The smallest I have seen in orders to makers, is 180 balls to the pound. The gauge of 180 to the pound is .296". I'd think that gun might shoot a 200 to 210 to the pound, ball - approximately 33gr. weight(at 210)- the same weight as one of the newer 'hyper' velcoity .22's, some 7gr. lighter than a .22 LR. The ball would be around .285". These are guesstimates - as my downloaded chart (The Los Angeles Silhouette Club) only indicates from 1 ball to the pound at 1.671" & 7,000gr., to .296" at 38.9gr. the is is the most accurate chart I've seen. The chart in Ned's book is incorrect with the balls I checked.
The buck-shot Taylor purchased for his .25 Rayle barrel, weigh 22gr. ea. That is a current weight for .17 calibre bullets used in handloads for CF rifles.