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To clarify, I don't mean "whoosh kapow" laser rifles and I don't mean the handheld rocket launchers or plasma cannons fiction often tries to pass off as railguns. The weapons I'm referring to operate more like the Boeing Laser Avenger and Mass Effect weapons respectively.

The laser rifle is used on low power settings to cause skin lesions, second and first degree burns, and rapid-onset embolisms via boiling the victim's blood in small pockets. At higher settings, it can boil water inside the body to cause small, localized steam explosions to kill the target or just cut through flesh completely, amputating limbs and bisecting torsoes.

The railgun/coilgun is pretty self-explanatory. All I'm really looking for is a relatively normal rifle with a higher than normal muzzle velocity but the same muzzle energy that doesn't rely on chemical propellants.

Assuming at least a few centuries of technological progress and the advent of both antimatter power production and miniaturized fusion reactors (a question which I will likely dive into another time), could either of these modern(-ish) weapon systems be miniaturized into a handheld rifle? If so, which would be better in terms of combat effectiveness and energy efficiency?

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  • $\begingroup$ so I'm guessing you're eliminating the question f power with the last paragraph? $\endgroup$ – XenoDwarf Oct 5 '16 at 4:33
  • $\begingroup$ Yes and no. The power source needs to be portable in order to make the gun hand-held; I'm just outlining what's on the table. $\endgroup$ – Z.Schroeder Oct 5 '16 at 4:35
  • $\begingroup$ Lasers drilling or blowing up enemies is actually more realistic. By pulsing the laser, firing very high energy, very short bursts, the surface of an object can be heated extremely quickly, vaporising the surface. Wait a few milliseconds for the debris to clear, and fire again. Pulsed lasers could easily drill straight through a person, even with modern technology. $\endgroup$ – Giacomo Oct 5 '16 at 11:12
  • $\begingroup$ Reminder to close-voters... $\endgroup$ – Frostfyre Oct 5 '16 at 12:11
  • $\begingroup$ While railgun utilizes on principle of Lorentz force meaning bigger current or longer solenoid translate into powerful bullet, although laser is faster and deadlier it consumes more wattage just to pierce some reflective surfaces and don't forget it generates lot of waste heat but the future solid state laser should become standard in battle. $\endgroup$ – user6760 Oct 5 '16 at 13:19

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My guess: the choice of weapon will be determined by

  • ease of production: what weapon is easier to make and has the least strain on industrial capacity. (i personally think the railgun is easier to produce)

  • Situation: lets say the railgun is most efficient at long range (like in fields) but is rubbish in urban environments which is the laser rifles main location. You can see this in the current military as they deploy troops with weapons most likely adapted to the situation.

  • Price: The more complex the weapon the more expensive it gets. i think the laser rifle is more complex making it possibly more expensive.
  • Reliability: Which of the weapons can take the most damage before breaking, can work after being submerged in water or mud, etc etc.
  • Protection: which of the weapons is easier to defend against, is there protective clothing against any of these weapons? if protective clothing against laser shots is more common then protective clothes again rail-gun projectiles then it would be the more logical (not necessarily the most economically friendly) solution.
  • Logicistics: Are the weapons and their ammo easy to store and maintain? for Rail-gun you have to store: the gun itself, it's ammo, it's power supply but are easy to maintain for the laser rifle, the rifle and power supply have to be stored but high maintenance required

These are factors that i think must be considered in choosing the more plausible weapon. It's not an complete answer to you question but it might provide ideas.

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    $\begingroup$ I think it is a good answer, because it shows how to shape world and technology to make one or the other plausible. And shaping worlds is what this site is about. $\endgroup$ – Mołot Oct 5 '16 at 11:43
  • $\begingroup$ Agreed. In a standard, contemporary setting, Magnetic Acceleration Cannons (or M.A.C.'s) would be more reliable and easier to operate than a laser. Lasers or plasma weapons would be more likely in a more high-tech setting, since technology itself would likely make things more realistic. $\endgroup$ – Atlas the Worldbuilder Oct 6 '16 at 20:25
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From a practical military standpoint, the development of a rail/coilgun weapon is actually preferable to a laser for ground combat.

