Before I can answer the question I first must ask some questions of my own:
How many guns might my potential enemies have?
How powerful are their guns likely to be?
How much ammo might they have?
My answer will be, then, "more than them."
A drill sergeant asks a recruit, "What would you do if I suddenly appeared at the top of that sand dune with a tank?"
The recruit responded, "Why, Drill Sergeant, I would blast the tank to smithereens using the big guns on my battleship!"
"Battleship?", said the drill sergeant. "Where in the world would you get a battleship?"
"The same place you got the tank, Drill Sergeant!"
The moral of the story, of course, is that there is no consideration of fighting "fair". The object is to have sufficient force available to annihilate your enemy with little or no risk to yourself.
If somebody is standing in front of your car about to shoot you with a pistol, do you grab your rifle and jump out of the car firing? Or do simply jam your foot on the gas pedal and run them down with your 3000 pound vehicle?