200 yards on moose or elk with a round ball gun is not out of the question, but as I noted above, there are some criteria must be met.
1st of all, the calibre and charge must be capable - secondly, so must the hunter/shooter.
We have proved this capability, accuracy wise, using my .69 rifle. All 10 shots in the kill zone of an elk or moose sized area.
5 shots offhand and 5 shots sitting with cross sticks.
So-saying it cannot be done is different than saying most people should not attempt it.
The hunter would need to practice at a variety of ranges out to 200yards and become proficient to that range.
Is it recommended, no, due to unforeseen problems - with range, lighting & with wind, the huge stickler. round balls blow a long ways, in a breeze.
Simply hitting a 16" x 14" target time after time at 200 meters (218yds) offhand is a regular occurrence, if you practice doing that.
At our long range, now, we have 50, 100 , 150, 200, 300, 385, 500 and 600 meter targets.
The first 4 listed are quite easy, with my rifle.
Would I purposely attempt such a shot on a moose or elk? No. I would get closer if possible. But, I could.