Engineering considerations for a hand-held railgun carbine [closed]

Question

The Design

The R-10 (1-2 decades pre-fall)

The SRDA's Terraforming and Colony-building Prospect is phase 2 of The Plan, started by the Theia, Tanu and the Aurea long-haul ships, which gave us access to the Ilus and New-terran systems. For mobility, industrial use and self-defense, they have heavy power-armor mechs, equipped to move cargo, carry out heavy ship repair and deal with the local fauna.

Originally built for military use, main arm for these mech's would've been the infamous R-10 Heavy Railgun. Shooting depleted uranium flechettes, it would be reminiscent of its terran predecessors, its magazine being ahead of the grip and the buttstock housed the electrical storage and switching system.

As it would have been operated by the mech driver, it would have power, control and cooling supplied directly from the suit, with the refractory super-materials used in the long-lived hall-effect engines being put to good use, with cryo-coolant being passed through channels inside the rails, like how composite resistive magnets (Florida Bitter designs) are cooled.

An iteration on this is having a secondary superconductive rail behind the main rail, which carries the current and negates the resistive heating constraints as the current only travels from the outer rail through the inner rail and to the projectile.

The K-10 (1 decade post-fall)

At the end of the first expedition into what was left of the lab, to cover an injured Kit and the space-plane trying to perform an extraction, he hauls up a discarded R-10 and fires it, injuring himself while disintegrating everything on the action-end of the rifle.

Do remember that he is a keidran. Even a gruff marine or burly mechanic guy would have trouble using one of these rifles without the mech-suit to boot. The average keidran (of which basically all are doggo-wolf breed) would usually have about 7" or so on the average human, and so it would be conceivable that a keidran marine could heft it, if it where self-contained.

But Jayden is a fox keidran, being a lot smaller, definitely had problems with a 150 pound (70ish Kg) gun. And after about 2 months of engineering and lots of sore shoulders later, created the K-10 Railgun Rifle.

The K-10 'Kitsunebi' Carbine is the first man-portable variant of the R-10, making it a rather unique all-purpose light assault weapon, with high anti-material performance. Identical to the R-10, it uses (albeit much smaller) flechettes, which come in enormous magazines, which unlike the R-10, are loaded behind the grip and trigger, coming in small cartridges of over 100 rounds.

In place of the magazine, it has the port for a standardized crystal-lattice power cell, which only store enough power for around 20-30 shots. Above the grip is the computer-aided holographic scope, which connects to the HUD of a helmet, ship computer and/or space-suit, when used.

With it's otherwise high muzzle velocity of around 2 to 4 kilometers per second and near-perfect accuracy, it doubles as a makeshift anti-material sniper rifle.

Unsurprisingly, the phase-gate ties in, as the technology needed to quickly source and sink the mass-energy equivalent of an entire mountain range is ironically very similar to that needed for a railgun. Like the R-10, the buttstock houses the electrical storage and switching system, mostly copied from the damaged phase-gate.

Unfortunately, the last and most problematic issue of this weapon (from a writers as well as an engineers perspective) is the rails and how to cool them. Since active cooling is impossible without a mech suit and all the options it gives you, the engineers (Jayden) had to get creative.

Instead of having the flechette contact the rails directly, they would have a small pad on either contact that would be vaporized as it enters the barrel. This tiny layer of plasma would bridge the gap and let current pass without wearing the rails out. (At least not any faster than conventional rifles.)

In Japanese folklore, kitsunebi (Lit. fox fires) are orbs or streaks of blue fire as methane from decomposition burns, usually appearing over marshes and wetlands. Similar to will-o'-the-wisp, they are attributed to Kitsune, magical anthropomorphic foxes of folk stories. Related to the companionship and taming of foxes in ancient Japan, they are (in some stories) portrayed as guardians and faithful lovers.

A result of the solution would be a trail of glowing blue plasma with each shot, which would look quite spectacular at night and in vacuum. As you can imagine, that is where the name came from, and I am putting up a 100 rep bounty for whoever got the reference before the explanation.

The Question

How well thought out is this weapon? Is there any glaring issues I might have with it? I don't have a single question in particular, more of whether or not any of it is flawed or flat out backwards.

