One question I have is the age of the rifle. Ruger started making their own barrels around 1990 and they are pretty good. They also started using shorter throats on their chambers, which also helped things.
In general I have had very good luck in getting post-1990 No. 1's to shoot pretty much out of the box. The one modification I do try on these rifles if they don't shoot as well as I'd like is to epoxy-bed the very tip of the forend, the last inch or so. This stabilizes the forend, which may be your problem. It's a very easy thing to try.
So far all the post-1990 No. 1's I've owned (maybe 8 or so) have either shot well out of the box, with the forend screw tight, or responded very well to tip-bedding. I haven't had to try any of the usual array of other No. 1 tricks on any of them.