Lasers are line of sight weapons, require delicate optics and are generally energy hogs, converting as little as 20% of the input energy to laser light. (Free Electron Lasers can do better, but the issues of generating a relativistic electron beam to energize the weapon would seem to put it outside of the realm of "hand held" weapons). The soldiers using them are also limited to line of sight, can find the beam is blocked by fog, dust or smoke, and if the beam is too powerful, the air itself turns into a plasma which runs back "up the beam" to the laser emitter (meaning the laser weapon would have to operate in a pulsed mode). These issues are not as much of an issue in naval, airborne or space weapons, compared to ground combat.

Kinetic energy weapons like railguns or coilguns have fewer limitations for the soldier. He can fire through smoke and other visible obscuration. Given the massive kinetic energy of these rounds compared to ordinary bullets, he can shoot through walls and other types of cover which would stop laser light or conventional small arms rounds. And of course depending on the calibre of the weapon, he can fire a variety of rounds, including potentially smart rounds or explosive rounds, much like the XM-25 is designed to do. I suspect the evolved electric firearm will resemble the AA-12 automatic 12 gauge shotgun in concept. The soldier can fire a solid "slug" to breach cover, a flechette round filling the air with high speed darts and an explosive round to attack area targets.

enter image description here

AA-12

The main issue here is the amount of recoil the soldier will feel as the weapon is fired, so the action might be in a "soft mount" that absorbs some of the recoil force inside the stock before it reaches the soldier.

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    $\begingroup$ also the fact that you would probably need to hold a laser on a specific point to deliver the same killing energy for a time. Even if that time is "small" its still the potential to spread the killing energy over a larger area. $\endgroup$ – Marky Oct 6 '16 at 5:28
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    $\begingroup$ It's woth noting that if you want to use lasers as weapon systems within the atmosphere, you're effectively limited to certain wavelengths due to absorption /refraction properties of the air, whcih will influence how large the weapon will be. $\endgroup$ – Doomed Mind Oct 6 '16 at 8:35
  • $\begingroup$ @Marky, No. Have you ever heard of femtosecond lasers? See en.wikipedia.org/wiki/Ultrashort_pulse. However, pulse durations on the order of a microsecond might be preferred due to the fact that the damage they do extends beyond the point of impact. That's still 1/1000th of a second: by human standards that's no time at all. $\endgroup$ – Monty Wild Nov 15 '16 at 2:44
  • $\begingroup$ @MontyWild Yea, I've heard of pulsing lasers. It allows the vaporized material to move out of the way and not block incoming energy. It allows for increased application of energy, but look realistically how much energy is delivered per pulse. Again, if we have the tech to do man portable lethal damage with a one femtosecond laser pulse, we have the tech to make man portable railguns even more scary. $\endgroup$ – Marky Nov 15 '16 at 22:47
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It depends. All militaries use use a range of weapons for different means. As they say in the military, "the situation always dictates." In all honesty, chemical based projectiles are likely still the way to go in a realistic future because of their:

  1. Extremely low failure rate
  2. Ease of use
  3. Ease of repair

This is why, for nearly all of human history, despite amazing advancements, we used (and still use) variations of pointy sticks to kill each other - because they work most of the time, with little training, and are easily maintained in extreme environments.

(It could be argued that bullets are just another variation of a pointy stick. Lasers are just another form of burning people. Both carry the same hazards and advantages then as now. But that's besides the point.)

In the future, guided munitions, such as an electronically actuated bullet, are more likely, like those used in the Fifth Element, pictured below, used to hit a target behind Zorg: enter image description here

The ZF-1 used in this scene is a multi-purpose weapon, which uses multi-purpose ammunition, and is integrated with other weapon systems such as darts, flame thrower, and freeze gun, among other lethal and non-lethal uses.

But in consideration of your original question.

