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The pellet is of iron (nitrided for lubrication and corrosion resistance), or maybe aluminium would work. Either way, not lead.
When firing, the first stage of the trigger pull spins the pellet up to high RPM in the very-slightly-larger ceramic chamber, the second stage does the usual whoosh-it-through-the-barrel
thing, by whatever pneumatic machination.
Intrinsically more precise, ergonomically more accurate, environmentally friendly, less energy usage (reduced friction), cheaper (simpler to manufacture a quality barrel), more robust in the long term (no real barrel wear and tear to speak of... the barrel might be made of aluminum even - quite lightweight - with a steel shell to keep it from getting bent out of shape).
On the downside ammo is slightly more expensive and, if you run out of battery power, the pellet won't be rifled, and the effective range tanks.
Be the Flywheel
Be_20the_20Flywheel
[mitxela, Jul 04 2016]
auto-adjustable rifling
Auto-adjusting_20ri...ity_20and_20so_20on
mit zern anti-coriolis effect [not_morrison_rm, Jul 05 2016]
Spinning barrel test rig
http://nerfhaven.co...g-rifling-test-rig/
Mentioned in my anno. For Nerf darts, which are ballistically stable. [notexactly, Jul 19 2016]
Spinning tube and magnet Lenz's law demo
https://www.youtube...watch?v=CuGgNjkquxc
Proof that Lenz's law-based rotation works with homogeneous rotors (as I expected) [notexactly, Jul 19 2016]
[link]
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The spinning projectile is pushed into the smoothbore barrel by gas pressure. |
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The projectile needs to contact the bore to give a gas seal. |
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Even with lubrication, the friction will greatly reduce the spin; worse, said reduction will be inconsistent, throwing the ballistics off. |
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It's likely to be less accurate than a simple smoothbore with a rifled lead projectile. |
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The chamber - not the bore - is slightly wider than the pellet; just enough for an air-bearing effect when it's spun up. Barrel entry would be at a consistent RPM and velocity so, barring small vagaries for temperature expansion, and given consistent ammunition and a non-fouled barrel, ballistics should be fine. |
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While the barrel entry RPM is greater than exit, friction would still be less: no lands/grooves, so not as much surface to frict. And faster: no energy is wasted distorting lead off the lands and into the grooves. |
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Or a permanent magnetic field that spirals along the barrel. Probably wouldn't apply much torque. |
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Spinning the barrel however, that's genius on the same level as Be The Flywheel. <link> |
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I imagine that you could put magnets in a spiral along the barrel to make a bullet spin without needing grooves.
Interestingly, metals don't have to be magnetic to be affected by a magnetic field, but the strength of the effect varies with conductivity. It is also dependent on structure. Potentially the bullets could be optimised for the weapon, being wrapped with wire somehow. Without working it through I'm not sure what the best form would be. |
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Roughly how much energy is lost to distortion and friction in the rifled system, anyhow? |
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gah, ninja'd by mitxela. Still an interesting idea, though. |
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This concept (spin up then pneumatically inject) is sometimes bandied about for railgun projectiles. Again the projectile must contact the rails and so will lose spin to friction. |
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That is, if the rails are conventional solid conductors... |
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Grabbing something with a magnetic field takes awhile: the pre-spin system has a whole tenth of a second to do its stuff (during the first trigger pull stage), as opposed to a thousandth of a second (during barrel travel) for a magnetized barrel spiral. |
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//how much energy is lost to distortion and friction // I"m sure I've no clue. Maybe somebody with decent smoothbore and rifled .177 airguns can give a shot at pushing pellets through. |
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Ok, there's a slight problem here: the projectile won't spin. In order
to apply a torque to it, it's going to have to be something other than
a "pellet" - it'll be, by definition, an electric motor's rotor. Which, you
may have noticed, is not a homogeneous object. |
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Basically, all you have is a normal air-gun with an electric bullet pre-
heater. With batteries. |
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//Has anyone tried spinning up the barrel?// Yep. See Gatling
derivatives (e.g., Vulcan cannon). If you mean for bullet stabilization
- well, say you're trying to match a 1 in 16 inch twist at 750 fps,
which is fairly modest; that's over 33,000 rpm. Dental drill speeds
for a part which may be 30% of the weight of your gun... if
somebody tried it and survived, they'd have a helluva story to tell
afterward. |
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Like a pellet in a gauss gun, except rotational instead of linear motion. (I imagine) it's the same as an electric motor, except less efficient because there's no active magnetism on the pellet: for aluminum it has to wait until a current is inducted which then produces magnetic force to push against. Or other similar words to that effect. |
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//While the barrel entry RPM is greater than exit, friction
would still be less: no lands/grooves, so not as much
surface to frict// |
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I highly doubt it. The mass of the projectile is fairly low
compared to the friction forces you're going to be dealing
with. One option would be rotating bands as per some
tank main gun rounds - but not really doable in the sizes
you'rew probably dealing with. |
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I can't imagine this being cheaper or more robust than a
conventional rifled barrel system. Especially if the power
level you're marketting to is comparable to high powered
air rifles. They have barrel lives of 10's of 1000's of
rounds, generally the firearm is worn out or redundant
before barrel replacement anyway. |
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//Like a pellet in a gauss gun, except rotational instead of linear
motion.// |
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OK, try this: take a pellet in your hand, hold it out, and drop it.
