Since we're showing off our guns
here's my C-73599. That's the experimental type number progenitor to the 15GP22. Mine glowed pink in the neck around the gun when I fired up my '54 Westinghouse and when a HV vacuum leak tester is brought near the neck or sparked to the pins. I'd guess the vacuum has deteriorated to probably 50 microns Hg or maybe worse. That's the kind of vacuum you can pull with a single stage mechanical roughing pump.