With laser weapons:

Pros:

  • They could easily damage unprotected flesh
  • Be safe for use in cases where hull breach (if spaceships are a consideration) is a concern
  • Only need to be large enough to have a power source and a laser diode
  • Power source could be adaptable
  • No recoil

Cons:

  • Easily refracted or scattered (by smoke or materials) by environment (weather, armor, smoke)
  • Field repair near impossible
  • War is inherently dirty, lasers need to fire through clean lenses for max effectiveness
  • Collateral damage is a great concern, due to ability to set things afire, and the inability to warn of misfire
  • If there is a Geneva Convention-like law, burning people to death could be a legal concern under an "unusual cruelty" clause

On rail guns:

Pros:

  • Can penetrate through a variety of armor
  • Not easily deflected
  • Projectile not effected atmospheric concerns

Cons:

  • Must be used in a vacuum, because recoil is either deadly in a handheld weapon...

  • Or the recoil is so violent, an auxiliary system is needed to compensate... Not amount of "technology" can account for huge amount of momentum, so there must be some system

  • The rail must be perfectly clean, otherwise the barrel would explode lethally
  • Ammunition is limited, even if it could be made very tiny

A HUGE con for both weapons:

  • Both are susceptible Susceptible to EMP

But if they were used in an infantry squad:

  • Lasers, preferred where hull penetration is a concern, or as a secondary weapon
  • Railgun, anti-infantry/light armor weapon, standard ground combat

If there is a special weapons company/platoon, such as modern militaries have, which handle mortars, explosives, and machine guns - then such a weapons section may be better suited to handling the special purpose weapons while the infantry riflemen carry reliable chemical projectile weapons.

This would allow the railgun team to emplace and give supporting fire, as well as carry the necessary equipment to deal with recoil; and a laser team to carry the batteries and lens cleaning equipment for laser.

There could be a variety of sizes of lasers/railguns much like the modern military was well - some meant to be carried on foot-patrol, and others meant for base defense or long range support.

Be sure to acknowledge that a technological advanced military must not only have the ability to kill with sticks or bare hands, but also know how to use advanced communications/navigation equipment we don't currently have available, and know how to operate if that equipment is out of commission or damaged. (Such as knowledge to repair it or ad hoc it.)

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  • $\begingroup$ worth mentioning both are only susceptible to emp while turned on. Recoil in a railgun is dependent on how fast the projectile is fired, and thanks to firearms we have really good technology for dealing with recoil. $\endgroup$ – John Nov 14 '16 at 20:34
  • $\begingroup$ @John might as well throw bricks if your weapons aren't turned on. Time to fix bayonets!!! And would EMP work so quickly, no one could react fast enough to turn their weapons off. There's also the issue of EMP disabling capacitors or batteries. $\endgroup$ – NonCreature0714 Nov 14 '16 at 20:40
  • $\begingroup$ more pro con, neither is going to replace standard firearms against infantry, but against armored targets a railgun is going to be much better than a laser, it delivers far more energy to the target for the same battery power and can be used to deliver other ordinance, like explosives. $\endgroup$ – John Nov 14 '16 at 20:40
  • $\begingroup$ but you might not turn your weapon on until you pull the trigger, depending on the design. there might not be on and off so much as firing/on or not-firing/off. $\endgroup$ – John Nov 14 '16 at 20:42
  • $\begingroup$ when I picture railguns being used I picture them being used more like bazooka or large sniper rifles. $\endgroup$ – John Nov 14 '16 at 20:43
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Well, to the best of my knowledge, the problem with both weapons system is the energy density of the energy source, meaning you either need hilariously advanced batteries to (out)compete the chemical propellant of a bullet or a hook it up to a power generator.

You seem to postulate fusion reactor, which will fit in a hand-gun, while also not melting the gun (and your hand) with the waste heat. Considering that factory hall sized attempts are still not certain to work, we are firmly in the realm of speculation/fantasy here.

