I've got a way to smooth it up, and it works with almost any firearm that's got an accessible hammer... but it's got to be done with EXTREME CARE with the SU!!!
Open the action and ensure the hammer is cocked. Now, BLOCK the hammer with something... your thumb, preferably, in a tough gardening glove.
What you're going to do is push forwards on the hammer HARD, then pull the trigger (which will be HARD to do). Doing this a dozen times is roughly the equivalent of three or four hundred firings and "marries" the sear and hammer step together.
HOWEVER, make SURE the hammer doesn't slip past your thumb and dry-fire against the gun itself. You're gonna be looking at a trip back to the factory almost certainly!
Done carefully, though, this little trick works wonders (I did it on mine long before it ever saw a range).