My boa is about 2 now and is still on small rats. Like bcr said, if they prey item is bigger around than the snake, it's too big. You will need to find someone that can probe it for you (an experienced snake keeper or breeder). I think popping is harder on larger snakes and you are more likely to hurt the snake. It is almost certainly a Bci... Bccs are rarer and more expensive. Other than that, I don't have much to offer you.