If you want to go with the soft-approach, the answer will probably depend on what you want the weapons to do. Lasers are line of sight weapons, bulky (by definition their concentrating optics/mirror need to be large enough to NOT melt, while focusing the weaponized beam) who will expierence defraction and refelction in atmosphere (shorter range), your railgun slugs are slower but could be tuned to follow ballistic arches (shoot over the hill). One would also assume that railgun would experience considerable rail erosion, but if we handwave the power source, I guess, we can also handwave that.

If you want to keep it slightly more believable I would constrain Lasers/Railguns to vehicles (Tank size and up) and run with normal slug-throwers for my power armour. Maybe something like High Energy Chemistry for your slug propellant?

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There are a few factors that you need to consider with small arms nowadays.

Supply chain - or in other words, ammunition. Supplying ammo for your troops is a massive task - not just expensive in terms of sourcing raw materials and manufacturing but also the extensive infrastructure to bring the ammunition to your troops. Railguns have all the same problems that firearms today have - limited ammunition per clip, and you need to pause and reload at regular intervals. Even vehicle-mounted weapons require the arduous reloading process (although they can of course carry many more rounds). Laser weaponry would not have this issue - assuming they draw power directly from your miniaturised fusion reactors as opposed to batteries, they could effectively work forever without reload or recharge. Certainly the lifetime of the reactor would be longer than the lifetime of the weapon itself due to general wear and tear. On that topic ...

Maintenance - railguns, like conventional weapons, have moving parts. Projectiles must be moved into the barrel from the ammo clip, and fired. All of this would require mechanical movement, which needs lubrication, maintenance etc. Laser weaponry needs no such components - aside from the heat generated by firing the weapon, there would be minimal wear on the materials. No moving parts, no mechanical reloading, less wear and tear. That means a longer life, so your military can spend less on replacement weapons. Your troops also spend less time stripping their guns regularly.

Range - this has been mentioned in previous answers, and while railguns will fire projectiles that are affected by gravity (therefore increasing their range, in theory) this is not really practical for handheld firearms. Sure, a ground-mounted railgun could bombard enemies over the horizon (and artillery is used in this manner today) but the main brunt of frontline troops will be engaging at line-of-sight range. In this case laser weaponry wins, as distance will not affect their aim as lasers aren't affected by gravity. On top of this, lasers travel at the speed of light, so there's no need to lead targets. Your troops can shoot at an aircraft two miles up and will hit it instantly. No need to adjust sights for distance falloff, or wind speed and direction - just point and press.

Stealth - not something a lot of people consider, but bearing in mind how useful stealth can be (especially for snipers and commando-style units) it's still important. Railguns are incredibly loud, while laser weapons need make no sound at all as they're entirely electronic. In addition, railgun projectiles may be easy to spot (especially large ones), while lasers (contrary to most sci-fi depictions) are practically invisible (moreso if you give your stealth troops specialised lasers that pulse on and off at a high frequency, making them hard to see even in a dust cloud). The only person who could directly see the light from such a laser weapon being fired would have to be standing directly in front of it - and they'd be toast anyway.

Through all of this I've assumed you have very efficient and high-powered tech - you mentioned miniaturised fusion reactors so I'm assuming the laser weapons in question can flash-heat a target instantaneously, as opposed to having to hold the beam against a target for any length of time to do damage. The technology for this isn't out of the question, it just requires a lot of power which we can't scale down with today's technology.

The one advantage I would give to railguns is that they're much more adaptable - you could fire gas canisters, EMP charges, harpoons etc. from one. However I think for pure damage output and effectiveness my above points stand.

