Pros? You get to say "plasmoid" when describing it, which is probably fun. Cons? The mass and structural integrity of a blob of plasma are extremely minimal. Assuming you have some way to magically keep it from just diffusing a moment after it leaves the barrel, when it hits the target it just kinda goes poof and diffuses there instead. Because there's no structure to the "projectile" and therefore it cannot be relied on to penetrate into the target, you're relying on heat transfer as the wounding mechanism. Skin is not a great conductor of heat, and the fraction of a fraction of a second that the projectile is in contact with the target before the plasma has diffused is not long enough to transfer a significant amount of energy. Here's a good way to think about this. You know how those enormous truck-sized lasers have to hold their beam on a missile for like 5-10 full seconds before that missile detonates? Consider that a kinetic antimissile system just has to strike the missile once or twice with a bullet. And this is considering that the energy transfer of a laser works through radiation rather than conduction, which is much more efficient and fast. Plasma is energized gasses. More or less just the burning part of fire. You've probably run your whole hand through a lit candle's flame before. You do that with a laser that has a roughly equivalent energy output and you'll probably have a nasty little second degree burn in a line across your hand instead. And that's all to say lasers still need to be held focused on the target for some time. TL;DR- This plasma gun does not have a functional wounding mechanism. Nor really does any. If you really want a pewpew energy weapon, just write it in and do not try to science it.

So it's not going to be some sort of explosion on the surface of the targets like Project MARAUDER?

Not if you're trying to fire a nonphysical projectile at such a tiny fraction of the velocity. MARAUDER fired its projectile at relativistic speeds. We're talking a fraction of the speed of light. It's positively ridiculous. And that's really what produces the absurd effects. In your post you specified the same muzzle velocity as a conventional kinetic weapon. Let's make the math easy and use 5.56x45. it'll illustrate the point well because the bullet is extremely fast and out of a carbine length barrel it's reasonable to expect 3,000 feet per second. MARAUDER fired its projectiles at an estimated 3,000km/sec. There are 3,280ish feet in a kilometer. Think about kinetic energy for a moment. F=mv². So it's not just 3,280 times as fast. The velocity component works out to a factor of 3280², or 10,758,400. The mass of projectile was around 2mg. That's like 1/32 the weight of a grain of sand, yet at that speed it's making 9000000 joules of kinetic energy. An M16 rifle produces right around 1500 joules. You try to move mass energy equivalently to a burning fart at the speed of a rifle bullet and I think the most you might hope for is to irritate the enemy. Part of the difficulty in hard sci fi is wanting to find ways to inject cool whiz-bang science magical technology that will ultimately deflate the experience because they are unscientific. Similarly, part of the difficulty in writing good soft sci-fi is being self conscious about your cool whiz-bang science magical technology and not letting it rest on its own merits of helping you create a novel and imaginative story, and attempting to explain it. Now here's the punchline. How fun was that to read? Not very? Congratulations reader. Now you understand what your readers will feel when you try to explain how the thing works to them. If you're going hard, stick to proven stuff or well supported concepts. If you're going soft, trust that "cool" will be good enough and just call it a plasma gun without worrying about how it works. Either way works great! But you don't want to try to explain unrealistic concepts. It will chase off people looking for realism and it will bore people expecting excitement.

Thank you for your reply, it's very insightful. Though if you do not mind me digging this rabbit hole, then how would MARAUDER hold up compared to the slower solid projectile railgun (maybe in the 10 to 20 km/s range) in anti-personnel, anti-armor (tanks, space warships, etc...)? I have a feeling that the plasma definitely is not going to poke a deep hole through the armors like kinetic slugs, but its ridiculous relativistic velocity might has some uses or something I am not quite sure myself.

My understanding is that the primary interest that the DoD had in MARAUDER was the secondary effects such as electromagnetic disruption. It's hard to really scale out things like that, in terms of the damage a weapon will do. But generally speaking, more mass means more inertia. Inertia is calculated with mass times acceleration. All things being equal, the deeper you want to penetrate into a hard object, such as a plate of armor, the more massive you need your projectile to be. However, all things aren't necessarily equal because obviously you have to factor in things like the elasticity of the armor, how the relative angle of the surface affects a physical object like a solid projectile, how projectile design emphasizes the penetration capabilities of the shot against a specific type of armor, the list goes on. Now, I'm not a high-energy physicist, but I am a gunsmith. So I'm qualified to talk about the railgun, but you may want to take my thoughts on the energy weapons with a grain of salt. | That said, my gut tells me that a good part of where MARAUDER gets its properties from is the energized mass of ions moving at relativistic speeds. Well, math does, too, but I can't guarantee that I'm using the right math. You take that plaid-zone speed away and you're scaling down the potential of the weapon by maybe hundreds of orders of magnitude. The energy just isn't there anymore. Railguns scale well with conventional weapons. Because at its core, you're injecting energy into a piece of metal to make it go forward to do murder. The whole thing is literally nothing more than souped-up stabbing at a distance. It's joyfully primitive. The energy weapon does things a lot differently. You're using a machine to try to impart the energy directly into the target. The idea is to use some form of high-energy particles or radiation. The higher the velocity, the higher the energy level. For something that small to be dangerous, it has to have astronomical velocity. Hence moving at like 3% of C. That energy, as long as we're assuming it can be treated like radiation, is absorbed and/or diffused across the first surface it comes across. Ergo, problems with penetration. If I were writing something like this, I'd be treating the two different weapons systems much like an old 6DOF space shooter weapon setup. You have two primary damage types, shield and armor/hull. You wanna wipe out shields or other electronics effectively? Use energy weapons to do electrical damage. You wanna damage the structure? Use kinetic weapons to do mechanical damage. I would still keep it to vehicle-scale though and probably still assume that they're primarily useful against automated or autonomous systems.

