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Man vs Dinosaur. It is a relatively common trope in various Sci fi settings, most famously done in Jurassic Park. These depictions have always fascinated me. I have always been bothered, however, by the way in which the guns the people use against the dinosaurs are generally shown to be of little use. Given the effectiveness of our modern weaponry, I feel like they would be significantly more effective than shown. Though, I have heard of animals such as Bears having some level of bullet resistance, and the Cape Buffalo even showing some ability to resist shots fired from massive "elephant guns." I would therefore imagine that it is possible for dinosaurs to have some level of resistance to gunfire, but I don't know enough about ballistics or Dino biology to properly answer the question of what the effects of modern weaponry would be on the giant (Reptiles? Early Birds? Something else entirely?).

I not looking for exclusively hard science, but science should be used to back up the answer. To narrow it down, let's look at two sets of three specifics. (Answers don't need to be limited to these options, but I think they provide a good overview.)

First, the firearms in question. What would a 9mm Pistol round, 5.56 military rifle round (Regular barrel, not SBR), and 50 caliber Anti-Material Rifle do to a dinosaur?

Specifically, what would they do to a Utahraptor/Deinonychus (the closest things to a real Jurassic Park Velociraptor), a Tyrannosaurus Rex (let's assume the scary version, not the giant fat chicken), or on the biggest end of the scale an Apatosaurus?

To boil it all down, how would common modern firearms actually fare in a fight to the death against some of the common dinosaurs we see in film and books?

Addendum Different parts of dino anatomy would certainly have different levels of resistance, in the same way that an Elephant's skull is far tougher to crack than a shot to the heart. Please don't assume our humans will be able to place shots on weak points with perfect accuracy or that they will exclusively aim for armored areas. I'm looking for a generalized answer.

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    $\begingroup$ Since you're looking for realism, don't underestimate the common 12 gauge shotgun loaded with slugs, which are reportedly effective even against bears. $\endgroup$ Jun 19 at 16:35
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    $\begingroup$ WHY would you use handguns against tanks? Because that is what this question is asking. When fighting a tank, you use a suitably sized and powered weapon. When attacking a 62-tonne Leopard tank, the relative effectiveness of the nato 5.56mm round is.... not relevant. You would rather discuss the effectiveness of the TOW missile, or a nice 120mm smoothbore firing a nice M829 armor-piercing, fin-stabilized, discarding sabot round. And when fighting a 22 tonne Apatosaurus, you would also employ a suitably scaled and dedicated weapon. $\endgroup$
    – PcMan
    Jun 19 at 17:48
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    $\begingroup$ @PCMan 9mm is a caliber. There are plenty of modern firearms that use this caliber, in fact it is one of the most common for military and law enforcement, as well as for personal protection. Arquebus's and muskets are not still in common use. $\endgroup$ Jun 19 at 20:31
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    $\begingroup$ Guns are ineffective against dinosaurs in dinosaur movies because the dinosaurs in dinosaur movies are not usually dinosaurs, they are a metaphor for something and shooting metaphors is not generally effective. $\endgroup$
    – Brizzy
    Jun 19 at 21:12
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    $\begingroup$ Why are you ignoring the ubiquitous 7.62 NATO round? It's high energy, and guns which shoot it are a lot lighter than .50 BMG rifles. $\endgroup$
    – RonJohn
    Jun 20 at 5:57
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For most dinosaurs just use a living animal of the same size, when possible use ground birds for bipedal dinosaurs. For anything else use a mammal of similar size. Just be aware head shots are less effective the brains are smaller and more well protected than most mammals but not that much less effective. Note, ground birds are harder to kill with bullets than humans (have you heard of the Emu War?) unlike us shooting a hole in a bird's lung does not stop it from working. Also the head is much smaller target and they can can run from shooters much faster. fun little video.

Also be aware these are animals not movie monsters, for the vast majority if you hurt them they will run way. The exceptions to this rule are few and far between and impossible to predict which if any dinosaurs this would be true of.

