22 replies to this topic

[Gym]

I searched "rifled barrels" before writing this and found no ideas along the lines of this topic so I hope this is more than another opportunity to discuss how awful it is to rifle barrels for Nerf purposes. My idea is not to rifle barrels, but to create the spin effect by rotating the barrel itself. If the barrel is rotating with a dart inside it makes sense that the dart, when exiting the barrel, would be rotating (similar to the effect of rifling on a bullet).

Now the main opposition to the application of rifling to Nerf that I have found consists of a few criticisms:
1. Forward energy is partially converted into spinning energy, resulting in a loss of range.
2. Nerf darts experience stability and balance based on weight distribution.
3. Nerf blasters do not create enough pressure compared to a firearm.

In response based on the rotating barrel idea:
1. The projectile fired from a rifled barrel is probably slowed down by friction from the grooves and the torque. With a groove-less barrel that rotates the friction from rifling is no longer an issue. Also, doesn't the spin actually result in less air resistance? (think of throwing a football)

2. In the case of spinning objects, don't they become balanced around the central axis of motion (that whole centripetal force thing), making the weight distribution of a foam dart irrelevant?

3. Based on the above, potentially flawed, logic how much of a spin is necessary to create an accurate and long-distance Nerf dart?

It has been a few years since high school physics, but if I am wrong I'm sure someone will point it out.

My hypothesis is that rotational energy, when produced by a rotating barrel rather than friction from a rifled barrel, will not detract from forward energy; and that at some speed of rotation the dart becomes balanced.

I write this because I don't have the means or the time to pursue it, but some of you do. There are any number of ways to spin a barrel and I'm sure if anyone is interested in this idea the best method could be perfected. So throw out any prejudices against rifled barrels and consider the physics and the mechanics of this new idea and suggest why it could or could not work.

[boisie]

Do it then, and show us some results.

[Galaxy613]

2. In the case of spinning objects, don't they become balanced around the central axis of motion (that whole centripetal force thing), making the weight distribution of a foam dart irrelevant?

Weight distribution, I would think, would be even MORE cruical if the dart was spinning. If the weight was NOT directly in the middle of the foam, then while it rotates one side will be heavier than the other, causing it to fish tail easier than normal.

Honestly, we can debate and argue all we want. Go out and get results. The hardest part will be getting the barrel to spin at a steady rate and still connected to the power source. Most likely brass so you have nest the brass barrel into a larger/smaller sized brass that is connected to the power source. The barrel will be able to spin around easily..

[bpso86]

In response based on the rotating barrel idea:
1. The projectile fired from a rifled barrel is probably slowed down by friction from the grooves and the torque. With a groove-less barrel that rotates the friction from rifling is no longer an issue. Also, doesn't the spin actually result in less air resistance? (think of throwing a football)

Spinning an object such as a nerf dart or a football doesn't actually result in less air resistance. You've still got the same amount of "wetted" area (the area that the air flow sees) which creates drag. Now, if we're talking about a rotating cylinder which is positioned perpendicular to the flow, then it would create lift while rotating, but our darts are being fired into the flow and therefore that doesn't matter. You will have the same amount of friction in your spinning barrel that you do in a regular barrel.

2. In the case of spinning objects, don't they become balanced around the central axis of motion (that whole centripetal force thing), making the weight distribution of a foam dart irrelevant?

Technically, yes... spin does stabilize projectiles, but there is only so much that it can do. In terms of ballistics, if the force that the spin generates isn't enough to overcome the force that the air pressure behind the projectile generates upon the center of mass of the projectile, then it won't help. If you've got a weight at the back end of a dart and fire it, the force from the air pushing the end of the dart will be much greater than the rotational force from the spin, and therefore it will want to push the back of the dart forward, causing a "tumble". Think about what would happen if you tried to fire just a piece of foam with no weight through a rifled barrel. Do you think it would remain in a steady flight path even with no weight up front? The drag that the dart encounters will want to flip it around if there is no weight in front to counteract it, and spin won't do anything to alleviate these effects. You have to understand that spin stabilization works best in environments where other earth forces don't matter (Space, for instance), and here on Earth the aerodynamic forces of drag and viscous friction along with gravity are much more prevalent.

3. Based on the above, potentially flawed, logic how much of a spin is necessary to create an accurate and long-distance Nerf dart?

None. In all honesty, if you've got weight up front then you don't need spin. If you're real intent on seeing if it would work, though... grab a physics book, look up the equations for rotational inertia/momentum and rotational forces and run some numbers.

My hypothesis is that rotational energy, when produced by a rotating barrel rather than friction from a rifled barrel, will not detract from forward energy; and that at some speed of rotation the dart becomes balanced.

Once again here, we have a basic lesson in Physics. Newton's First Law: A body at rest (or moving) will stay at rest (or moving) unless acted on by an outside force. If you've got your dart spinning at a certain velocity along with your barrel, when you fire the gun and introduce a huge force to propel the dart out of the barrel it will lose almost all (if not all) of that rotational energy since there is nothing to keep it rotating once it is released. Since the only thing keeping the dart rotating in the first place is the friction between the dart and the barrel, it will eject from the barrel and will not continue to spin. Once you fire the dart, it wants to get out of the barrel as quickly as possible, which puts it in a straight line out of the barrel. That spin can only be kept if there is something to keep the dart spinning as it moves through the barrel, and this can only happen if you've got a REALLY high friction force between the dart and the barrel, at which point you're effectively eliminating the propulsion effects from the air pressure.