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    $\begingroup$ Lasers would probably not be silent: worldbuilding.stackexchange.com/questions/33112/… $\endgroup$ – Monty Wild Nov 15 '16 at 2:48
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    $\begingroup$ Also, you have not accounted for the effects of atmospheric attenuation and dispersal of lasers, but these effects are reduced with the right frequency of light and sufficiently short high-energy pulses. $\endgroup$ – Monty Wild Nov 15 '16 at 2:51
  • $\begingroup$ @MontyWild True enough about sound, I didn't consider the effect of the beam itself on the atmosphere. Still somewhat useful for stealth though as the noise will be coming from 'thin air', making it impossible to tell which direction the shot was fired from. $\endgroup$ – Cooper Nov 15 '16 at 9:34
  • $\begingroup$ Again, not so. A laser powerful enough to cause a report - and to damage a target - is going to be powerful enough to turn the air through which it passes into a glowing plasma. You'll get at least a faint glowing line leading back to the laser's source. $\endgroup$ – Monty Wild Nov 16 '16 at 0:17
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I will take the reverse position as @GijsM, to put some different point of view:

Assuming it is a futuristic mean technologically advanced, we could assume that:

  • Storage of energy is not yet an issue.
  • Production is not an issue, the cost has been optimized up to the limit where, due to massive production, cost is not a limitation.

Due to those factors, the laser weapon has been a "holy grail" of weapon engineering for long time due to its important superiority:

  • The bullet travel at light speed, making accuracy higher for moving targets. Furthermore, it is impossible to intercept.
  • Bullets do not need to be produced
  • Munition weight nearly zero (excepting battery and recharging system).
  • Not (less) affected by wind, electromagnetic fields, gravity, etc.
  • May cross some materials without resistance (windows)
  • Nearly infinite range.
  • Allows infinite / continue fire rate.

As a general comparison, if technology is not a limitation, laser is much more effective.

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  • $\begingroup$ I'm not sure all of your listed advantages are true. You mention windows as being crossed "without resistance" but in most cases there will be partial reflection of the laser light, which will reduce the energy reaching the target. Similarly, infinite range would only happen in a vacuum, gasses would scatter and absorb the laser energy. Also I suspect that generating high energy laser light would also generate a lot of heat, which would limit the ability for continuous fire. $\endgroup$ – Steve Bird Oct 6 '16 at 8:32
  • $\begingroup$ You have to put those affirmations in the context: we are comparing bullets against laser: - Range of bullet: Precision lost after a few hundred meters. Energy decay after a few km. - Range of laser: Precision in air still very precise after several kilometers. Energy is mostly maintained over hundreds of kilometers. - Bullet: Will not cross a blinded glass. - Laser: Will cross and be still mortal after. $\endgroup$ – Adrian Maire Oct 6 '16 at 9:04
  • $\begingroup$ For your last affirmation, energy lost of a laser depends on the quality of the fabrication. Furthermore, is more important the laser density than the absolute energy (a very thin laser can still cut). Heating is also a problem for bullets weapons, but much more difficult to reduce there. $\endgroup$ – Adrian Maire Oct 6 '16 at 9:04
  • $\begingroup$ @adrian yes and no, a laser needs to produce a lot more heat for the same effect on the target. the laser HAS to be hotter than you want to make the target. $\endgroup$ – John Nov 14 '16 at 20:49
  • $\begingroup$ interception in not an issue for even modern firearms and munition weight is basically battery weight for railguns and lasers and will much higher for lasers even when you add in the slug weight for railguns. bullets pass through lots of materials with little resistance, not just transparent ones. lastly heating a target is just less destructive for the same unit energy. $\endgroup$ – John Nov 14 '16 at 21:20
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Rail-gun/slug based tech 100%

I'm ignoring the fact that you have man portable lasers that can bisect things at will; if that’s the case you're never going to have infantry combat at all (and rail guns will effectively operate identically at that power level too.)

The advantages of throwing something physical totally outweigh the advantages of a laser. (It’s also traditional for humans.) There are going to be a lot of opinion based reasoning and you can propose situations for both sides and then counter them.

For example: Smoke rendering lasers useless, counter; if the laser is that powerful, it will ignore smoke/and or shoot a different wavelength of laser. Urban combat being poor for low fire rate slug throwers, counter; mini-gun - The loud bangs of slug throwers are demoralizing to enemies, counter; the beams of light from out of the darkness seeking to burn your eyeballs out of your skull are demoralizing to enemies.

