Dangerous. Leaves damaged walls, floors, furniture, etc. Not sure what to tell you to do if poison doesn't work. If I just had to shoot in the house, I'd use a pellet rifle. Put something outside that the rat would like more than the things you have inside ........... open the door .......... and wait .......................
You are going at it all wrong, rats and mice are critters of the edge. in other word they like the walls, rats have very poor eye sight so they use there whiskers to feel among the walls and edges. Poison is not good because they will die in your walls and smell like rotting garbage and you will never get the smell out. The best thing is good old fashion rat traps with some peanut butter. They can't carry it off and shooting will do nothing but damage the house.
Look for a hole or entry and remember rats can basically squeeze into places you would not imagine they could so set you traps along the wall away from other animals and wait. If you have rats they will be along soon and you will hear that trap breaking their neck and its more humane then poison which will kill more than the rats
I had a rat once and it was smart and kept avoiding the regular trap. I was to the point of keeping the old "barn cat" inside at night to have a go at it. I finally caught it in a live trap. I was carrying it to a large bin filled with water to drown the rat and tipped it and the end door opened up and the rat got out. The cat didn't see it and it ran behind a cabinet in the living room so I took the cat over to see it. The rat escaped through a hole in the floor where the TV coax comes up from the basement. Now that the cat saw it, he knew what I wanted. The next morning, the rat was laid out neatly on the steps in the living room with a hole chewed in the back of its neck. Moral of the story, if you don't mind having a cat around (even an outdoor cat that you bring in at night to do what they do best), GET A CAT.