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When writing stories I usually use war as a simple and understandable way to introduce a conflict that needs to be resolved or sweeps the character away.

To keep it interesting I need to build versatility into the weapons and gear of the characters. After all at best I can say "he hits/misses". It's everything around it that matters: what the characters do, what they have available, how they react to the situation, how they react after it's conclusion, what they do afterwards and how they react the next time. For this reason I look at various things like gadgets (jumpjets) and the choice of weapon they carry.

A sniper is relatively boring. It's the penultimate "your shot hit or misses" weapon. It only becomes really interesting if you fight another sniper or create situations where they need to use environment (thunder) to hide their shots. It's severely limiting in the type of story you tell.

A machine gun or rifle offers more versatility for a story, but the weapon I go to is the shotgun. It is a close-quarters weapon and allows me to let the characters get into hand-to-hand combat, you can equip a large variety of slug ammunition and it is far less clean than the "hit enemy far away and ignore the bodies aferwards" storytelling I dislike.

Among the ammunition I would want to have armor-piercing slug ammunition. However general concensus is "this slug I heard off didn't have the speed and couldn't penetrate so none can". So I want to have a solid and above all complete answer on how exactly an armor-piercing shotgun slug could be fired by a shotgun, or why not.

For reference: many sniper rifles have shorter barrels, even the anti-material rifles have a maximum barrel length akin to that of some shotguns and the closest size in barrel diameter. Yet when people talk about shotguns it is a solid "impossible" with statements of what some slugs can achieve rather than what is possible.

To make the title clear with my full question:

How could a shotgun fire armor-piercing ammunition effectively?

Extra information:

  • this question is about both the shotgun and the slugs. If you need to redesign both the shotgun and slug to be effective that is possible, as long as the shotgun remains a shotgun in functioning.
  • this question is about what is POSSIBLE, not about a list of what is not possible. If you have something that makes it impossible, explain what would be necessary to make it possible and why that is unattainable.
  • the answer with the best AP ability is the best answer, unless a reasonable and detailed answer can be given explaining why it is impossible.
  • a lower accuracy is acceptable as long as it's not a cointoss to see if you can hit the side of a proverbial barn.
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    $\begingroup$ It's not just a hit or miss! The concrete flying from the impact grazed his cheek, scoring a tiny red line from which a few red drops swelled and then stopped. The second hit the skull, but the angle caused it to deflect. Still, skin hung ghastly from the side of his face. The next pierced her leg. She felt the bullet pierce the kevlar and then the skin. Only afterwards she realised how she had felt tendons snap and the bullet spin out of her leg at a strange angle. That being said, I agree being close to the action can help a lot for a story. $\endgroup$
    – Trioxidane
    Jun 8 at 11:50
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    $\begingroup$ BTW, the question should explain what is the difference between specifically a shotgun firing armor piercing ammunition and any old generic smoothbore firearm? As far as I understand, a shotgun is a firearm specifically made to fire shot; most of them can fire slugs, but that is not their primary function. But then, I'm a European with limited knowledge about firearms, and would be delighted if the question was edited to include the basic explanation for the benefit of people like me. $\endgroup$
    – AlexP
    Jun 8 at 12:02
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    $\begingroup$ Just to be clear, we're talking body armor not tank armor, right? $\endgroup$ Jun 8 at 12:17
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    $\begingroup$ Obligatory youtube channel TAOFLEDERMAUS $\endgroup$
    – MolbOrg
    Jun 8 at 13:08
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    $\begingroup$ Penultimate = the next-to-last item in a series. You really want the "ultimate" weapon unless you want the second best. $\endgroup$
    – MTA
    Jun 8 at 19:44

10 Answers 10

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Generally, armor piercing ammunition is high velocity, and high velocity in firearm rounds is inseparable from high chamber pressure.

Problem is, a shotgun is a low pressure weapon. Typical shotgun chamber pressures run around 15000 psi (approximately 1000 bar, 100 MPa), while high velocity rifle rounds typically run three times that level. So, in order to get a high velocity from a shotgun, you've have to use the other method: a very light projectile for its bore size.

