JJ,
I think the plastic tip TTSX was made to give more reliable opening. It seems that in some of the smaller calibers there were instances where claims of bullets acting like a solid and penciling through game were made. I have never experienced this but up until a few years ago, shot nothing smaller than 308cal.
It also significantly improved the BC going from the 235TSX to the 250TTSX in 375cal.
The TTSX's do not seem to offer any accuracy improvement over the excellent TSX, in fact I had some difficulty getting the 250TTSX to shoot well but have solved that problem.
