My Mini 14 Stainless Steel (prefix 584) has a very rough finish. I watched the Ruger factory video series on You-Tube and there you see the workers tumbling and "polishing" the receivers. Frankly, my receiver looks like they skipped/forgot those steps.
No issues with mine .(583 series.) If you contact Ruger CS and explain that you aren't happy with the finish, they will more than likely ask you to send it to them and they will fix it up for you. They have great customer service.