One thing to consider dinosaurs may be more used to loud noises than animals today many dinosaurs have large sound making structures, so shooting in the air might just get their attention.

Special notes

For therapods, just like in birds, lung shots far less effective, the lungs are much smaller and unlike ours, still work with a few holes punched in them. But otherwise using mammals of the same mass is fine. Saurischian dinosaurs (therapods and sauropods) have bird like lungs while ornithischians have lungs like an alligator which is functionally much more like a mammal lung so mammals can be used for a model without many adjustments.

Ceratopsian be aware a head shot is probably not going to do anything, there can be 4-12 inches of solid bone around the brain. A triceratops shield might even stop 9mm entirely, other ceratopsian frills (shields) have little bone so they can be ignored for the most part.

For heavily armored dinosaurs like ankylosaurs and stegosaurs, which are covered in scutes, thick armor of bone and keratin. A 9mm have a low chance to penetrate, especially on the most heavily armored, a 5.56 might occasionally fail to penetrate due to deflection but a 50 cal will never notice the armor. Otherwise treat as mammals of the same size.

The only dinosaurs you can't come close to with modern animals in size are sauropods. Large sauropods will be tough, their skin is thicker and better armored than elephants and just like therapods they have a bird like respiratory system so lung shots will be weak in effect. Again unlike mammal lungs they still work with holes shot in them. Their sheer size means pistol rounds will be ineffective, even the 5.56 will struggle to actually reach most organs. 5.56 has at best a 20 inch penetration through soft tissue under ideal circumstances, and these are not ideal, we know sauropods have small scutes as well. 20 inches is not going to reach any vital organs unless you hit the brain which would be very very hard, their ribs are so thick they may stop a 5.56 by themselves. So you will need to use a lot of 5.56 because you have to slip between ribs and at the same time rely on blood loss and shock to kill. Stick to the 50 Cal and use a lot of them because you still mostly have to rely on blood loss and shock to kill for the most part.

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  • $\begingroup$ Regarding a dinosaur equivalent that likely wouldn't run away easily, here's another fun little video. $\endgroup$ Jun 19 at 22:45
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    $\begingroup$ Good point about lung damage not being as debilitating as with mammals, but we should also note that it will likely kill them a little later due to blood loss. If it charges directly against you then you're likely dead, so it won't comfort you that the dinosaur will also die a few hours later. But as you said, they are animals. If they see something strange they didn't see before, and then hear a loud noise, they will most likely run away from you instead of towards you. Especially if they feel pain immediately after hearing the noise. $\endgroup$
    – vsz
    Jun 21 at 20:40
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    $\begingroup$ @vsz that will depend on how many bullets they sue and the size of dinosaur, a single lung shot is not a guaranteed kill for an emu much less a larger dinosaur. yes they are animals not movie monsters hurt them and they will run, assuming you are not unlucky and get the super rare species that acts like a boar or wolverine and attack you instead. $\endgroup$
    – John
    Jun 21 at 23:10
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    $\begingroup$ Great answer. It's actually a bit scary that you had this combined knowledge on firearms and dinosaurs. $\endgroup$
    – Stef
    Jun 22 at 9:42
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    $\begingroup$ @JDługosz the bird-like respiratory system, with tiny stiff lungs and lots of air sacs predates flight by hundreds of millions of years. saurischian dinosaurs, all therapods and sauropods, have it, sauropod bodies are filled with air sacs, I worked on paper that showed some of the largest dinosaurs even had hollow ribs.. Ornithischian dinosaurs do not have this system, which is why mammals are a good model. as for noises several ideas for the existence of whiptails in sauropods has them routinely generating sonic booms just like bullwhips. $\endgroup$
    – John
    Jun 22 at 15:38
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Movies like the Jurassic Park series often fail to understand the psychology of dinosaurs, as well as that of even modern animals.

Solitary predators, no matter how powerful, are cowardly by necessity: if they were to receive an injury, they might starve to death before they could recover. When threatened by potential prey that is mounting a potentially effective defense, prudence leads them to seek their meal elsewhere. Consider present-day tigers: they are known to attack humans, but prefer to do so from behind. Wearing a face mask on the back of the head confuses them sufficiently that they don't attack. Which way is that human facing? I'd better not risk it...

