IMO the accuracy is fine. I mean, we use flintlocks in NW and they are waaay more accurate IRL.
Just look at this guy. He hits the target every time with no problem.
Spoiler
[youtube]http://www.youtube.com/watch?v=wz56I4n9O4U[/youtube]
And that's even a carbine.
Now, the earlier muskets were less accurate than the flintlocks and that's why I think the current ingame accuracy is bad enough.
But I don't know, I think the Swedes actually used flintlocks during this time anyways. The Swedes started using it at the start of the 17th century (1600).
I think misfires should be implemented tho. But it would be pretty rare.