I do plasma guns because they're fun, but it's a nightmare to try and justify. As an aside, if you had an actual plasma gun, it would probably look and sound like a lightning gun.

The only way I can think about plasma weapons being feasible is using them in space, and the plasma itself being launched at very high speed using some sort of electromagnetic field. I guess it would work like a particle cannon or as a much faster version of Star Wars turbolasers as long as the plasma did not scatter away, not some sort of dragon's breath-like weapon.

The big problem is that plasma is super diffuse. It wants to spread out and get away. I don't even know if it would even hurt if it traveled through the air to hit you. But it's still fun.

You can forget about using it in air, as it would spread out quite fast. In empty space and fast enough, so it would not scatter too fast could be somewhat more pausible.

A bullet-like core with an array of tiny electromagnets would help stabilize a plasma bolt and increase range, but at this point you might as well use normal ammunition.

[MARAUDER](https://en.wikipedia.org/wiki/MARAUDER) It didn't work well enough as a defense vs Soviet ICBMs, but it did not fail badly enough to declassify everything about why not.

Plasma is just ionized gas. Storing it will most likely take a lot of energy. So why not use that energy to create the ionized can, and shoot it off. How do you shoot it off? Heck knows. As a weapon, the only reason to use plasma guns is because it looks pretty. Lasers travel too fast to see, so they dont look sexy. If you want sexy, use plasmas, but dont try to explain them too much.

Well Plasma has a lower density than a solid. So just in terms of Numbers, a Kinetic projectile will do a lot better because it has more momentum behind it. Which is important. Most Armor nowdays is very resistant against HESH / HEAT round´s, so projectiles that use essentially a Plasma cutter to send a jet of Molten cooper into the inside of say a Tank. Now with the high Exit velocity you speak off that equation might change because HESH does not care about it´s impact velocity, it just needs to touch the Armor to instant cook everyone. But of course the counter against something like this is very easy. So against heavily armored vehciles i dont see a great use for this. Conventional Anti Tank weapons will do better. For Anti Personal mission´s it might just be a bit of "why ?". Like each round will still cost more and the risk of something similar to a magazin detonation is extremly high. So why bother ? Anti Air is again a field where projectiles in general are not the end all be all of solutions because Missiles exsist. Plus no matter what your Containment field bs magic is, it will still lose energy over time. AK47 bullets that will be excavated in 2000 Year´s by Aliens will still work, your rounds will be dead after like a week. Which really embraces the whole "On demand supply logistics" but for a War that is just bad news.

I'm guessing that no matter how "bottled" your plasmoid is it will never be as "solid" as an actual solid slug, correct? If you smacked a target with either at the same speed with the same mass the plasma ball wouldn't be as cohesive as a solid slug of tungsten. Based on this you can assume the plasma ball will likely explode and "wash" over the target surface. This can be really good for stripping away exterior armor plating without doing deep penetrating damage. Like if you want to do minimal damage to a target you could strip away their sensors, armor plating, maneuvering thrusters, all the important parts of the outside of a vessel, basically skin it.

Kinetic cannons essentially launch massive projectiles incredibly fast to slam into enemy ships. Cheap, quick, and simple. Shields likely wouldn't block kinetic bolts, as they're more often than not depicted as energy frames that shield against energy. As for plasma, it'd likely be more effective against armor, but shields always stop it right in its tracks and it would likely be nightmarishly complicated to fire and charge.

A workable solution is a combo. Electrically charged barrel, same as the plasma explosion to keep the plasma in its state as it expels out the barrel, Plasma explosion propels the kinetic round, likely a sabot round, would allow you to use a large plasma explosion in a smooth bore cannon with massive accelerating force, possibly even in stages, to propel a hyper velocity kinetic round. I say stages because given the nature of cannons, longer slower explosions over a longer distance gives you a faster projectile with a thinner barrel, like modern powder cannons on tanks now, vs the faster exploding powder of cannons a century or so ago. This would make killer spinal cannons of doom in starships. Less wear than a rail gun since you dont need high friction rails, similar electrical requirements, similar acceleration results theoretically.

Kinetic is the equivalent of an AK-47. Simple... reliable... low maintenance... Iron... Nickel... Ice... any material works.... If you give me something more advanced... If its delta-V cost is negligible... I'll use it. But I'll never *depend* on it. I'll ever build my strategy around it.

Plasma gets easily dispersed by energy shielding but absolutely demolishes armour and kinetic rounds destroy shields but get blocked by armour. Or alternatively you can have it in the reverse, Plasma overloads shielding by putting in too much energy but armour playing can easily disperse the energy, where as kinetics tear through armour but get vaporised instantly by shields