What size ammunition would this derringer accept?

Question

http://www.kitterytradingpost.com/product.php/pid/103/sid/664/prodid/9632

I can't find any leadballs smaller than .315 diamater and it claims to be a .310 caliber pistol, would the .315 balls be to large?

also, what powder chare would it use? would 5 grains offffg be to much?

annyone have this or something similar that canhelp me? thnx!