This points to discarding sabot rounds, which have been sold in various forms for rifles and muzzle-loaders for decades. With a discarding sabot, it should be possible to get a bullet comparable to a common 7.62 mm rifle slug to a velocity roughly similar to the 900+ m/s (~2800 ft/s) you'd get from a military rifle, which is fast enough for an armor piercing bullet to work the way it's supposed to.

Unfortunately, there's another problem: the smooth bore. An armor piercing bullet needs to strike pretty precisely nose on to shed its windshield and let the penetrator, well, penetrate armor. Without rifling, the round must be aerodynamically stabilized (as is the case with most kinds of common shotgun slugs -- they have a heavy end, which travels to the front, and a light end, that acts as vanes to stay at the back).

In the end, you wind up with a projectile that looks rather like some modern tank rounds, specifically fin stabilized armor piercing (the main gun on an Abrams tank is a smoothbore!). This round uses a "piston" base to seal the bore and get the most possible propulsion from the powder charge (while staying within the shotgun's rather low pressure limits), is very light compared to common slugs, and once it leaves the bore, separates from the piston to become what amounts to dense, hard metal arrow. Assuming the physics works out right to get the velocity needed, this should penetrate body armor and even light vehicle armor as well as a round from a 7.62x51 NATO chambered rifle.

There's one other slight issue -- accuracy. There is simply no way for a smoothbore round in this size class to be as accurate as a rifled one. A match grade rifle can shoot to accuracy of better than a minute of arc, giving a useful range of more than a kilometer. A tank gun (also a smoothbore) is about that good (though some of that is due to its targeting systems). A shotgun, on the other hand, has a relatively thing barrel wall that is easily deformed, and typically isn't equipped with a scope sight as you'd see on a sniper rifle. They can be accurate enough for hunting to a range up to a couple hundred meters/yards, but that's hitting a pie plate, not an ear.

This means AP rounds for a shotgun will have a relatively short effective range -- not because (like normal shotgun ammunition) they lose velocity quickly, but because they have limited accuracy. They'd be effective to a couple hundred yards/meters; beyond that, if they hit, they'll still penetrate out to double that range or more, but the probability of a hit drops off pretty badly.

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  • $\begingroup$ You mention low pressure limits of the shotgun. If the shotgun was made differently, like say a smoothbore version of an anti-materiel rifle, would you be able to handle higher pressures and maintain shotgun capabilities when firing low-pressure charges? Anti-materiel rifles seem pretty similar in many ways to shotguns and have solved the low-pressure problem allowing up to 1000m/s or more muzzle velocity. $\endgroup$
    – Demigan
    Jun 8 at 15:08
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    $\begingroup$ @Demigan Sure, you could build a smoothbore gun like a Barret/Browning .50 -- but then it wouldn't be a shotgun, even if it had a smooth bore. It would be a smoothbore anti-materiel gun. A shotgun is lightweight, relatively low capacity, derived from a sporting arm rather than a military one. Anti-materiel rifles need range and accuracy comparable to sniper rifles, but in heavier caliber for killing trucks and tractors. $\endgroup$
    – Zeiss Ikon
    Jun 8 at 15:43
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    $\begingroup$ The OP did mention he wants close range fire-fights, so the "disadvantages" of the weapon system sound like advantages for sake of the OP $\endgroup$
    – Nosajimiki
    Jun 8 at 15:44
  • $\begingroup$ @ZeissIkon ignoring the increase in cost, would it be possible to limit what parts of the barrel are high-pressure resistant? Pressure drops off quickly as far as I'm aware, if "only" the chamber and a bit of the start of the barrel require this heavier material perhaps the weapon can remain relatively lightweight. $\endgroup$
    – Demigan
    Jun 8 at 17:09
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    $\begingroup$ @Demigan This is called a "chamber reinforce" when they do it on a cannon. It's of limited utility, because you'd also have to build the gun with a strong enough lock to take the bolt thrust (this is why rifles usually have the rotating bolt, "interrupted thread" lock). You'd be essentially trying to design a rifle to be light enough to handle like a shotgun, and all you're gaining is the large, smooth bore -- which isn't an advantage for a gun that can do what a rifle does. $\endgroup$
    – Zeiss Ikon
    Jun 8 at 17:15
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Taofledermaus has your answer.