On the other hand, predators that operate in cooperative groups can afford to be injured on occasion, as their pack mates can look after them until they can recover. Dangerous prey is no longer automatically avoided unless weaker prey is at hand.

Herbivores can in some ways have more aggressive psychologies than predatory species, particularly if they are herd animals. Herbivores with defensive weaponry are at an advantage if they confidently attack solitary predators, even if it is a bluff, since solitary predators cannot afford to be injured, and both parties know it.

It is a different matter when herbivores are attacked by a pack of predators. The herbivores can no longer defend themselves individually, and so defense becomes a herd task. If an individual is injured, both predator and herbivores know that the injured individual is likely to be singled out as prey.

So, the response of dinosaurs, as well as modern animals, to firearms depends upon a number of factors.

A solitary predator may well run from a gunshot even if not hit the first time it hears one... it might be dangerous. After hearing several shots without being hit or observing another animal being hit, it may conclude that the noise is a bluff. However, if hit, it is likely to flee even if the hit is not crippling or fatal, as it can't afford to take the chance that the next hit won't be worse.

A pack predator can afford to take chances, and is less likely to run from the sound of a shot, or even a poorly-placed hit if the shooter looks like a good meal. They won't likely break off an attack unless the shots coincide with pack members being crippled or killed outright more often than not.

Herbivores - especially if bigger - are likely to attack if they feel threatened or crowded by a single or small group of unfamiliar animal(s) such as humans with guns. They may ignore poorly placed hits in order to eliminate the threat, equating the human with a predator.

This means that a human with a handgun should be able to successfully defend themselves against even a large solitary predatory dinosaur. If Tyrannosaurs are solitary, the mere sound of a gunshot should give one pause, and any hit should drive it off. Being hit by a handgun shot would hurt a lot, even if not particularly effectively placed, and prudence would likely cause the dinosaur to retreat. However, even a handgun shot would penetrate most predatory dinosaurs' hide, and might break a rib or cause a fatal thoracic injury. A long-arm shot would be even more effective.

Pack predator dinosaur species would be more dangerous. A poor hit against one member of the pack probably wouldn't discourage the others, and the human may easily find themselves attacked from multiple directions. It would likely take multiple immediately effective shots to convince the uninjured pack members that this prey is too dangerous to tackle. However, pack hunters tend to be smaller, and would likely be almost as susceptible to handgun shots as humans.

Large herbivores might be more troublesome. Their larger bones mean that lighter, slower pistol rounds could be ineffective, and would merely goad them into pressing their attack. A long-barreled firearm would be advisable to be effective. In particular, armoured dinosaurs such as Ankylosaurus might require a .50" round to penetrate their armour, but most others would be susceptible to regular rifle fire.

Of course, even predatory dinosaurs may change their behavior if they are defending their offspring. In such a case, they may become less cautious in order to eliminate the threat.

Knowledge of firearms by observation can change the behavior of even pack hunters. In Africa, where humans hunt lions, the sight of a solitary human can send an entire pride into a slinking retreat.

Just because dinosaurs had smaller brains doesn't mean that they wouldn't be able to learn from experience. Even for a large, solitary predator, once shot, they would become very wary of future encounters with humans. Pack hunting dinosaurs, being social, would be smarter and even quicker to understand that humans mean trouble if they saw humans shooting other dinosaurs.

Then we need to consider the scale of the meal that a human would provide. To a Tyrannosaur, a human would be a single bite... hardly worth the effort it might take to run it down, unless it was really hungry and the human was really close. Even a Utahraptor pack would get a meager meal from a human... though one human might satisfy a single Utahraptor. Deinonychus packs would probably be tempted by a human, since one would make a half-decent meal for the pack... but if the human pulled out a pistol and started blowing the pack members away, the survivors would soon think better of it. A pack of turkey-sized Velociraptors would get a good meal out of a human, but again, a human with a gun could easily make them find easier prey, even if the pack would have a good chance against an unarmed human.

