.257 Roberts (usually referred to in this version as .257 Plus P) is considered a long action, some list the round as long action! So be advised for .257 Roberts be sure to check out the EXACT cartridge and length of action! I have never put the wrong cartridge in a rifle chamber in any other caliber. But .257 Roberts I did load in a .243 from a cartridge belt in the field! Luckily BOTH rounds I mistakenly chambered in a .243 (Winchester Model 70 Ultimate Shadow SS) jammed in the chamber and the bolt had to be next day placed on a deck, pointed in the safe direction and lightly tapped with a rubber mallet and the WRONG round safely ejected! Make SURE you carry rounds in a cartridge belt for only what you are shooting on that trip!
LONG answer but having handled many weapons under many conditions such diligence is required! AGAIN the .257 Roberts is to me one of the best rounds for light to medium game. The 7X57 Mauser was very similar.
You can read a great chapter on the .7X57 in Jack O'Connor's book
The Hunting Rifle in the chapter titled "Great Round in a Little Case" Jack sold all his reloading dies for 7X57 and felt the .257 Roberts was the best round available when he wrote the HuntinG Rifle book. He also sadly stated the .257 was going down the drain but recently quite a few manufactures produced .257 such as Winchester Model 70s in both the Featherweight and the Cabel's .257 Roberts Anniversary Featherweight Deluxe.
