The model 686 has an excellent reputation as an accurate gun, based on comments by owners at forums like this. I have two of them, the 2.5 inch you mentioned, as well as the longer 6 inch barrel gun.
I find that I can shoot more accurately at distance with the 6 inch gun, which I think is due to the longer sighting radius making it easier to aim, as well as the greater weight of the barrel keeping the gun steady. But the 2.5 inch gun does well in accuracy, given the limitations of the short sighting radius.