I had two customers develope loads in rifles I built for them this summer chambered in the 257 STW using the 115 gr TSX.
I tried the standard X bullets and even the XLC bullets and never did like them because they just were not as consistant in accuracy as I wanted and seating depth was so critical.
From the groups my customers have sent me using the new TSX, this does not seem to be the case. They still should be seated at least 0.030" off the rifling but in those two rifles they were producing sub 1/2 moa groups consistantly and at +3600 fps as well.
One of the rifles shot them very well cutting 1/4 moa groups quite often. Course both these Lilja barreled rifles were total custom rifles
built on accurized Rem 700 receivers and shot every bullet from the 100 gr Ballistic Tip up to the 130 gr Wildcat BCFBHP into 1/2 mao class groups.
I will say that they do seem to be much less finicky compared to the standard X bullets and velocity is more inline with conventional bullets of similiar weight.
Try a box and see, thats really the only way to know. Personally, I prefer a leaded bullet over any solid designed bullet, but that is my personal preference only.