That’s, quite simply, incorrect. The range of an average sharpshooter is 600-1200m. And I’m an elite sharpshooter. However, sure, let’s say I’m average. A t-rex could run at 45 miles per hour. This is roughly twenty meters per second. So, at the absolute bare minimum, it would take a t-rex 30 seconds to even get close to me. And that assumes it could find me, first. However, I have the best silencer that money can buy, as well.
Here’s a quote: “One of T. rex’s unique abilities was its hypersensitive hearing. A bone in its inner ear, the cochlea, was remarkably long. And in animals alive today, that specialization is associated with the ability to hear low frequency sounds well.” It doesn’t matter if it can hear low-frequency sounds, as a gunshot is not a low-frequency sound, even at the very, very low chance it could hear it, while it has been suppressed, from anywhere between two fifths of a mile to multiple miles away. Again, it will take them at least 30 seconds to get near me, and even then, I could just… retreat to further away. Furthermore, t. rexes are much larger than humans, so I could really move even further away whilst still being accurate enough to kill. I don’t even need to kill with the first bullet. I could just wound, or I could even just miss and shoot again. If a t-rex even attempts to follow me through the portal - first off, it’s incredibly unlikely that it could even fit. However, even if it could that would still work to my advantage as, due to their size and body mass concentration, they would not be able to move through very quickly. So, I could easily just wait until they were halfway through, fire a new portal of the same color, and woops! That t-rex just got fucking chopped in half!