Daryl & 4str,
4str:
I know this thread has drifter a little off the original question, but since the whole premiss of using a .615 ball in a Ferguson is the starting point, I think the correct ball size for the Ferguson is part of the discussion.
Daryl:
You are correct, one group of each ball diameter at 25 yards does not constitute much of a test. A .615 ball sounded very undersized to me until I read through Bryan Brown's information (i.e. posts on ALR), which is quite extensive. I believe he and Ricky have more rounds through a Ferguson than anyone else I know of and have written a book about their experience to boot. (I don't know if it has been published as of yet.) To cover my bets I have molds for .615, .620, .630, and .650. When I get a chance to shoot it a lot more, I will sort out which ball size this particular rifle likes best, including not only accuracy but leading, loading ease, fouling, etc.
Thanks