Huge predatory dinosaurs wading through gunfire - even pistol fire - to eat the humans? I think not!

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    $\begingroup$ Excellent summary of danger versus reward, and the difference having a critical objective to protect versus just having to forage enough makes. $\endgroup$ Jun 20 at 12:31
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    $\begingroup$ In the wild this makes sense. The psychology of animals in captivity is very different from wild animals though. The OP wasn't specific though did bring up "Jurassic Park"-like scenarios. If asking about wild animals, this post is spot on though! $\endgroup$ Jun 21 at 19:50
  • $\begingroup$ to be fair in the original Jurassic park, no dinosaur that attacks humans is injured by them. $\endgroup$
    – John
    Jun 21 at 20:06
  • $\begingroup$ Also to be fair to the original Jurassic Park, it was outright stated in both the book and the movie that the carnivores were unusually aggressive to the humans because they learned humans were easy prey due to poor husbandry procedure on Hammond's part. Hammond kept having "accidents" with his workers due to cutting costs that lead the dinosaurs to become man-eaters much like real big cats (i.e., the very first scene in the first movie) but would rather pay off his workers as necessary sacrifices than put his precious dinosaurs down. $\endgroup$ Jun 22 at 4:07
  • $\begingroup$ @user2352714 Again, a matter of learned behavior. If a carnivore learns that an animal species is easy prey, it will take a fair bit of negative reinforcement to change its attitude. $\endgroup$
    – Monty Wild
    Jun 22 at 10:29
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Big dinosaur

Although there were lots of big dinosaurs, not all were huge. The big ones can often be compared to elephants. A thick hide on a massive beast.

Because of relative sizes a bullet from a handgun doesn't do too much damage. But there is a key word. Not too much. Getting hit is still very much not enjoyable, even if it doesn't penetrate.

In general an assault rifle will penetrate the hide of an elephant. The reason we don't use them is that it is seen as more ethical to kill them in one shot, which is also better for trophies, use of the hide or food. To kill them in one shot they use special guns and ammo, but it certainly isn't a requirement. You can simply riddle an elephant with bullets from an assault rifle or powerful handgun and it'll die very quickly.

Skulls are more difficult to penetrate, as well as their oblique angles make them already pretty good at deflecting bullets. Still the power of an assault rifle against the skull is gery dangerous and multiple can penetrate, if it isn't a single well placed bullet.

The hide can generally be compared to elephants. Where the hide is thicker on a bigger specimen, an assault rifle is likely still able to penetrate. Again, firing many bullets will likely incapacitate the target, if not do lethal damage.

But in one of the later jurassic movies they tell us the solution as well. On the helicopter there is a gatling gun. Likely they had extra security for a big dinosaur escaping, especially as they were experimenting with a militarised version. As one person states very well, they will take the helicopter and turn the big dinosaur into red mush.

Smaller

The smaller dinosaurs like velociraptors do not have any appreciable advantage in armour. Nearly any gun will do. These dinosaurs as a weapon, like suggested in one jurassic movie, is quite ludicrous. They might be fast, but also big. They are melee, which is something rightly phased out of most military engagements. Velociraptors can only bank on the element of surprise, but even then they can go down quickly to any experienced infantry group.