Custom SHOTGUN Slug DEFEATS AR500 Body Armor

polycarbonate slug

armor plate

I was thinking - OK, how about a 8 gauge goose gun with an aerodynamic tungsten slug... Then I realized that this channel is all about that kind of stuff, which I know because I have watched a ton of their videos.

This polycarbonate slug is not very heavy - it is basically plastic! It was fired from a standard shotgun with birdshot-type propellant. It flew like crap and so innovations from other slug types (as seen on this channel) could be used to improve aerodynamics. In fact the maker of these slugs did exactly that as shown in a later video, using an air rifle pellet shaped carbon fiber slug with a similar tungsten penetrator

So large, low density, low velocity. But that tip in there is tungsten carbide which is super dense and very hard. It was delivered to the armor plate by the plastic, and the tungsten penetrator went right thru and also right thru the big squash behind it.

So - not overpowering the armor with giant masses and velocities. Delivering a small and very hard penetrator is how these armor piercing shotgun shells work.


For your fiction might I suggest different schools of thought as regards optimal custom shotgun shells for their applications. Your characters can debate, point out flaws, mock, admire and generally engage one another over these issues which as you state is the stuff that drives a story.


@Nepene Nep - check out the video. After this plastic and tungsten weirdness, they try a sniper rifle against the same plate and squash. No dice.

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    $\begingroup$ Their sniper rifle would probably have worked better for this if they fired AP machine gun ammunition from it (yes, they make that in 7.62x51, for light machine guns like the M240). I've seen a .30-06 (aka 7.62x63) AP round punch right through heavy angle iron... $\endgroup$
    – Zeiss Ikon
    Jun 8 at 15:47
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    $\begingroup$ Or instead of an inert penetrator in a plastic slug, replace the plastic with a shaped charge that detonates on impact. $\endgroup$
    – jamesqf
    Jun 8 at 17:43
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    $\begingroup$ Looking at several of his video's there seems to be a lot of improvements possible. Most AP slugs seem to suffer from stability issues, if those could be resolved with (costly) solutions probably taken from tanks it could help with penetration power. The AP slug fired in the video looks like many of the slugs fired there: A quick project or low-cost idea rather than a deliberate and heavily tested design. I would hazard a guess that if it were a sabot and the penetrator was more dart-shaped it would work much better already. Not to mention James's idea of a HEAT round. $\endgroup$
    – Demigan
    Jun 8 at 18:33
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    $\begingroup$ That AR-500 plate is rated level III. Military grade body armor is typically level III+ or level IV. This means that it is rated to stop most civilian grade weapons like handguns, shotguns, and low-caliber rifles firing non-armor penetrating ammo. But, military personnel typically use level III+ or IV body armor. So that test conclusively shows that you can make a cop-killer slug this way, but is inconclusive about if it would make a viable military grade armor-penetrator. $\endgroup$
    – Nosajimiki
    Jun 9 at 14:09
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    $\begingroup$ Also, it's worth noting that the rounds used in that video extend in front of the normal dimensions of the shotgun shell. Most slugs are contained inside the shell. This means some of the stopping power being shown may be coming from overloading the shell with propellant. This is dangerous if your shotgun is not designed to deal with the extra shock, and it would also jam if you wanted to put these in anything other than a break-action shotgun. $\endgroup$
    – Nosajimiki
    Jun 9 at 14:21
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There are many ways that modern munitions can defeat armor. Most traditional firearms do it with a hardened metal jacket or tip, but getting the velocity you need for this out of a stock-shotgun is not really doable. Even a saboted round will only get you up to an okay level of penetration.

So, instead of looking at how riffles pernitrate armor, you could try looking at how RPGs do it. Anti-armor RPGs have much lower muzzle velocities than riffles, but use a larger projectile assisted by impact explosives. Converting a shotgun into a mini-RPG like weapon is a pretty trivial task when you consider how similar they are.

Your best options are probably going to be a HEAT or HESH type round:

A HEAT round uses a detentator pin that leads in front of the shell to set off a shaped charge just before it impacts the target. This directs the explosive into a narrow high energy stream the blasts a tiny hole through the target filling the area behind the impact with a spray of VERY hot metal.

A HESH round is tipped with a plastic explosive and places the detonator cap at the very back end of the projectile. This way the slug spreads the explosive out against the target before detonating allowing for a maximum amount of energy to be transferred into the target which then relies not on penetratingly the armor, but sends a shock wave through it.

enter image description here

I'm not sure how effective a HEAT or HESH round would be against a Lightly Armored Vehicle because even if you beat the armor, filling the cabin with enough HEAT spray or spalling debris to take out people inside with such a small round would be hard, but if your goal is to beat Class III or IV body armor, either solution should do fine. When your armor is pressed right up against your squishy bits, the shockwave of a HESH round would cause MASSIVE internal injuries even if your armor technically stops the shot, and a HEAT round does not need to fill an entire vehicle cabin, just the area directly behind the impact point.

Here you can see what happens when you turn a slug into a high explosive armor penetrator: https://www.youtube.com/watch?v=8Lpx_CQ6kwo. While this video is labeled a HESH round, it's actual configuration appears to be some sort of a bastardized hybrid between a HESH and a HEAT round, but either way, you can clearly see just how much extra power you can put into a target, even with a relatively small explosive shell.

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  • $\begingroup$ HEAT = High Explosive Anti-Tank, but what does HESH stand for? Apparently en.wikipedia.org/wiki/High-explosive_squash_head $\endgroup$ Jun 10 at 2:12
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    $\begingroup$ I was about to say exactly this. Plus: both types of round are also fired from smoothbore barrels ( a "problem" that other answers mentioned). Plus you're using the advantages of a shotgun: a lot of material reaching the target, while being able to ignore its downsides (not much speed/force behind the hit), since our shell only needs to be fast enough to detonate properly $\endgroup$
    – Hobbamok
    Jun 10 at 8:44
  • $\begingroup$ I was about to post HESH but you beat me to it :-D $\endgroup$
    – Gustavo
    Jun 11 at 16:06
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Sniper rifles.

They can target vehicles, threaten people who you call, kill passerbys, disable communications, do lots of things in chase scenes, and do lots of things outside of just killing. Snipers have a wide ability to influence their environment. They also have a voyeurism aspect where you can spy on stuff you're not supposed to see which can make for fun scenes. Sniper battles are popular in fiction, for a reason.

Armor piercing shotgun rounds

You can make saboted rounds that can penetrate armor. The common criticism people make is to John Wick 3 which had rounds that wouldn't penetrate based on their nature, but you can make fairly narrow ones that have a spike that can penetrate armor. It would be weird from a military perspective since rifle bullets penetrate armor much better, but shotguns tend to be more legal than rifles, so there's some market for such weapons.

Such rounds are a lot more expensive than normal shotgun slugs (5-10 times more expensive), but that's not a big issue for many story protagonists. Shotguns are widely legal, mostly short ranged weapons that are cheap to make and run, as a general matter. Shotgun slugs are cheap to make and great for handling within 100 meters targets who lack armor. Making them armor penetrating is expensive, but possible with enough money.

You can also use explosive shells, which are also very expensive, to improve penetration.

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  • $\begingroup$ You also have high explosive rounds like the frag-12, they should penetrate body armor. $\endgroup$
    – John
    Jun 8 at 13:16
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    $\begingroup$ This brings up a good question as to WHY a group might prefer shotguns. A resistance or insurgency group could have a very hard time arming itself with assault rifles and the associated ammo, but shotguns are both much easier to get for "civilians" and the ammo is much easier to customise using common tools since you don't need to worry about riffling or high precision tooling. Just cut off the front of a normal shell and replace the shot with whatever payload you desire. Explosive/sabot shells would be labor intensive to make by hand, but in many ways easier than modern bullets. $\endgroup$
    – Nosajimiki
    Jun 9 at 14:41
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I would like to go with the simplest answer here, as the other answers are awesome and cover things like SABOT rounds excellently.

Shotguns can fire frag grenades.

So, yeah that takes care of most armor, but it gets better. If you haven’t seen it already, look up the AA-12. Go on, I’ll wait here. Got it? Ok cool. This is a fully automatic shogun with 100 and even 200 round drum attachments that can fire 12 gauge frag grenades multiple times per second. Any kind of personal armor will soon be rendered completely superfluous.

