Today I stopped by a small sporting goods store that has been around since, according to the wife of the owner, 1946. I remember going there as a youth for fishing supplies, and with my father and older brother for firearm-related items back in the 1980s. My reason for visiting was largely nostalgia, and also for .44 Special ammo, but I mainly wanted to see the old place. Anyway, whilst there, I spied not one, but two boxes of .307 Winchester ammunition on the shelf. No, that isn't a type-o, such a cartridge exists. I believe it is still factory loaded, but it never caught on. I've read online that it is popular in Spain because it has .308-like ballistics, but isn't a "military caliber", which is prohibito in that country. During the drive down the 101 I was thinking of various failed cartridges in the modern era. There are certainly old cartridges, good and bad, that have faded away, but I'm thinking of relatively modern (post-war) introductions. I can think of a number, but I thought I'd toss it out there for discussion: what "new" cartridges do you recall making a splash and then going away? Were they good, bad, or meh? Why do you think they failed?