given a repeatable sight picture and doing things the same way time and again, yes. They can be accurate.
For me, shooting in the low to mid 90's with an occasional 10x, at 35 yds is accurate for me with a .50 and a mild load. The trigger and your grip has a lot to do with it, that and lots of trigger time!
That Ruger old army at the top of this thread...well, they dont get much better than that out of the box!
of course, it comes down to what you consider accurate!
(I know of some folks who are thrilled to no end to just hit the target! all 18x18 inches of it!)
front stuffer single shots, production made...the Lyman and the traditions trapper are fairly good guns!