You're talking about the Sloth legendary sniper there, and the whole point of that gun is that it trades bullet speed for additional damage--slow bullets is not a general characteristic of Dahl sniper rifles!
Personally, I don't like the Dahl Sloth. My preference has always been the Jakobs Penetrator.
Steam username is Triscuitable.
I got VAC banned in COD: Ghosts for using an FOV changer.
I try not to think of how sad that is.