That depends on the distance and the manner of loading.
Smoothbore muskets are inaccurate, aren't they? Hence the need for 18th century armies to fire big volleys in order to get any hits.
A part of this is that the manner of loading, particularly under the stress of combat, causes variation in the powder charge. The amount of fouling increases as more shots are taken. The loose-fitting ball bounces up the barrel and will leave on slightly-varying trajectories. Hitting a man-sized target at 50 yards is difficul.
But, if you take such a musket to a modern meeting (e.g.
https://www.mlagb.com/) and load it carefully with a patched ball and well-measured charge, under relaxed conditions, with the bore swabbed for a consistent amount of fouling, then they become sufficiently accurate for tight (a few inches) groups at 50 yards.
Pistols are much the same; loaded carefully, as I assume would happen before a duel, and they are very accurate. Of course, if the seconds were sloppy and used an undersized unpatched ball, and the distance was more than 10 paces, I'd expect inaccuracy.
Some rascals had their pistols rifled until within an inch or two of the muzzle so it wouldn't be noticed on a casual inspection.