EXCEPT: have the gravity make it spin instead of fall. That's
precisely what you are saying. |
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The way the pellet reacts to your electromagnetic field is the same
way it reacts to a gravitational field - a vector only. If you want to get
a torque couple, you need to have current flowing one way in one
part of the pellet, and the other way in the other part of the pellet.
So - the two parts of the pellet need an electrical insulator between
them. Then you need to either match the rotation of the field
generator to the rotation of the pellet, or make multiple current
paths through the pellet which can be switched to keep an
appropriate angle to the exterior field. |
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Or not. If you've a pellet within a long coil then it will shoot out of the coil, yes ? and if the pellet were outside, but next to the coil, then it would also tend to move in the direction of the coil's axis, yes ? So, if you bent the coil around to make a circle, a pellet inside the circle would spin. |
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I love this idea. It's definitely possible to get enough force
between a helical magnetic arrangement in the barrel
and a complementary magnetic set up in the projectile,
but can you make it practical. As presented I don't think
so. But, imagine an artillery piece, you could have
electromagnets arranged around the barrel describing
the ideal rifling profile. A tremendous amount of current
may be necessary to exert enough force, but only for a
fraction of a second. That sounds like a job for a big
capacitor bank. The projectile could have a piezoelectric
current, generated by the large force common in the
firing procedure. |
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I love piezoelectric. Because I love pie. Even the zoelectric ones, I think. |
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// and if the pellet were outside, but next to the coil, then it would also
tend to move in the direction of the coil's axis, yes ? // No.
The
magnetic field outside the coil (actually, a solenoid, based on your
usage) is zero (theoretically) or very small (practically) and is rejected
by a conductor placed near the field (honestly). |
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Like a coil - say a ballpoint pen spring - which is bent'round so the ends (almost) meet. Or something else that gets the pellet to spin. |
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// Or something else that gets the pellet to spin. // |
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If the pellet had a spiral grove cut into its exterior in the same direction that
the coil would impart spin then high pressure air would assist the spin. |
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/bizarrely you can get a bullet to curve if its uni-polar charged. Any net charge moving through a magnetic field causes a force. So for example, if your barrel strips electrons from the bullet as it fires, the net charge gathered would curve the bullet due to the earths magnetic field/ |
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I can tell when the coffee is working because comments like this turn into SF short stories in my head. This story would involve a space artillery duel in which the combatants use charged bodies to impart charge to and then curve the paths of the incoming projectiles. I remember an SF tale where the docking ship had lightning bolts jumping off of it as it neared the dock. Presumably there must have been some loose gas in the area to create the plasma. |
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I bet items which have been in space for a while can generate really big static electric charges from stray molecules / solar wind etc. There must be some way that the astronauts bleed that off before they go wrestling the Hubble around or they would get a big shock. |
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One can definitely attract floating cat hairs with a rubbed balloon. An interstellar analog of that maneuver should feature in the SF story. |
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Yes, good coffee. Pickled herring too. I will need to try that combo again. |
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// Has anyone tried spinning up the barrel ? // |
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*For ballistically stable projectiles (for which it is
unnecessary), which bullets and pellets
are not. |
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// Ok, there's a slight problem here: the projectile won't
spin. In order to apply a torque to it, it's going to have to
be
something other than a "pellet" - it'll be, by definition, an
electric motor's rotor. Which, you may have noticed, is
not
a homogeneous object. // |
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Furthermore, for spherical projectiles, don't you usually
want to give them backspin rather than roll? That gives
more range via the Magnus effect, and rolling for stability is
probably not helpful when the wind can't destabilize the
projectile in the first place (which, I believe, is the entire
reason bullets need to be spin-stabilized). |
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That's what paintball barrels do. I believe it's called a hop-
up. |
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// No: [link] // So you found a video with it working on a ring. Cool.
Except - it's a ring. That is, it has a hole in the middle, and an
electrical path around it, meaning that it can act as a one-turn coil,
and it's not a homogeneous conductor. Fill in the hole, and try again.
Or make some negotiation with [FlyingToaster] about perforated
projectiles which need to work with //whatever pneumatic
machination//... |
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