So we’ve all been there; you ran your big mouth around the wrong people and now they’re
trying to gun you down.
Of course, normally you’d just whip out your side-arm and smoke the motherflippers,
but this time you’ve only gone and left your trusty pistol at home! Nightmare!
As you run for your life with deadly assailants hot on your tail - and who hasn’t - you
conveniently pass by a large body of water and remember all the TV shows and films which
show heroes avoiding a hail of bullets by simply diving underwater… but exactly how
realistic is this?
I’m Stu, this is Debunked, and we’re here to sort the truths from the myths, and the
facts from the misconceptions.
As you can imagine, firearms are a diverse group of weapons that work differently depending
on type, design, ammunition etc., but in general most guns do not play well with water. Firing
into water from above the surface is far less effective and significantly less lethal than
your usual land-based gun shenanigans.
This is because most guns are designed to propel bullets through the air, and while
air resistance obviously has an effect on how fast and far a bullet can travel, it certainly
hasn’t stopped us from pumping each other full of lead for hundreds of years.
Water on the other hand provides substantially more resistance. As a bullet travels through
water it collides with an unfathomable number of water molecules.
Each individual collision causes a miniscule amount of energy to be transferred from the
bullet to the molecule. This continues until the bullet is depleted of energy and the bullet
comes to a stop. Due to the density of water this energy transfer occurs at a rate significantly
faster than when the bullet pushes through molecules in our air,
meaning it has less energy to push through your body.
For comparison, regular, garden-variety air only weighs around 1.25 kilograms per cubic
meter, meaning it is fairly easy to fire bullets through the atmosphere with deadly force.
Whereas water weighs roughly 1,000 kilograms per cubic meter, making it somewhere in the
region of 800 times denser than air.
Obviously, this dramatically changes the lethality of firearms built to operate at standard atmospheric
pressure.
Now, the speed a bullet can travel through water and the distance it is able to travel
is highly dependent on its angle of entry.
Studies have shown that…
standard projectiles fired at angles of 5º to 15º from the water’s surface are unlikely
to even enter the water, as they tend to either ricochet off from the surface or break up
into pieces upon impact.
One study conducted in 2008 at the King Abdullah University of Science and Technology found
that…
“most standard bullets appear to enter successfully only when ﬁred above 11 degrees”,
…so if your bad guys are firing at you from a particularly shallow angle, they aren’t
going to pose much of a threat to you at all. Bad news for your would-be killers.
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Let’s return to today's important task, surviving bullets underwater…
because now you’ve got enemies coming at you from all angles, and they’ve got some
pretty serious hardware pointing right at you. How deep are you going to need to dive
to dodge their murderous metals?!
Well, the surprising factor that you have on your side is that the more serious the
hardware, the less threat they may pose to you while you’re underwater.
Believe it or not, the bigger the caliber of bullet and the faster the muzzle velocity,
the shorter the distance it will travel after entry into the water. The brainiacs over at
Mythbusters came across this phenomenon while investigating this particular quandary.
They fired a .223 caliber bullet, which leaves the barrel at a supersonic 2500 feet per second
or 2700 kilometers per hour, followed by a whopping .50 caliber bullet which travels
at a staggering 3000ft per second or around 3300 kilometers per hour.
When these bullets hit the water’s surface, both bullets essentially exploded into pieces,
and their lethality would have been totally eliminated again within 2 to 3 feet (or just
under a meter) of water.
Incredibly you’re actually in a lot more danger if your pursuers are all carrying handguns.
A 9mm bullet travels at a comparatively slow, but still pretty rapid 1300 ft per second
or just over 1400 kilometers per hour.
So what makes this the more deadly bullet?
Well, when an object enters the water it encounters resistance,
and the faster the object is traveling the greater the resistance it will experience
as it enters this new state of matter. This resistance causes the object to decelerate.
In our case, we have lower velocity bullets like a 9mm traveling at a respectable 400
meters per second, the deceleration it experiences occurs over a couple of meters.
Over this distance it is depleted of energy, it slows to a stop and then sinks to the bottom.
When higher velocity bullets enter the water on the other hand, they experience substantially
more resistance. Whilst a slower bullet can displace the water in front of it relatively
easily, at the staggering velocity of a 50. Caliber bullet there simply isn’t enough
time to move the water out the way.
The massive resistance this exerts on the bullet can exceed the bullet material’s
strength, causing it to deform or disintegrate into multiple pieces as it enters the water.
