The TSX is an all copper bullet, no lead. Copper is lighter that lead, so the bullet will be longer than a 53 grain lead core bullet. The longer the bullet the faster the twist has to be to stabilize it. I really has nothing to do with weight, just how long it is. In other words a TSX bullet is longer than a convention lead core bullet, thus it takes a faster twist to stabilize it; even if they are the same weight. You can get by with a slower twist if you push it down the pipe quicker. A 1 - 12" twist will probably just stabilize the longer bullet if you push it as fast as you can, that is why JonnyC was advised to make it step out at near max velocities; good advice I may add.
JIO - Jonny; Barnes says to seat the TSX bullets .050" off the lands, I would go no closer.
Good Luck and Good Shooting