Looks like a Heym Express but I have been wrong numerous times before. Also the story mentions the .416 Rigby owing its popularity to Ruark's writing. This has always seemed a little surprising as it really doesn't get mentioned a lot. In Horn of the hunter Selby only uses it for back up on lions and is quoted as saying that that is all it can hit. He also shot some Hyenas that were becoming a nuisance. Ruark describes it as a dirty rusty looking 416 yet is credited with its popularity.