The biggest point FOR slug based guns is actually the basic problem with lasers; you have to hold the laser on target, while for a slug based weapon you only have to get the weapon on target at the same moment you pull the trigger.

Weapons are all about imparting a lethal amount of energy to someone you want to go away. Slugs carry this energy in mass and velocity, and impart it by destructively dumping this energy into the soft tissues of the other guy. Lasers impart this energy by heating a point; the more energy you want to impart the longer you have to hold it on that point. If you stray even a little bit, you lose a massive amount of destructive potential because you are spreading your energy around rather then focusing it.

I'm sure you can google the amount of force it takes for an object (bullet) to penetrate flesh, but don't assume a laser outputting the same energy held by a person will ever do the same kind of damage. It will cause burns sure, but you and the other guy are not going to be standing still and that same amount of energy will get spread around.

Lasers might make sense as a vehicle mounted weapon where you CAN get the “cut everything in half” feeling because they're bringing their power-plants with them, but at the same time you’ll have the Gauss based Vulcan on the other side.

Ultimately you need to decide what tech level your at; once you start getting to star trek levels of personal power potential [pew pew pew], infantry make almost no sense (unless you get equal super-tech armors). Lasers start to get advantages once they get hit-scan-kill abilities because they have no ballistics and start penetrating matter like rail-guns will, but until that point, all you're doing is putting burn marks into things.

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Both

If you posit that you have solved all the relevant technical problems for creating rifle-sized versions of both of these weapons, you're already in the space where you can determine what the in-world advantages and disadvantages of each one is. Given the number of constraints given above, it would be easy to decide that a given squad would carry one or more of each weapon type.

To wit: Assuming hugely dense energy sources, lasers effectively have near-unlimited ammunition, and are unlikely to cause significant collateral damage. They are also likely cheap to produce and maintain, as they have few moving parts. This sounds ideal for the futuristic infanteer, who will be used to take and hold strategic assets and conduct house-to-house clearing of same. One or two squad members might carry the more expensive and specialized railgun, for use in specific situations.

For terror troops, raiders, and other special forces, the railgun will likely be more useable. The cost and maintenance will matter much less, since they will be deployed on a small scale, and can use special ammunition tailored to the mission. Collateral damage is an asset for many of these mission types.

Much like militaries make use of many different chemically-powered weapons now, in order to take advantage of the varying effects of those different weapons, so too will the rail rifle and lasgun become a part of a larger arsenal.

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there is an online calculator for kinetic weapons and lasers, both are however in a vacuum. http://www.5596.org/cgi-bin/kinetic.php

http://www.5596.org/cgi-bin/laser.php

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Various good answers here, but I'll point out two advantages of laser weapons that haven't been mentioned.

  1. Lasers are much more flexible as a weapon. With a rail gun, what you will end up with generally is a high powered rifle. With a laser, on an individual device you have the potential to have a variety of firing modes for the situation. Need a shotgun? Turn up the dispersion and tune up the capacitors. Need suppression fire? Switch to continuous beam and attach a big heatsink. Want to blind enemy sensors? Lower power output. You can have it all in one package.

  2. Lasers are a lot easier to aim. With a rail gun, you basically have to align the entire assembly with the target. With a laser, aiming can be accomplished by turning the final lens. What this means in an infantry weapon is that a rail gun is limited by the abilities of the human holding it, whereas you can easily imagine building in auto aim capabilities to a laser rifle. Stick a camera and a computer on and your laser rifle user needs only to aim in the general direction of a target, pull the trigger, and bam, perfect headshots every time.

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Your railgun, unless it has some massive detriment, is going to be the winner in this matchup. You have more versatility over the laser in terms of ammunition and loadout, and you don't have to hold your shot on target.

That said, a laser weapon might have a specific valuable role, such as a sniper's weapon (if the laser beam doesn't diffuse over a long distance, it will be more accurate than a kinetic round).

The real question then becomes is the railgun better than a traditional firearm?

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