings, it's usability as a long-term fortification may vary wildly. Generally speaking, retail storefronts of all types tend to be very low rated for the sort of structural integrity and command viewpoint needed to hole up against the zombie plague. It is worth mentioning that gun stores, frequently built and owned by persons of a more survival minded mindset, may be reinforced or oversupplied in ways that the common shopkeeper would strike many as financially excessive before the breakdown of order.
A visit to a firearms store would not only have to contend with the swarms of infected/undead, but also the considerably more challenging horde of desparate people wanting access to their supplies (or the owner holing up to defend their cache). Likewise, the constant commotion would likely make the whole area a denser hunting and breeding ground for zombies. All in all, a trip to a gun store at many phases of the outbreak are very high on both risk and reward. Options should be weighed carefully on a case by case basis, and advance info, or scouting of the area may be crucial. If at all possible, procurement of a a secret personal stockpile of both guns, ammo, and other tools and accessories before/in case of a zombie outbreak is the best option.
Plentiful supply of weapons and ammunition. If one has access/permission to use it, it can be a great resource for a safezone. If the situation permits gun stores may be used to produce homemade weapons and ammunition to be distributed.
They do not contain much food beyond vending machines and whatever is left in a possible employee fridge. They typically are not built well as a defensable location and should be looted rather than used as refuge, unless you are in Tennessee where it is the law that all privately owned gun shops must have permanant bars placed over their windows and doors. Check your local laws for the security requirements of local gun stores. Also looters would try to get in there.
Lastly, if already in use as a base, it is a very difficult building to assault, break into, or persuade one's own entry, as its occupants will likely have already seen the worst in humanity before your arrival, and will be extra defensive. Or they will barricade themselves on the roof with a hunting rifle, some binoculars, and a large amount of ammo to play a game of whack a looter.