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    $\begingroup$ "On the helicopter there is a gatling gun" this.. appropriately scaled weaponry for the task. NO-one hunts a blue whale with a handheld speargun. So why would any sane person hunt an equally big apatosaur with a handgun? $\endgroup$
    – PcMan
    Jun 19 at 18:26
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    $\begingroup$ FYI you made a small typo in “ skull is gery dangerous” :) $\endgroup$ Jun 19 at 20:10
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    $\begingroup$ @PcMan To assert your dominance. $\endgroup$
    – DKNguyen
    Jun 20 at 0:55
  • $\begingroup$ Many large predatory dinosaurs had quite flimsy skulls. Allosaurus had the ability to expand the width of their mouth so as to be able to swallow huge chunks of meat. Really only their brain case was solid. $\endgroup$
    – Monty Wild
    Jun 20 at 1:49
  • $\begingroup$ Velociraptor seems to have weighed in at about 15 kilos which is about the same size as a mid range domestic turkey. Potentially dangerous? Yes! But provided you can hit it center of mass just about any caliber in any firearm above .22 would suffice. $\endgroup$
    – Mon
    Jun 20 at 2:17
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I don't think you need any special guns, the trick is in the ammunition. Sure, maybe the skull of a dinosaur is much tougher than that of an elephant, but is it tougher than steel plate? Because we make bullets for common hunting rifles that will go through steel plate; steel or tungsten core rounds, commonly referred to as armor piercing rounds, should have no problem getting to a dino's brain or heart. Personally I would go for the heart. I don't know how big dinosaur brains are, but I'd guess they're significantly smaller than their head, whereas the heart of an animal that huge must also be huge. If I don't care about being humane, shooting it in the hip or pelvis could be a good idea; who cares how mad I make it if it can't get to me because it can no longer walk?

In the US at least, this ammo isn't all that rare either, civilians in many states can easily buy it.

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  • $\begingroup$ The gun matters. You can't just put high-power ammo into a flimsy gun not designed for it, or you will damage the gun, possibly with catastrophic effect. $\endgroup$ Jun 19 at 23:36
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    $\begingroup$ @LawnmowerMan Armor piercing rounds don't use more powder, the pressures involved are similar. They penetrate better because the round doesn't deform when it hits the target. Here's a representative video: youtube.com/watch?v=cANMtJNdrTQ tl;dw, a normal 30-06 M1 Garand shooting steel-core ammo penetrates a 3/4" AR500 steel plate. $\endgroup$
    – Ryan_L
    Jun 19 at 23:53
  • $\begingroup$ As you can see here: kwk.us/pressures.html cartridge pressures can vary from 20-65,000 psi. Obviously, a gun designed for a lower-pressure round is not going to fare well when loaded with a high-pressure round. The point is that matching the rifle to the ammo is necessary. $\endgroup$ Jun 20 at 4:45
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    $\begingroup$ @LawnmowerMan Armor piercing rounds are the same caliber. Same amount of gunpowder, same sized shell, same sized projectile. The only difference is that armor piercing rounds have steel or tungsten cores instead of being made of lead. They're not bigger bullets, they don't generate more pressure. That chart compares pressures of different calibers, not different projectile types. A hollow-point or FMJ 30-06 shell will generate similar chamber pressures as an armor piercing 30-06 shell. $\endgroup$
    – Ryan_L
    Jun 20 at 5:22
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    $\begingroup$ If it came from a store as opposed to some idiot using the wrong powder while reloading, and the cartridge was MADE to chamber into the weapon ('it fits' doesn't count), then it is safe to fire provided the weapon itself is in correct operation. $\endgroup$
    – Mazura
    Jun 20 at 21:41
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Do you want to stop the dinosaur or kill it?

There's a difference between instantly (or at least very quickly) stopping an animal with a shot and just wounding it so that it eventually dies (or even recovers). What good will mortally wounding a dinosaur do if the dinosaur will still maul you before it collapses?

To stop an animal, shot placement is very important. You want to hit in the vital organs of the nervous or circulatory system. However, as depicted in movies, people attacked by dinosaurs usually shoot chaotically in the general direction of the threat. This certainly makes firearms much less effective than they could be. If you don't hit vital organs and your target doesn't decide to give up after being shot, you will have to wait until it bleeds out enough to drop the blood pressure in the brain below the unconsciousness threshold.

In below verdicts I assume shots to the torso. And of course these verdicts are highly speculative.

Common pistol rounds, such as 9x19mm, usually use round-nose bullets, which are not ideal against even soft body armor. Not sure whether that translates to performance against thick skin of large dinosaurs. They also have lower energies than rifle rounds. Verdict: moderately effective against Deinonychus.

