Why kill them, just drive them away, that is a lot easier.
To drive off an animal anything that causes significant pain will work for most, except for the rare berserker animal like wolverines and boar. Humans drive off lions just by chucking rocks, so even small arms fire will drive off most dinosaurs. Pain equals "screw this there are easier thing to eat" for most animals it works even better if they associate the pain with the area and not the animal (basically all projectile weapons) becasue then they aviod the area entirely.
If you have to kill them, then a bullet to the brain or heart kills any of them assuming you can hit it.
A decent pellet gun will penetrate the skull of Archaeopteryx just as it will a chicken. Basically you can just use another animal of the same mass for a rough comparison. The only ones that will give you any trouble are the ceratopsians (which you don't have to worry about) and the largest sauropods.
Sauropods have tiny heads, so comparing them to a giraffe or horse head is fine. Other difficulties is how small and well buried the brain is in the dinosaurs, it's not like mammals where the brain is a significant portion of the head. Heart shots might be possible except your sailors are not going to have any idea where the heart is until they kill and dissect a few.
Theropods From a campfire discussion among bored paleontologists the best way to deal with a T-Rex was automatic fire at the knees followed by a RPG to the head. The knees are a vulnerable point on any biped and lung shots don't work well on things that are breathing with air sacs, body shots are not that effective for a quick kill on theropods. As for the RPG there is a lot of tissue and bone around the brain on the large theropods, an Allosaurus or Dilophosaurus won't be anywhere near as bad although you will still have to put a lot of rounds in the head to hit the brain especially from the front. I feel I should point out Dilophosaurus and Allosaurus did not live at the same time. Of course once you put them on the ground by taking out the knees, they are not much of threat either.
Your biggest problem is that you need to flank them to kill them, from the front hitting the heart or the brain is all but impossible. Best bet is to shoot the knees on the bipeds, then dispatch them at your leisure. Also worth considering, Allosaurs are known pack hunters.
Oh, I should mention there are a lot of crocodiles around at the time, some as big as modern crocs that attack humans, some long legged terrestrial running crocodiles existed as well. Something else worth considering is herbivores are often far more dangerous than carnivores, carnivores tend to be wary of something they have never seen before, while herbivores will attack because you are something they have never seen before. In both cases strange = potentially dangerous.
Stegosaurus is a defensive fighter, so just stay away from it. They can pivot very quickly and the tail is a nasty weapon. What most people do not realize: Stegosaurus is fairly well armored so you are going to have a hard time killing one.
Brachiosaurus is tricky, shooting the head will require good marksmanship, and shear mass will provide a lot of defense. Your best bet is to go for a series of low gut shots and let it bleed out. You can shoot at the legs but moving legs can be hard to hit which means getting closer than is probably safe, keep in bind the leg bones are bigger than a person so you are going to need a rifle to do any rea damage.
Other animals to consider at the time include Amphicoelias one of the largest sauropods to ever exist, Gargoyleosaurus and Mymoorapelta two heavily armored ankylosaurids
More dinosaurs from the morrison formation: