When you use the amount of tranqs it says, it will not knock out immediately. It will take some time for the torpor to catch up and knock it out. Took about 10 mins after shooting the right amount of tranqs for it to lock out. If you notice it's trying to run go up to it and check with a magnifying glass.
I dare you to raise one!! They are savage if you got two high lvl parents (about lvl 140ish) and you get imprinting on it. The thing will become an adult with about 230% melee and basically one chomp any bronto!!! But on the down side you loose your job and your girlfriend
Make 4 metal dino gates and 1 large bear trap. Place three frames and door into an incomplete square and the large bear trap in the I between them. Lure the Giga into the trap and while its trapped place 4th down to make the square. Then just light it up with tranqs