This comes up every so often. Usually it's the cowboy putting too much of his finger into the trigger guard. This causes the pistol to move left when the trigger is pulled.
Try this: Shot the pistol 6 shots right and then 6 shots left (remember, Rugers are safe with all six holes filled). Do this one handed, two handed and on a sandbag if you can. If it is truly a sight alinement problem the gun should print pretty close left vs. right. One haned will probably have a bigger pattern but you're looking at the left vs. right placement of the bullets on the target.
If the results show a difference then try to put just the pad of your index finger on the trigger. That plus practice will help you keep your sight alinement as you pull the trigger.
If, however, left and right print at the same spot on the target you do indeed have an problem with your sights. You have a number of options:
1. Learn to aim just to the righ of where you want to hit (Kentucky windage)
2. Rotate the barrel to the LEFT. This moves the front sight left which moves the bullet strike to the right. Ruger barrels are a bear to tighten, though and there is the problem of "how much?" to move it.
3. Open the rear notch on its right side. When you center the front sight in the new wider opening you effectly have "adjusted" a fixed sight gun. There is the problem with how much and once it's gone (the metal) it's mighty hard to up it back. File a little and shot to see results, repeat as needed. Don't deepen the slot if you can keep from doing so.
4. Depending on it's age send it back to Ruger. They are very good (and fairly quick) about adjusting and returning it. 'Course it's going to cost for shipping and if you have any aftermarket parts they won't be coming back with the gun. Ruger has a policy of returning the gun to factory specs. If you do go this route take out all the springs and hammers/triggers/sears that aren't orginial.
I had this problem when I started out and have found that with a bit of thinking just before the timer goes off, and with a lot of dry firing, I pretty much hit what I'm aiming at.
As they say: You pays your money and makes your choice...
Good luck and let us know what you decided or if you have anymore questions.
ÇR