Answer 1

I can't specifically answer your question per se, but I can give you some considerations that jump out to me from the description of your weapon:

Differing Ammo and Energy Capacity

100 shot magazine and a 30 shot energy cell - This isn't a good idea, for two reasons:

1. 100 isn't directly divisible by 30. From a doctrinal point of view, although not optimal - the mantra of 'Swap the magazine every 3rd energy cell' for a magazine capacity of 90 makes more sense, however even that is silly because:

2. You want a single reload. Battles are chaotic. The failure to fire drill is 'Tap, Rack, Bang' - but with 2 different sources of failure, you now have to diagnose the problem, in the field, under stress and under fire - which is bad.

Integrating both the magazine and the power cell into a single component and limiting the ammo capacity to match the capacity of the power cell makes much more sense - you are back to the futuristic equivalent of 'Tap, Rack, Bang'.

What are your combat ranges?

Traditionally, a Carbine is used as a secondary weapon system where space is limited - e.g. tankers, truck drivers, REMFs, etc. The trade-off is that the shorter barrel length means less accuracy and power at extended ranges. Case in point - the US Army switched to the 6.8 mm Ammunition for the NGSW program - this was as a result of the M4 Carbines with 5.56 ammo at the combat ranges seen in Afghanistan falling off in accuracy.

Even a carbine railgun is going to be trading accuracy for weight/compactness.

And so, you need to factor in at what distances you are expecting to engage your enemies. Related to this is

Overpenetration

Imagine most combat in your story takes place within 800 metres (double the historic fire-fight ranges) 4 KM/s is clearly overkill at this range. This does depend on what sort of armour the targets you are engaging are expected to have - but unless you have some super-fancy armour that requires that amount of velocity to punch through, then I'd say your velocity is too high - it makes more sense, for a carbine, to lower the velocity a little, increase the shot capacity of the energy cell, reduce the felt recoil (give those poor, sore shoulders a rest) to make the weapon more manageable.

However, as a suggestion: since the velocity is controlled entirely by the computer, you could have the option to increase the velocity for armoured targets.

Plasma streaks are a great way to give away your position

Having colourful streaks from your weapon sounds cool - and you might be saying 'but we use tracer ammunition in real life' - yes we do. But we also use muzzle devices (suppressors, flash Hiders, muzzle brakes, etc.) to hide the location of the shooter.

Nothing tells the enemy 'Deliver hate here' like a muzzle flash. Tracers are commonly used on high volume platforms (machine guns, cannon, etc.) where you might need to 'walk' the cone of fire onto a target, or you want to visually create a beaten zone.

A rail carbine is not likely to be full-auto and used in this manner, so these plasma flashes are going to give away your position, which strips the first 2 layers of the Survivability Onion.

Answer 2

Protect your electronics!

You said that your weapon was originally developed for military use. So, the conditions that your railgun is going to find yourself in aren't always going to be the nicest. It's going to get bumped around a lot, water and dirt are going to get into whatever little gaps there are; course, rough, irritating sand is going to get into places, your weapon may find itself in either very hot or very cold environments. You will need to make sure that whatever electronics your weapon uses aren't going to break when subjected to less-than-ideal conditions. You don't want your fancy rail-rifle to turn into a very expensive paperweight just because you dropped it one day or some dust happened to get in and cause a short circuit. Your weapon should also be able to survive years in storage.

Logistics

In addition to the fletchettes, you said that your weapon also requires a power cell. From a logistics standpoint, this is not ideal, since that would mean that your military has to worry about supplying power cells for the weapons in addition to the actual ammunition. Power cells are going to take up space, space that could be used for delivering other things. And God help anyone that can't find a replacement power cell eventhough they have a decent amount of the actual ammunition.

Moreover, the point about protecting electronics applies to your power source as well. You don't want the power cells to become worthless just because someone happened to sit on them.

Maintenance

So, you have an advanced railgun as a handheld weapon. It should be simple enough to be maintained by the average soldier. Furthermore, the more complicated your system, the more ways there are in which it can break. When it does finally break, it should be able to be repaired without too much of a hassle.