With all due respect to One Eyed's comment, I suggest numerical analysis on a per-hour basis to see if a store is even viable.
- What is the fully burdened cost of staffing the store per hour, on average? (wages, SS, workman's comp, etc.)
- What is the hourly cost of rent, heat, insurance, taxes, etc
- What is your average weighted margin (average % margin on a per $ sold basis)
- Hourly cost of inventory. You should use a cap rate of at least 5% (probably a lot more) when calculating the opportunity cost of having $$ tied up in inventory
- Opportunity cost of what you would have earned on interest on the money spent on the shop build out (use the loan rate if that is borrowed money, or 0% if you borrowed it from a relative you have no intention of repaying)
- What is the hourly cost of shoplifting?
Now, you take two numbers:
- Hourly cost to keep store open
- Margin percent
And use these values to calculate the average per-hour sales you need to cover just the above listed basics. Note that expense is non-inclusive and omits legal fees; junk inventory (the stuff you can never sell - every shop has a bunch of this); liability insurance (you sell a gun that gets in a high profile shooting and it's going to cost you)
If you determine it takes $50 per hour to keep the store open and you average margin in 20%, you need to average $250 in sales per hour to cover that (actually more when you consider the other stuff). When you look at the deli emporium you can see sales in the thousands per hour, so it is easy to understand how they crack their financial nut.
If you envision a day at the shop as selling a gun or two, maybe a transfer, and a $100 worth of accessories you'll find there is a viability issue. On the other hand, if you realistically think you will get the kind of traffic to cover the hourly cost of keeping the store open and accomplish something other than working the shop for minimum wage (or less - there is no "owners minimum wage"), go for it.
And remember, there is one easy to make a small fortune running a gun shop - start with a large on (fortune, not shop).