The huge resistance and loss of energy required to tear the material apart mean that in certain
circumstances a faster bullet
can end up traveling less far than its less speedy counterpart.
So, when a puny little 9mm bullet is fired into water from a vertical angle, it could
mean the end for you unless you dive relatively deep, because one of these will be lethal
to a depth of 7 ft or just over 2 meters below the surface!
Meaning you’d need to get down to 8 feet or lower to ensure you didn’t even sustain
a flesh wound.
But hang on, if it's the impact with the water’s surface that’s causing the bullet to initially
decelerate so much and lose the majority of its energy, why doesn’t your trigger happy
pursuer hop into the water with you and shoot at you while they’re fully submerged?!
...Oh, sorry.
But don’t worry too much, because for a technology that already doesn’t mix well
with water, dunking your average firearm in good ol H₂O is not a good idea.
Even though some firearms, like glocks, can generally be relied upon to fire underwater,
this is not true of most guns, and even when they do discharge fully submerged, the results
are often far less than adequate.
As soon as you dip a gun under the surface, water almost immediately feels up all the
various nooks and crannies it can reach. First and foremost, water can soak into the cartridges
themselves, making the propellant too wet to ignite, preventing the gun from firing
at all.
That being said, modern cartridges are often watertight. However, even if the firing pin
has managed to ignite the gunpowder grains, the bullet’s problems don’t end there.
When a bullet is fired underwater, rather than into water, the increased resistance
of squilions of water molecules are acting upon the bullet from the moment it is fired.
This means that the bullet will have to push against all this water, which may weigh considerably
more than the bullet itself, before it even exits the barrel.
So naturally the bullet’s muzzle velocity, i.e. the speed at which the bullet is traveling
the moment it exits the gun barrel or ‘muzzle’ is drastically reduced.
But how far away would you need to be to dodge this amphibious lead?
Well once again, some televised lunatic has actually tested this. In 2015,
Norwegian physicist Andreas Wahl decided to investigate this exact situation on a Norwegian
TV show called ‘Life on the Line’, in which he demonstrates scientific principles
in a variety of seemingly dangerous ways.
Standing in a pool with all but his head underwater, Whal positioned himself directly in the line
of fire of a submerged firearm,
this time an AG3 Assault Rifle which, on land has a muzzle velocity of 2625 ft/s (over 2800
km/) and has an effective firing range of around 1300 ft or 400 meters.
When the gun fired, the bullet traveled less than a meter before slowing down almost entirely,
then sinking harmlessly to the bottom of the pool.
So, in each scenario, you’ll only have to be a few feet away from your assailant to
avoid being hit.
Still, your would-be killer may yet have a very slight chance of success in the highly
unlikely event that they have a very specific type of weapon to hand.
These weapons often differ from conventional guns in a number of ways. Firstly, they often
don’t fire regular bullets, but dart-like metal bolts which move through the water far
more easily than their bulky, rounded counterparts.
Some of these weapons also utilize pressurized gas instead of combustible propellants, avoiding
the usual issues with submerging cartridges in water.
Underwater firearms are also frequently made without helical grooves - or rifling - on
the inside of the barrel, as the bolts rely on the hydrodynamics of water to maintain
a steady path on the way to their target.
Meaning weapons like the Soviet APS Underwater Rifle, aren’t technically rifles.
As a result, underwater firearms can have an effective range of up to 30 meters (or
almost 100 feet) at shallow depths, though this is significantly lessened the deeper
you go.
Still, better than only a few feet.
If your enemy happens to possess one of these guns, jumping into water will provide you
with far less protection than with regular firearms.
In addition, there is the possibility of using special “supercavitating” rounds that
are specially designed to penetrate deeper into water than your standard run-of-the-mill
bullets.
They are made with flat tips that push the water around its sharp edges extremely quickly,
causing a drop in pressure that creates a gaseous cavity around itself.
This drastically reduces the bullet’s contact with the water, preventing skin friction drag,
and thereby allowing it to
slice through the water much faster and further than conventional bullets.
Instead of stopping or even breaking apart after a few feet, supercavitating bullets
can be accurately fired as far as 60 meters (or just under 200 feet) into water,
rendering your once ingenious aquatic defenses effectively useless.
Ultimately however, it’s clear that diving sufficiently deep underwater can protect you
from all but the most specialized weaponry.
Still, probably best not to trigger people with guns in the first place, m’kay guys?