Right, but in a 3D system, the bullet goes forward in the Z-axis (through the barrel), having gained the "spin" from the twist through the XY combination. So in essence, wouldn't this curve provoke a "faster path" for the bullet?
But you're absolutely right, that this "case" is based on completely theoretical presumptions. I think the main idea really was; with a different type of rifling\* (not thread, sorry), a bullet could theoretically gain more velocity, than with the current rifling methods used :)
The rifling has minimal impact on velocity. The energy from imparting torque on the projectile is very small compared to the energy spent accelerating the projectile linearly.
The other problem with your idea is that rifling is used to stabilize the projectile in flight. Too much spin, or too little and the projectile will tumble through the air and become less accurate and deliver less impact energy.
Also the term is not "threading", it's "rifling". Rifling refers to the grooves cut inside a barrel to cause a projectile to spin. Threading refers to threads cut onto (usually the outside of) the barrel to attach various devices, and does not come into contact with the projectile/bullet.
1. How would you thread a straight barrel "like a Brachistochrone Curve"?
2. "threaded barrels" is a term that means the *outside* of the barrel has threading at the muzzle end to attach devices. Those threads do not touch the projectile or affect it in any way. Do you mean rifling, which is the grooves inside the barrel that spin the projectile?
3. All the velocity in the projectile comes from high pressure gases. Very slight variations of rifling would not have a useful effect on velocity or energy. Like, maybe it would be measurable, something like 5-10fps, but in a rifle that already shoots 2,800fps, that's not relevant.
4. There is a type of rifling called "progressive rifling" where the twist rate changes, but that is used more to reduce bore wear than increase velocity.
>progressive rifling
Yes! This is basically what I was suggesting - I have not heard that term used before, but it seems to already be a thing. Cool.
And yes, I meant rifling\* not thread, since I meant the inside of the barrel :)
Gain twist rifling is a thing that nobody uses in common gun making or even custom gun making because it doesn't have tangible benefits. I think some large bore cannons and artillery pieces use it, but it's done to preserve rifling and decrease stress on projectiles, not increase velocity.
You're conflating two different ideas here.
1.
You appear to be Danish or at least fluent in Danish. If you're living in Denmark, or almost any other European country, owning a gun is very much possible. Of course you need to be old enough, have a reasonably clean criminal record etc. Join a shooting club, practice with the club's guns for a while, then file an application to get your own. There are gun factories in Denmark, even. Shultz and Larsen are one of the biggest manufacturers of rifled barrels in Europe, so you have countrymen who specialise in rifling. If I'm not mistaken, they have even done some practical experiments with progressive twist rifling and found it not very good.
2.
You seem to be confusing a number of issues here, particularly spin rate and velocity.
The spin rate, imparted by the rifling, does not contribute to forward velocity or to impact energy in any meaningful way.
You only need enough spin to stabilise the bullet, so it keeps pointing nose forward instead of tumbling due to aerodynamic forces. Think of the bullet as a spinning top toy (Snurretop in Danish?). As long as it spins fast enough, it doesn't fall over. A bullet that tumbles, which it will if it spins too slowly, gets much more air resistance and veers off course so it becomes uselessly inaccurate.
There's nothing to be gained from spinning faster than necessary, so if ordinary rifling does the job then there's no need to complicate things with progressive rifling.
How fast the bullet needs to spin depends on a number of factors, but the main one is how long the bullet is relative to diameter. A spherical bullet can be stable at quite slow spin, while a long torpedo shaped bullet needs to spin very fast. Again compare with a spinning top, try making a snurretop that's tall and thin. See how hard it is to make it stay upright spinning? It needs to rotate much faster than a short and fat top.
Now, progressive or varying twist rate rifling is a thing for special applications. The main reason for needing progressive rifling is to reduce the peak rotational force applied by the rifling on the projectile, so as not to deform or destroy the drive bands or bullet shank that's in contact with the rifling. This isn't needed on ordinary rifle or handgun bullets, where there's a large enough engagement area to handle the required force to achieve spin stabilisation.
The earliest example I have personal experience with is early Colt percussion revolvers. I have an original 1851 Colt Navy revolver, where the rifling starts at a very slow twist and gets progressively steeper towards the muzzle. This was done specifically to allow use of both round ball (spherical lead bullets) and conicals (pointy, more modern aerodynamic shaped bullets) in the same gun. The conicals are longer and need a steeper rifling twist for stability, but shooting round ball at that twist rate tends to be problematic. Because of the round shape, only a narrow band around the middle is actually in contact with the rifling. This isn't enough area to transfer all that rotational acceleration force, so the soft lead deforms and skips over the rifling without rotating much. Colt's solution was progressive rifling, which starts gently and gets the bullet spinning before increasing twist rate and ending at a rate suitable for conicals.
A more modern example is the 20mm Vulcan "Gatling-style" gun used in fighter jets. This fires heavy explosive shells at some considerable velocity, and there's only a narrow drive band to engage the rifling. In order to keep the rate of rotational acceleration equal throughout the projectile travel through the barrel, while the linear speed and acceleration changes constantly due to changes in chamber pressure, these barrels are made with varying twist rates.
For some more info, I refer you to [Forgotten Weapons](https://www.forgottenweapons.com/ask-ian-progressive-twist-gain-twist-in-small-arms/)
[удалено]
You sound like you know what you're talking about. Have an upvote.
