Don't flame me, I'm just repeating what I read.... In Clay Harvey's book "Rifle Cartridges", he complains about the .257's lack of accuracy. I know a dozen people will chime in about their .257 shooting one holes groups all day long, and your's may. I just think it's an interesting read.
Who, pray tell, is Clay Harvey?? It puzzles me how a cartridge case that gives the kind of accuracy one gets from the 6mm Rem., the 6.5X57mm Mauser, the 7X57mm Mauser, the 8X57mm Mauser, and all the larger bore 57mm's suddenly becomes inaccurate when it is necked to fire .257" bullets! I would blame bullet quality for poor accuracy before I came to the conclusion that something about the case shape, or even less likely, bullet diameter, is to blame....