Well, I have no idea how accruete they are, but with the right load and projectile they can both be reasonably accurate.
The first time that the Minié bullet was used in anger was during the Crimean War, and the main targets, Russian gunners, were mightily impressed to be slaughtered at 600 -800 yards by the enthusiastic British and French infantry.
I shoot a .58cal carbine, a two and three-band Enfield as well. Loads go from 45gr of 3Fg [50m] up to the service load of 2.5 drams - 68.5gr, depending on the range, of 3Fg - 2Fg also works well. I've never fired the three-band further than 600 yards though.
Groups from the carbine hover around three inches at 50m and six inches at a hundred - same for the two and three-band rifles, but it is imperative to have the correct-sized projectile. If you have a REAL Parker-Hale rifle, then it should have the correct mould along with it, else you are going ot have to do some figuring and experimentation. the correct size is 2thou less than bore diameter, and the lube is also fairly critical. On a good day you can figure on getting a group of around 12" at 200 yards, depending on your level of skill. They ARE all somewhat picky, so don't be expecting anything like a modern laser-like accurate shoot.
Watch Youtube - https://www.youtube.com/watch?v=UmflqQfgXgM
Rob there uses correct loads, even wears the correct uniform, and has a HUGE experience shooting these guns.
Another great site is capandball. The owner, Balasz Németh, is THE man. He and his brother run a huge BP gun store in Budapest, and he is a former world-class BP target rifle AND handgunner. He is also 'Mr Pedersoli' in Hungary, so much of his stuff is aimed at publicising their wares. No bad thing, really. But he DOES shoot a lot of the real thing, too. He recently had a difference of opinion with the folks who run YT, and needs support. IMO he is worth every forint.
OTOH, a visit to Wedgnock on a shooting day will bring dividends - nothing but BP shooters there.
tac
PS - some people shoot substitutes like Pyrodex RS. Do it if you must, but is IS different - feels different - and my loading figures do not count.