For some bonus points you could also consider incendiary rounds. Armor doesn’t matter if the person wearing it is on fire. Also you could probably make a shotgun fire sticky explosive rounds pretty easily, but you would have to reduce the muzzle velocity, thus hindering range. You could also use flechette rounds, which is a bundle of super hard, thin, razor sharp needles that can defeat armor fairly well.

BUT WAIT, I’m about to blow your mind again! The easiest method for dealing with body armor when using a shotgun is…. Firing normal slugs. Will they penetrate? Probably not. Shotgun slugs are big, soft, blunt, and (relatively) slow. However, what they will do is dump lots of kinetic energy into a tiny little spot. This tends to do things like break bones, rupture organs, cause internal bleeding, and a generally rough few days afterward. Though it may not be lethal, in many cases it is better to disable your opponents instead of killing them. This not only takes them out of the fight, but also their friend who now has to drag their buddy back to safety. So 2 for the price of 1!

A few important points you may want to remember.

  1. Shotguns have longer range than most people think, but not anywhere near the range of even the most basic rifle.
  2. Shotguns only carry around 8 or 9 shells unless they use a magazine, and you usually have to reload shells one at a time.
  3. Shotgun shells are very heavy, their magazines are much heavier, which limits the ammo you can carry.

Modern militaries do use shotguns, usually as a breaching tool, though they are extremely useful when it comes to clearing the building you just breached. They are great for any close quarters fighting because of their stooping power, but remember, a rifle works just fine at close range too, and it works at ranges a shotgun can only dream of.

None of these points means that this premise won’t work, but depending on the audience, tone, and scientific accuracy of your story, you may want to consider them and develop a reason why your characters are using shotguns over rifles. Remember, rifles can pierce armor too, and some sniper rifles can pierce 1 inch think steel plate from over a mile away.

Also! If you would like to research specific, commonly used weapons here you go!

Shotguns

  1. R870 Wingmaster: Possibly the best selling shotgun ever, definitely the best selling shotgun in America, fantastic weapon and very commonly used.
  2. Mossberg 500: The number 1 European shotgun and commonly used by police and militaries all over Europe.
  3. AA-12: Possibly the coolest shotgun ever, full auto, recoil dampened, titanium barrel and frame, pure awesome.

Rifles

  1. M4 and variants: Long range, high fire rate, 5.56 caliber ammunition but can be converted to .50 caliber pistol rounds. NATO’s favorite weapons system.
  2. AK-47 and variants: Usually 7.62 caliber rifle with heavy stopping power but lower accuracy and fire rate.
  3. SCAR and variants: NATO’s counter to the AK, also often 7.62. Hard hitting with better accuracy and highly modular design.
  4. Tavor: Very cool, bull pup in 5.56 and 9mm, short, excellent accuracy and fire rate, and the 9mm version can be silenced very well.

Sniper Rifles

  1. Barret .50: Semi auto sniper rifle, technically an anti-material rifle, effective range is around a mile and a half though the bullet is still lethal at much longer rangers.
  2. M-200 intervention: Maybe my favorite sniper of all time. 408 Cheytech rounds, basically a necked down .50 caliber casing with a smaller bullet. Flatter trajectory, effective range out to either 2 or 2.5 miles. It’s also bolt action which means very high muzzle velocity.
  3. .338 Lapua: Technically a round and not a rifle, but often called the best sniper round ever. I don’t have as many details on it as the other rounds but it is exceptionally accurate.

Hope this helps!

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    $\begingroup$ "Firing normal slugs. Will they penetrate? Probably not." Does it matter? No. "Any 12 gauge round is gonna just kill through deformation and energy transfer, it's not going to penetrate..." – AR500 Armor®, YouTube $\endgroup$
    – Mazura
    Jun 9 at 3:05
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    $\begingroup$ @Mazura Exactly, stopping the slug is easy, but all the soft bits under the armor kinda just turn to a meat based jelly after a solid slug hit. I would be interested to see hi-speed camera footage of a slug hitting slanted body armor though, it could spread out the energy enough to not instantly take someone out with one shot. Not sure. $\endgroup$
    – Nick
    Jun 9 at 3:57
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There is a company called Firequest that make exotic shotgun ammunition. While the incendiary dragon's breath is more well know, they also make flechette rounds with steel darts and armor piercing rounds they claim can penetrate 1/4 steel.

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It depends on what you mean by armor piercing, and how far you want it to work from.

