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Comment by chroma | Hacker News Reader

I'm rather surprised that there isn't more innovation in firearms. For example: Has anyone tried to build a rifle that fires inert pellets using a combustion chamber powered by hydrocarbons (say… propane) and an oxidizer (oxygen or nitrous oxide)? That would make ammunition much lighter and cheaper, eliminate the need for brass feeding/extracting mechanisms, and allow for "dial a velocity" by feeding different amounts of gas into the combustion chamber.

Another possibility would be to have a belt that accelerates the projectile. The "ammunition" in that case would be batteries and inert projectiles. Like a propane gun, velocity could be customized for each shot by varying the belt speed.

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Part of the issue with a design like this would be that storing compressed gases is very bulky and prone to catastrophic total failure (very bad for a weapon being abused by grunts). Gunpowder in cartridges already contains an propellant and oxidizer, and per mass you really aren't going to gain anything from going with a gas based system.

Heat management would also be a huge issue, spent casings carry away a surprisingly large amount of heat, and even then most guns are unable to sustain continuous fire rates for long. This was a serious issue with case-less ammunition designs for instance.

Yeah, anyone who's had a brass casing land down the back of their neck can attest to how much water heat they draw away from the weapon.

I also wonder how important the gas exchange caused by the mechanical cycling of the action is to cooling, as most modern rifles are pretty well sealed when in battery.

Very impractical for many reasons already mentioned here. I mean air rifles designs are very old (Napoleon famously gave order to execute any enemy soldier found with one), and they haven't caught up in any modern military.

It turns out its very practical to have fully contained ammo with casing, semi-waterproof, shockproof, can last decades easily and super cheap to make due to economies of scale. Heat dissipation from barrel friction is an unsolved problem, you can't just skip around physical constraints.

Also, having variable power isn't very practical - you want a steady point of hit for consistent fire, otherwise you would have to re-adjust gun sights/scope every single time. One of the biggest pain points of even modern air rifles - as the air pressure goes down, so does velocity of the pellets and your precision.

I think we will see sooner some sort of plasma guns than standard ammunition shot via similar ways.

There already us ammo with builtin microprocessors for adjusting trajectory etc. This coupled with some kind of guidance computer, communication with the gun sights etc would solve all kinds of problems. The sights could "project" on a screen where a bullet will land, for instance, taking into account all sorts of data, for instance where the previous shot ended up.

AFAIK both of these have been experimented with, though without much ultimate success.

For what it's worth, both ideas are represented by weapons in the old Cyberpunk 2020 rulebook so they must have been in the zeitgeist someplace:

* the Royal Enfield Ordnance Liquid Propellant Assault Rifle LPA1 http://rpg.web-mage.ca/pages/weapdesc.php?id=995

* the Malorian Arms Sliver Gun http://rpg.web-mage.ca/pages/weapdesc.php?id=824

There have been attempts to make liquid propellants work - which sound, perhaps not surprisingly, a bit like the problems associated with rocket propellants:

https://en.wikipedia.org/wiki/Bulk_loaded_liquid_propellants

[Inset obligatory 'Ignition!' reference].

I'm pretty sure the next big thing in small arms will be electronic triggers in bullpups. Bullpups' main problem is weird trigger pull, electronic trigger solves that, and also allows some more benefits (like automatic range-adjustement if you put a cheap camera and rangefinder on the weapon).

Basically when you pull the trigger rangefinder finds the range and camera takes photos one after another - waiting for the gun to get up enough so that the point that was targetted will be hit with the range that was measured.

Gunner's hands are shaking a little so he will soon get on target, and then the trigger is electronically released. You also need some timeout so that if more than for example 100 ms passes without arriving at the target it fires anyway.

The technology is there, very similar algorithms are used in smartphone cameras to harness shaking hands for higher photo resolution. The main problem is gun people distrust towards electronic in their guns.

The implementation would be fairly easy and an electronic trigger would be neat, but imo the problem with bullpups will always be the somewhat awkward reload technique that's required with that design. With an AR-15 style (or an AK) I can reload it while keeping the weapon more-or-less on the target, and dealing with malfunctions is easier because you have more space in your "shelf". With a bullpup you have to reach basically into your armpit - it's not comfortable compared to an M4.

(Again, my opinion.)

