I have always had a lot problem with my snake taking rats and i finally just gave up on it. A lot of people have different people have different opinions on what to feed how much and when. Given that BP's can be know for being picky eaters you really just have to find what works best for your particular snake.
For me, my snake wants nothing to do with rats of any kind what so ever. So at this point i feed her 4 mice every 2 weeks. If your snake will take rats more power to ya man, i wish mine would cause it would be a lot easier for me, but she is a stubborn and knows what she likes!