Time for a reality check. Competitive mark up for most firearms is less than ten percent. You will NOT make any money trying to mark firearms up higher than that, because regardless of how 'crummy' the other guys are, your customers will go to the ends of the earth to save a few lousy bucks.
The idea of having a shooting range though MIGHT just be the way to go. Clean, well lit, have an RO (yourself - if you aren't trained, you can get training) on site at all times.
Sell guns as an aside. The firearms business is VERY COMPETITIVE. VERY.
Go to the business closest to you that sells firearms. Have a LONG chat with the owner, if he/she can spare you the time, which is doubtful.
GOOD LUCK. Not saying it won't work, just saying that most firearms sellers go out of business in the first five years, as do resturantuers.
You want a good example of what you are talking about doing. This would be a great model for you to follow.