Hello ... I got the double rifle in hand today. Its in spectacular condition. But, now I'm really confused as to the caliber. I guess the "CAL 3 24" marking must stand for 3" 24 gauge ? But the chamber cast is identical to 600 NE, except with a thinner and smaller dia rim. Perhaps a 600 bpe?

any suggestions?

https://www.buckstix.com/buckpics/24ga-cast-000.jpg