My current favourite real obsolete cartridge is the 9x57MM Mauser. .358 Winchester ballistics about 50 years before the .358 was invented. I have a svelte little German "guild gun" '98 sporter in that chambering. Sweet!
I just sold another fine gun, a hundred year old Sauer drilling in 16ga.x16ga. ( 65mm chambers - 2.5" ) over 8x57JR ( .318" dia) That one qualifies as twice as obsolete.
Unlike some others who have posted here, I just can't think of the 7x57 as obsolete, or the .303 British, or 7x64 Brenneke either. They are all used widely throughout the world, perhaps not in the USA though.