Armor piercing rounds generally fall into one of two categories: kinetic penetrators, and explosives.

Kinetic penetrators work by hitting a relatively small spot on the armor with a very hard object moving at high velocity. Most modern AP rounds for rifles are kinetic penetrators, utilizing a penetrator core made of steel, tungsten, or some other hard (and ideally heavy) which is either surrounded by an outer layer of some softer material, or carried down the barrel by a sabot that falls off when it leaves the muzzle. The standard alternative for a smoothbore gun is known as an Armor Piercing Fin-Stabilized Discarding-Sabot round, and is essentially a big metal arrow carried down the barrel by a sabot that falls off when it leaves the muzzle.

Explosives are a bit different. The two primary designs are High Explosive Anti-Tank (HEAT) and High Explosive Plastic (HEP, sometimes also called High Explosive Squash-Head or HESH). HEAT rounds utilize a shaped charge and a layer of metal to produce a narrow, high-velocity jet of superplastic metal which punches through traditional armor a bit like a plasma cutter (though it does not rely on any kind of thermal effect). HEP rounds, in contrast, consist of an impact trigger with a bunch of soft high explosive putty which flattens out over the surface of the target before being detonated by the impact trigger, causing a shockwave in the target that leads to spalling.

Kinetic penetrators can work for smoothbore guns, but they need a very high muzzle velocity to be effective, and therefore a rather high chamber pressure. Explosive rounds, in contrast, do all their damage with the chemical energy carried by the explosives, and thus don’t need to be moving fast and therefore do not need a high muzzle velocity or chamber pressure.

Shotguns, by their very design, do not have an especially high chamber pressure or muzzle velocity. A typical 12-gauge shotgun slug has a muzzle velocity of about 500 m/s, significantly faster than a 9x19mm round from a handgun, but significantly slower than a 7.62x51mm rifle round. That’s honestly not fast enough for a kinetic penetrator to have useful armor penetrating abilities past about 100m. However, it’s actually more than enough for an HEP or HEAT round to work reliably at a range of maybe 300m (about the same effective range as a typical assault rifle).

There are two other issues here though with a shotgun for this purpose:

  • The accuracy is horrendous. Shotgun slugs have generally poor accuracy compared to rifle rounds at equivalent ranges, and it’s even more of an issue with HEAT or HEP rounds because those are much more sensitive to the angle of impact for their reliable operation.
  • The amount of explosives you could use is significantly less than useful. Simple math indicates that a HEAT round fired from a 12-gauge will only have a penetrating power of about 125mm of traditional armor plating (not the modern composite stuff, but classic ‘block of steel’ style armor plating), and an HEP round will barely have enough energy to do anything useful. They may work against personal body armor, but are likely to be useless against a modern tank.

Now, all that said, I actually agree with you that a shotgun is a good choice of gun if you want versatility. It just isn’t really any good for reliably dealing with armor. So the proper solution is to just use a shotgun as your main weapon, and then have something else for dealing with armored targets.

If you’re going for the rule of cool, I’d probably go with the insanity that is the Triple Action Thunder. It’s a single-shot breech-loading handgun chambered in 12.7x99mm (the de-facto standard anti-materiel round among NATO countries, better known in the US as .50 BMG) that never made it past the prototype stage. It’s wholly impractical (you get one shot, and then it takes about 30-45 seconds to reload properly if you have practiced and have another round immediately at hand), but that in and of itself makes it a potentially good option for storytelling, because you can lean on that impracticality as an exploitable weakness in the character’s arsenal.

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  • A shotgun could fire better, more armor-piercing shot.
    The improvements are limited, but the HK CAWS was designed to fire tungsten pellets as well as old-fashioned shots. The increased density and hardness improved the armor-piercing characteristics slightly.
  • A shotgun could fire specialized slug-like loads.
    Ordinary slugs are short, fat rounds. But there are saboted slugs as well, and the projectile could be relatively slim and pointed, much like a modern long rod tank round.
  • A shotgun could fire shaped-charge explosive rounds.
    There are shotgun shells with explosive grenades, and the lower size limit for shaped charge rounds has been dropping for decades. Improvements in the fuse etc. might make 12-gauge shaped charges practical.
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You could use the shotgun, or a shotgun like weapon, to fire a primary shell loaded with high explosive which then on impact explodes projecting shrapnel all around.

