I can't say I own one of these, but I had STRONGLY considered buying one a year or more ago. In my research (which led me to not buying a '63 Pocket) I found that you need a large diameter ball, something over .315" in diameter. As the previous poster said, the chambers are horribly small, which doesn't help if you use the loading lever on the gun and are trying to shove a .319" ball into a .310 chamber. (>_<)
One positive I will say is I would have no fear of shooting this with 4F powder and that finer grain will up the velocity. Were this an original '63, I wouldn't put it in the same room as 4F powder.
What eventually turned me off the .31 caliber is the .36 caliber is much better and there are spare 12 inch barrels available for 1851 Navy revolvers. There are no easily obtainable longer barrels for the .31 caliber, be them in the 1849 or 1863 pocket revolvers.
The longer barrel is cool as combined with a stock it would make a cool rifle or I could just leave the long barrel on and pretend I'm Jack Nicholson shooting down the Batwing.