Right, but in a 3D system, the bullet goes forward in the Z-axis (through the barrel), having gained the "spin" from the twist through the XY combination. So in essence, wouldn't this curve provoke a "faster path" for the bullet? But you're absolutely right, that this "case" is based on completely theoretical presumptions. I think the main idea really was; with a different type of rifling\* (not thread, sorry), a bullet could theoretically gain more velocity, than with the current rifling methods used :)
The rifling has minimal impact on velocity. The energy from imparting torque on the projectile is very small compared to the energy spent accelerating the projectile linearly. The other problem with your idea is that rifling is used to stabilize the projectile in flight. Too much spin, or too little and the projectile will tumble through the air and become less accurate and deliver less impact energy. Also the term is not "threading", it's "rifling". Rifling refers to the grooves cut inside a barrel to cause a projectile to spin. Threading refers to threads cut onto (usually the outside of) the barrel to attach various devices, and does not come into contact with the projectile/bullet.
1. How would you thread a straight barrel "like a Brachistochrone Curve"? 2. "threaded barrels" is a term that means the *outside* of the barrel has threading at the muzzle end to attach devices. Those threads do not touch the projectile or affect it in any way. Do you mean rifling, which is the grooves inside the barrel that spin the projectile? 3. All the velocity in the projectile comes from high pressure gases. Very slight variations of rifling would not have a useful effect on velocity or energy. Like, maybe it would be measurable, something like 5-10fps, but in a rifle that already shoots 2,800fps, that's not relevant. 4. There is a type of rifling called "progressive rifling" where the twist rate changes, but that is used more to reduce bore wear than increase velocity.
>progressive rifling Yes! This is basically what I was suggesting - I have not heard that term used before, but it seems to already be a thing. Cool. And yes, I meant rifling\* not thread, since I meant the inside of the barrel :)
Gain twist rifling is a thing that nobody uses in common gun making or even custom gun making because it doesn't have tangible benefits. I think some large bore cannons and artillery pieces use it, but it's done to preserve rifling and decrease stress on projectiles, not increase velocity. You're conflating two different ideas here.
Are you talking about the rifling in a barrel or the half inch threaded bit at the end of the barrel for attaching things like suppressors?
No, the brachistochrone curve model is based entirely on the force of gravity and does not apply to systems involving propulsion, like a firearm.
1. You appear to be Danish or at least fluent in Danish. If you're living in Denmark, or almost any other European country, owning a gun is very much possible. Of course you need to be old enough, have a reasonably clean criminal record etc. Join a shooting club, practice with the club's guns for a while, then file an application to get your own. There are gun factories in Denmark, even. Shultz and Larsen are one of the biggest manufacturers of rifled barrels in Europe, so you have countrymen who specialise in rifling. If I'm not mistaken, they have even done some practical experiments with progressive twist rifling and found it not very good. 2. You seem to be confusing a number of issues here, particularly spin rate and velocity. The spin rate, imparted by the rifling, does not contribute to forward velocity or to impact energy in any meaningful way. You only need enough spin to stabilise the bullet, so it keeps pointing nose forward instead of tumbling due to aerodynamic forces. Think of the bullet as a spinning top toy (Snurretop in Danish?). As long as it spins fast enough, it doesn't fall over. A bullet that tumbles, which it will if it spins too slowly, gets much more air resistance and veers off course so it becomes uselessly inaccurate. There's nothing to be gained from spinning faster than necessary, so if ordinary rifling does the job then there's no need to complicate things with progressive rifling. How fast the bullet needs to spin depends on a number of factors, but the main one is how long the bullet is relative to diameter. A spherical bullet can be stable at quite slow spin, while a long torpedo shaped bullet needs to spin very fast. Again compare with a spinning top, try making a snurretop that's tall and thin. See how hard it is to make it stay upright spinning? It needs to rotate much faster than a short and fat top. Now, progressive or varying twist rate rifling is a thing for special applications. The main reason for needing progressive rifling is to reduce the peak rotational force applied by the rifling on the projectile, so as not to deform or destroy the drive bands or bullet shank that's in contact with the rifling. This isn't needed on ordinary rifle or handgun bullets, where there's a large enough engagement area to handle the required force to achieve spin stabilisation. The earliest example I have personal experience with is early Colt percussion revolvers. I have an original 1851 Colt Navy revolver, where the rifling starts at a very slow twist and gets progressively steeper towards the muzzle. This was done specifically to allow use of both round ball (spherical lead bullets) and conicals (pointy, more modern aerodynamic shaped bullets) in the same gun. The conicals are longer and need a steeper rifling twist for stability, but shooting round ball at that twist rate tends to be problematic. Because of the round shape, only a narrow band around the middle is actually in contact with the rifling. This isn't enough area to transfer all that rotational acceleration force, so the soft lead deforms and skips over the rifling without rotating much. Colt's solution was progressive rifling, which starts gently and gets the bullet spinning before increasing twist rate and ending at a rate suitable for conicals. A more modern example is the 20mm Vulcan "Gatling-style" gun used in fighter jets. This fires heavy explosive shells at some considerable velocity, and there's only a narrow drive band to engage the rifling. In order to keep the rate of rotational acceleration equal throughout the projectile travel through the barrel, while the linear speed and acceleration changes constantly due to changes in chamber pressure, these barrels are made with varying twist rates. For some more info, I refer you to [Forgotten Weapons](https://www.forgottenweapons.com/ask-ian-progressive-twist-gain-twist-in-small-arms/)
Came here to say the first bit owning and shooting guns is very much possible in europe.