Hello the fire
I live in Ruger Country, the next town over from the manufacturing plant in Newport, New Hampshire and know a number of folks that work there. That said, before I knew about it I had bought a new Ruger a number of years ago and when I got home and did some cleaning, I thought it was a used gun due to the residue. I went back to the dealer and found out two things; 1) Ruger test fires every firearm and 2) they don't always do a cleaning.
Part of this was from the requrement from some states to have a fired case come with the firearm as part of the "case ID shows which firearm it was fired in" and to just make the sure the firearm is operational out of the box. I wasn't sure if they used jacketed bullets or lead but the pictures show the streak of copper I have seen in the past. This is Ruger's way of making sure the firearm works and to comply with som of the quirky states.
Chelsea