There's plenty that the .243 will do that the .250 Sav won't. The .250 Sav is a great cartridge in its own right, but it died off while the .243 has thrived for a reason. As a deer cartridge within the range limits of the .250 they are essentially the same. Get into longer ranges or into lightweight bullets at high speed for long range varminting, and the .250 is grossly outclassed. It doesn't have a large variety of bullets to choose from. It lacks powder capacity. The .243 can send a higher BC bullet of the same weight at least 100fps faster. Again, trivial at close range but the .243 adds 100yds or so to the effective range.