With electronic trigger you don't need impact primers, you can just put a very thin electric wire in each cartridge that gets hot when you pull the trigger and ignites the powder.

So you can make magazines that aren't possible with the traditional cartridges - like pipe magazines for strong rifle cartridges for example (hard to do with impact primers).

I'm thinking a long plastic pipe with cartridges inside that is attached paralel to the barrel. Then you just discard it with a button and put another pipe magazine under the barrel from the front. Should be fairly comfortable even with bullpups.

Additionally you can make a side port in the magazine so that you can load it with single bullets like with old wild-west rifles :)

Interesting. Didn’t think of that. I’ve always liked the advantages of the bullpup (longer barrel with shorter overall rifle relative to M4 designs). Does this mean we’d be introducing some battery requirements for operating the rifle though? That would be a flat no go for me then. Or are you saying that pulling the trigger itself would generate enough charge to operate the mechanism as you describe? Man ... turning all that stuff into plastic would sure save on weight. But I’d be a little concerned about durability.

Someone really needs to try this. I’d love to mess around with a prototype. What if you could 3D print your magazine pipes?

Maybe it would be possible to use the trigger pull energy to ignite the bullet, but it would probably make the trigger pull awful.

I'm thinking just a small battery, or even a capacitor. Charged by the recoil.

“Regenerative braking” meets “regenerative recoil”.

I love it.

I think this is just a case of what you're used to.

I grew up with bullpups and I find non-bullpup awkward to reload and harder to deal with malfunctions, and certainly more awkward to carry (American soldiers seem to have to bend their wrist when carrying their rifles where British soldiers have everything in line.)

And you don't reach into your armpit - you rotate it and then you can immediately see into the breech and manipulate it.

I’m sure with enough practice I could get used to it, and yeah I think it is a little more comfortable to carry the L85 (though I never have) since it’s shorter. How do you manipulate the bolt without taking your hand off the pistol grip though (right handed shooter)? Reaching over to the other side is horribly awkward for me. With an M4 I can take my left and just yank back on the charging handle - especially a custom one.

> How do you manipulate the bolt without taking your hand off the pistol grip though

I rotate my right hand (that's holding the pistol grip) 90 degrees to the right, then yes reach over and grab the bolt with my other hand. My hand doesn't leave the pistol grip and the butt doesn't leave my shoulder. It's never occurred to me that it might be awkward - feels very natural to me.

How do you feel about the fact that your charging handle isn't physically connected to your bolt on an AR-style rifle? I like the fact that I can directly grip my bolt and force it into or out of battery. I think on the AR you've got separate controls to pull the bolt back and to push it forward (forward assist) and neither are physically connected as they aren't reciprocating.

It may be just a lack of practice (I don’t own a bullpup rifle), but it’s always felt rough and I can’t do mag changes nearly as fast.

And great point, the charging handle not being part of the actual bolt. On the AR the forward assist is only doing work after the bolt has been “released” from the catch. A crappy charging handle can definitely cause more malfunctions. It’s also another part to clean.

Everywhere that has a law against semi-automatics that are easy to convert to machine guns will treat your electronic bullpup as a machine gun. So you won't be making a gun you can sell a semi-automatic version of to civilian gun people. Which pretty much leaves only military or law enforcement markets, which are even more biased towards simple, cheap and reliable over high-tech unless you have a really compelling benefit to offer.

Take a small drill-driver, put a wooden disk with a peg on it. Mount the drill-driver on the gun in such way that it hits the gun trigger on every rotation.

Voila - cheap semi->auto conversion that works on any semi gun and can be made in under 1 hour and 100 USD.

Or you can just buy a bump stock.

Compared to that hacking the electronic trigger is anything but easy.

A nice thing about brass cases is that they also provide a really good seal around the breach. Especially because brass is flexible enough for the thoat to expand and seal against the start of the barrel.

Any other gas based system needs to deal with keeping exploding gas from leaking out the holes through which you feed in new bullets.

The HK G11 fixes the brass problem by using a solid block of propellant stuck to the bullet.

You mean like this? https://en.wikipedia.org/wiki/Gyrojet it was featured in the 007 Movie - You only live twice, if memory serves...

Some stuff gets pretty advanced. Check out the M134D. Sure it’s 1960’s tech, but it’s still amazing.

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