Advantages:

  • if you overshot the shrapnel can hit your target on the back. It can be handy if the body armor is optimized for the front
  • it makes hiding behind repair less effective for your targets
  • it has a heavy psychological impact on the targets

Disadvantages

  • I suspect it violates some convention on the weapons allowed in war
  • the shrapnel projection needs to be designed to protect the person firing it from being hit
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  • $\begingroup$ The problem with explosive shotgun shells is the payload size. If it is large enough the projectile will be too heavy and getting it up to even normal shotgun shell speed will induce a huge recoil and leaving it with only standard propellant charge will mean an even slower projectile with completely different ballistics, at that time you're better off with 40mm under barrel grenade launcher $\endgroup$
    – mishan
    Jun 9 at 15:42
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INKUNZI PAW (NEOPUP), STOPPING RIFLES AND UNDER BARREL GRENADE LAUNCHERS

there are several problems with your armor-penetrating shotgun:

  1. Shotguns are made with thin barrels because they do not need to contain high-pressure cartridges.

  2. Shotguns are made with thin barrels because the payload receiving the momentum is heavy and slow (and thus does not have an enormous penetration)

  3. There are easier and better solutions to high penetration. It is always a trade-off between weight and speed with non-explosive projectiles and it is much more user-friendly if your gun does not have enormous recoil from accelerating heavy bullets to high speed under huge pressure.

  4. It is much easier and pleasant and reliable (less error-prone on the construction of the things) to create a lighter (but not too light) projectile and give it higher speed (up to a point). Your armor-penetrating shotgun is going to weigh a ton and have a kick that would probably break a wrist and a shoulder of anyone shooting the thing if the projectile is going to rely on speed/size combo for armor penetration. That will make it really unpopular for anyone who has to carry the thing for a longer amount of time and use it for more than a couple of shots.

  5. Large and light projectiles (one of the possible solutions) with high-speed experience a lot of drag. I can imagine them losing their speed (and thus penetration) and their trajectory and stability really fast. If you look at the taofledermaus videos you'll see that they are shooting at targets that are really close range and I will bet you that the slugs are extremely inaccurate and ineffective beyond the first couple of meters

That said, there is a similar thing to your design already in existence. It is not a shotgun, but a 20mm grenade launcher.

Inkunzi PAW aka Neopup - 20mm Direct-Fire Grenade Launcher

Inkunzi PAW aka Neopup - 20mm Direct-Fire Grenade Launcher

It is a 20mm grenade launcher (fires 20MM VULCAN CANNON ammunition) made for disabling armored cars stuffed with explosives attacking checkpoints. It solves the problem of recoil with a hydraulic recoil system, shoots a variety of 20mm ammo, and is accurate to a couple of hundred meters without killing your wrist and shoulder in the process. It is a beast to carry, though.

FORGOTTEN WEAPONS YOUTUBE VIDEO ON THE THING

"Double Deuce" 2-Bore Rifle: A Gunsmithing Spectacle

Forgotten weapons - "Double Deuce" 2-Bore Rifle: A Gunsmithing Spectacle

The original idea you thought about already exists and has a very limited field of use and penetration. The guns are called stopping rifles and are used for wild game hunting, where you need to stop a charging rhino or elephant. (or T-REX if it's in the movies)

The problem is the enormous weight, size, and recoil of the thing makes it almost unusable.

FORGOTTEN WEAPONS YOUTUBE VIDEO ON THE THING

UNDER-BARREL GRENADE LAUNCHER

Another thing to remember is usability. If your force is mainly using normal shotgun rounds, engineering a shotgun that will be much heavier or more mechanically complex to fire a penetrator once in a while is uneconomical and unergonomical. You're making the shotgun too heavy/complex for too little benefit.

  • If the modus operandi is to fire armor-piercing/explosive (concussion kills though armor) projectiles all the time/most of the time, you're better off with either a rifle (that fires smaller projectiles, but is easier and cheaper and lighter) or a grenade launcher/20mm cannon like inkunzi

  • if you're only firing grenades infrequently, it's easier and much more ergonomic, economic, and useful (because of payload size) to give the weapon an under-barrel grenade launcher


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