Joe thanks for the unique images. I remember volunteering to work on Canadian National 4-8-2 6060 in Jasper, Canada, and they put me to work with the needle gun for 2-3 days. My body was still vibrating an hour after I was done.
It was a crummy job but good experience and saved a more experienced worker to do something more important like make boiler lagging or other things. Now when someone mentions a needle scaler, or needle gun I can relate!
Greg