Pre Tek suit, the easiest method is using a Managrmr. Just walk backwards and spam your breath until it roars. Then run up to it, jump off the mana, and feed it biotoxin. Manas speed, range, and freezing ability makes it super easy. You can escape quick if you miss a feed and the low breath damage makes it easy to see when the acro is getting too low so you don't accidentally kill it too.

More Acrocanthosaurus Taming & KO Tips