5.56x45mm NATO and .223 Remington are similar and for our purposes we can treat them as identical. In some states they are not legal to hunt deer with1 because when the shot placement is not ideal, they might wound the deer instead of killing it quickly. When wounded, deer tend to run away and hide. Still, it's not like deer-sized animals can just brush it off. Verdict: effective against Deinonychus.

12.7×99mm NATO (.50 BMG) is a very powerful round which is successfully used against vehicles and should also be highly effective against dinosaurs. Verdict: highly effective against Tyrannosaurus Rex. Effective against Apatosaurus.

You left out an intermediate option between "possibly too weak" and "overkill": 7.62×51mm NATO (which for our purposes is the same as .308 Winchester). It is widely used for hunting medium to large game and therefore should be effective against most dinosaurs of comparable sizes. Verdict: highly effective against Deinonychus. Moderately effective against Tyrannosaurus Rex.

Another intermediate option are shotgun slugs. Muzzle energy of a 12-gauge slug is typically higher than the muzzle energy of .308 Winchester2. On the other hand slugs are usually blunt, which may limit penetration in large dinosaurs. (And you need a lot of penetration against large dinosaurs.) Verdict: highly effective against Deinonychus. Moderately effective against Tyrannosaurus Rex.

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Depends on what you want to hunt

An article I read estimated the average size across all species at their peak was about the size of a pony. Which means depending on what species it is you are hunting means the vast majority of species would have been easily dispatched with any medium caliber rifle or larger caliber handgun. (Velociraptor was turkey sized as an example.)

Remember also that the number of individual species in any environment declines with size. So even in the late Jurassic/early Cretaceous at the peak of their reign the landscape would have been dominated by numerous small species of (dinos and others) with the number of individual species declining rapidly as size increased.

There is some evidence for instance that suggests T Rex was the only large predator over most of its range because it's juveniles filled the niches that would have been taken by other medium sized species. Same with sauropods, yes there are fossil records of a large number of different species spread across time and region. However only a handful of species, if that could have co-existed at any one time in any one locality because the ecology couldn't sustain more.

So if the issue is protecting yourself I'd go with a military grade firearm in a military grade calibers (EDIT: to clarify that's standard military grade assault rifle calibers - in a standard issue modern military grade assault rifle) and to hell with sportsmanship. Better alive than ending up as fossilized dino scat for some archaeologist to dig up. (Hey how'd that tooth filling end up in there?).

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    $\begingroup$ "military grade firearm in a military grade calibers and to hell with sportsmanship". That's a very poor -- and essentially meaningless -- answer, given that there's such a huge range of military grade calibers. $\endgroup$
    – RonJohn
    Jun 20 at 5:46
  • $\begingroup$ In this context military grade firearm refers to .556 or .308 or their Russian counterparts being the dominant military calibers in the world today. Since I've already d=frames the answer as being for personal defense and not hunting large dinosaurs anything larger e.g .50 cal is off the table. but for the pedants amongst us I'll amend the answer to state the bleeding obvious. $\endgroup$
    – Mon
    Jun 20 at 22:34
  • $\begingroup$ But lots of sportsmen use .556 and .308. Heck, .308 is a sportsman's cartridge (en.wikipedia.org/wiki/.308_Winchester) and .556 in an AR-15 is perfectly adequate to deer hunting. $\endgroup$
    – RonJohn
    Jun 21 at 2:05
  • $\begingroup$ Yes that's the point, if the average dino was pony sized or smaller unless you have deliberately decided to go hunting larger prey then the average rifle caliber will suffice because that's the size of animal your more likely to encounter. The only other option is to carry a big game rifle at all times and hope that first or second shot gets the small/quick predator that's looking to turn you into lunch. (And then hope that its alone). $\endgroup$
    – Mon
    Jun 21 at 2:28
  • $\begingroup$ Carry a 12 ga. pump action or semi-automatic shotgun with multiple types of shells: slug, 00 buck and bird shot in their own magazines or quick-load tubes. Maybe 10 ga. would make a comeback. $\endgroup$
    – RonJohn
    Jun 21 at 2:42

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