I think the problem with a TTSX design in anything over 250 is that they would be so long that the case capacity would be affected so you wouldn't gain anything ballistically. I could be wrong but it appears the design is better suited to the lighter bullets like 165's in 308 and 130's in 277.
BTW I really tried but couldn't get decent accuracy from the 250TTSX in my M70. Hope you have better luck.

I am continually astounded at how quickly people make up their minds on little evidence or none at all.
Jack O'Connor