Ha ha good try. Actually some of the early American metallic cartridges had their names plagiarized by rifle manufacturers such as Remington, Marlin, Winchester etc, only because of specific loadings they produced for their particular rifles e.g. exactly same cartridge as originally named Winchester only called Marlin because of lighter or heavier bullet or loading used for the marlin rifle.
Cartridge nomenclature can be very messy.

I note you are sizing .257 calibre bullets to .254 for your Mauser .242. My brother used a 250-3000 for many years and found the Hornady 117gr round nose bullet the very best from cup and cores for game, such as feral goats, chamois and right on up to big red deer. The 117gr bettered the 100gr bullet by a good margin. Could be worth trying in your .242 Mauser and even your newly acquired double although regulation maybe a problem with the double which I imagine was done with 100gr bullets.

Will be interested to know how your double shoots so keep us informed.