I had that issue with a new to me Mk III bull barrel model. I didn't notice the looseness when I bought it. I called Ruger and explained the issue, and they e mailed me a shipping label. I packaged it up, sent it in and in three weeks it was returned with the frame/grip tight and as good as new. They also went through it and replaced the hammer spring as well... all for free.
This dedication to customer care may be why I have more Ruger firearms in my safe than any other brand...