The 168 grain TTSX was stiffened up so as to not loose its pedals when impacting at close range from the big 300 Mags ( Rum & 30/378) as a result the minimum impact velocity for expansion is 2000 FPS per Barnes. The regular TSX is 1800 FPS and I have taken game with the 180 TSX out to 777 yards
If you don't believe me call Barnes and ask the minimum velocity for expansion for the TTSX 168 grain. The TTSX minimum velocity for expansion is not the same in every caliber, case in point the 225 TTSX 338 cal bullet has a lower minimum impact velocity than the standard TSX.
One must pick projectiles for Long Range Hunting carefully. I have used the 180 TSX in my 300 Win for a number of years and would never switch from it to the 168 grain TTSX since it would reduce my range
The standard TSX needs no help in opening as this high speed photo shows. The TSX is completely opened in 2" of ballistic gelatin
range it,check the wind, dial in correction, aim and only one shot