Some indoor ranges have rules about only shooting bullets with no exposed lead. To accommodate cast bullets, companies like Rainier plate their bullets with copper. This approach is still cheaper than even the least expensive major bullet makers jacketed bullet (Winchester or Remington bulk jacketed bullets). Gas check will not pass the above rule.
The reason is to minimize lead dust in the shooting range inside a building. They usually have large fans to push the air away from the shooters, through lead filters and out of the building. Lead is a hazardous material in some states like California and enclosing the bullets in copper keeps the lead dust to a minimum. This is not a new rule! I use to shoot in an indoor range some 15+ years ago before I retired and moved to the High Desert and they had that rule back then. I used Rainier bullets even back then.
LDBennett