I did a quick search, and didn't find any reference that a 270-40 Krag, has been done. That is not saying it hasn't, or couldn't. I'm sure reamers could be made, no problem. Chambering this in a Contender, is however a questionable project. I don't see any of the usual custom barrel (TC) makers listing the 30-40 in the Contender. I'm thinking that the 40 case is quite capable of handling more pressure than the Contender will handle. Here lies the liability possibilities. A safer bet in the Contender, would be a 7-30waters AI. I think the 6.5 and 7mm BRM's, can be chambered in the Contender also.
Onesonek