Sounds like a great price to me. I have a fiend that has taken many deer with one of these and he swears by it. If the price is the same, I would go with fffg of the 777. You will see a lot of listings for the use of fffg up to and including .50 cal. As stated, you would not use a patch with the sabot but you might want to put a bore button between the sabot and the 777. As far as mounting a scope, no problem and you might want to stay with a Shotgun/ML scope.
Be Safe !!!