T-rex are not good that they can spot you easily. Weak spot for them is around their eye.

Here are the tips for hunting them:

1. T-rex sometimes stands up high looking for you, it roars like the sound of a Ceratosaurus if it spots you.

2. When it is far, use a sniper, but when it is running towards you, use a shotgun (I recommend a double barrel shotgun)

3. Look at your radar, relocate to the sea or lake where the T-rex is on shore and call it, then it will swim to you, then shotgun of any kind will work.(Doing this on RAVAREN'S BRIDGE is much easier.)