You miss read my post. I wrote that the 257R is best at nothing. That means that while it's a good cartridge and functional like many others that it's not superior at any particular task.
The 243 is in the same group in a way. It's small for big game and good for pests and target shooting. The 257R never got off the ground because it came out before good bullets were available thus it was not all that accurate.
Around 1950 Sierra adopted the sizing up principle of bullet making which made all cartridges more accurate.
