I just looked that shyt up and that's false.
Yes there are incidents where a leopard will kill a gorilla but you made it sound like they are a natural predator of silverbacks which is false.
"It may surprise you to learn that gorillas don’t really have any predators to worry about on a regular basis. However, there are times when they have problems with other gorillas or even various types of wild cats."
"Generally the wild cats know that they aren’t going to be a match for the strength of the gorillas. Still, that wont’ stop them from snatching a young one that has wondered too far from its mother or one that is too sick to fight. Leopards seem to be very bold when it comes to trying to get a meal that consists of a young gorilla."
"Amazingly enough, gorillas will use weapons that they make against predators. They can sharpen sticks with their teeth and they will use them to fight with. They are also known to throw heavy rocks at predators in an attempt to get them to run away. These abilities are very interesting to researchers as this is part of their learned behaviors and certainly not the result of the instinct to survive."
You underestimate the silverback.