I just picked up a Ruger American Predator in 22-250. It, too, has the medium diameter threaded barrel. This one has been on my "as soon as convenient" list since it was introduced. A seller had one listed at $7 over wholesale so I took it home.
The first shots happened this weekend. It is a dandy little plinker. It's awesome for a cheap gun and will hold it's own against much higher priced rifles. In fact, it turned in groups well under an inch with some random 69 grain loads I rolled out.
As for the bolt being gritty, if your Rimfire is anything like my Predator the "grit" you are feeling is likely the machining on the bolt. Those bolts are clearly lathe turned and the finish, while nice, is not the mirror polish everyone wants. That is one way they keep the cost down.
As a machinist, I can appreciate the finish and understand why it is what it is. They get a thumbs up from me.
It will make a bit of a light zipping sound when you slide it back and forth. I don't mind that at all. It's actually kinda functional, especially in a caliber as dirty as a 22. The gunge can collect between the tiny grooves and not affect the action. Think of it like tread on a tire.
Enjoy your new shooter. I certainly enjoy mine.