That's still extremely small. He must have been severely underfed his whole life. I don't know how old my biggest bp is (I'd always assumed maybe 5, but he could be 15 for all I know) but even directly from the poor conditions I rescued him from he was fully grown and weighed at least 1600 grams. I didn't have a chance to weigh him for the first couple of months, so I can't tell for sure. At 766 grams your guy should be able to manage a small rat with no problem. There are some snakes that really do refuse rats and only eat mice, but I'd keep trying the rats. My youngest came to me from the breeder eating live small rats, but when I tried to feed her live she always ran from it. I ended up feeding her a live mouse, then switched to f/t small rats. She never strikes it, but will always eat it if I lay it in her tub. To me it almost seems like she's afraid of her food, I don't know why.