So, looking at it from a physics/mechanics point of view: No, I still don't think it would work.

But don't let me stop you.

[cheesypiza001]

You did say you were originally looking for something like this:

NHQ - Rifled Petg

Edited by cheesypiza001, 03 December 2008 - 05:40 PM.

[imaseoulman]

You're spot on with all of your physics, but either I'm misunderstanding something with the next part...or...

Once again here, we have a basic lesson in Physics. Newton's First Law: A body at rest (or moving) will stay at rest (or moving) unless acted on by an outside force. If you've got your dart spinning at a certain velocity along with your barrel, when you fire the gun and introduce a huge force to propel the dart out of the barrel it will lose almost all (if not all) of that rotational energy since there is nothing to keep it rotating once it is released. Since the only thing keeping the dart rotating in the first place is the friction between the dart and the barrel, it will eject from the barrel and will not continue to spin. Once you fire the dart, it wants to get out of the barrel as quickly as possible, which puts it in a straight line out of the barrel. That spin can only be kept if there is something to keep the dart spinning as it moves through the barrel, and this can only happen if you've got a REALLY high friction force between the dart and the barrel, at which point you're effectively eliminating the propulsion effects from the air pressure.

So, a spinning object will continue to spin until an outside force acting on it causes it stop spinning (according to Newton's first law). The only force added to the dart is the expanding air and that pushes the dart forward (out of the barrel). What force is causing the dart to stop spinning?

[bpso86]

My point was that friction causes it to spin in the first place, so friction would have to be higher than the force generated by the air flow to keep it spinning at a useful velocity.

Maybe I should explain it in terms of resultant forces. The direction of the friction force with no air behind the dart is along the skin of the dart ("around" it, not going out the barrel). When you introduce a very large force from the back, friction is now acting in that same direction, along with a huge force vector pointing out of the barrel. When you resolve these forces, you'll get a very small change in angle from the axis of the barrel, which would give you spin. I did say in that paragraph that it would lose almost all (if not all) of its rotation. There would still be some there, depending on the strength of the gun this is being used on, but not enough to induce the spin required to keep it stabilized.

I apologize if I was unclear in that respect.

[Split]

Gyroscopic stabilization is used to stabilize a projectile that is not aerodynamically stable. You do not have to add rotation to a projectile that already is inherently stable (as your darts should be since they are front-weighted).

Anyway, theoretically, I'll add some actual comments:
Criticisms:
1: True. The amount of lost "forward" energy/momentum is going to correlate to how tight the spin is. It's virtually negligible in real guns due to extremely high velocities, and very accurate and minimal variation in rifling, as well as massive engineering solutions to the entire problem.

2: See quote

3: Enough pressure to accomplish what goal? To create spin via rifling? Probably not. This is very linked to number 1.

Responses:
1: It's not torque; it's only the grooves. The grooves (like an object moving around a curve) convert "forward" momentum into angular momentum.
The spin doesn't result in less air resistance, just less drag. Without the spinning, the football would have an immense drag factor from its width in the center, and would lose its accuracy (see quote).

2: See quote. You went in the wrong direction here. The weight distribution doesn't hurt the effects of gyroscopic stabilization - it negates the need for them.

3: Based on 2 - none.

If, for some reason, you didn't weight your darts, and you wanted them to be semi-accurate (streamlines, possibly?) to a very short range, you could go through all of the work of a rotating barrel, and that would solve the criticisms 1 and 3. A simple plan to make that happen would be along the lines of a wheel on a motor that turns a piece of brass that's nested over another piece. The advantage of shooting blanks at people? No clue.

Oh wait, you can't actually do this? Kthxbai. It would work; it would be redundant.

Edited by Splitlip, 03 December 2008 - 08:30 PM.

[bpso86]

The spin doesn't result in less air resistance, just less drag. Without the spinning, the football would have an immense drag factor from its width in the center, and would lose its accuracy (see quote).

I don't mean to be rude, but you're contradicting yourself here. You're saying the spin doesn't result in less air resistance, but it does result in less drag. Aerodynamic drag is mainly caused by air resistance, so you can't drop drag without dropping air resistance (unless we're talking about induced drag, but that deals with lift and we don't care about lift right now). The football would have more drag without spinning, but only if it is facing the flow field lengthwise. I was referring to the football sitting in a flow field in the same direction, both with spin and without. If it were facing a flow field on its axis of rotation with spin and then without, there would be no difference in drag.

Once again, not trying to be rude or start an argument, but I'm just trying to clear up some apparent misconceptions.

[ShadowFire]

for more friction between the barrel and the dart, you could find a tight fitting barrel that is grooved like a LS barrel. I also notice that even with a dart that has three BB's in the tip, it almost tumbles just as it exits the barrel of a powerful airgun. (I wish I had a high speed camera to see in slowmo)


when doing a ballistics lab for physics is when I got three classmates into Nerf

[CaptainSlug]

This thread is pretty pointless.
If you make your darts properly then pre-spinning them when they are fired will gain you absolutely nothing.
That's really all there is to it.
No amount of spin will make your darts any more accurate because they don't have enough velocity or mass to overcome drift from a minor breeze. You can be fairly accurate UP TO 100 feet, but anything beyond that simply isn't possible because of the nature of the darts themselves.

I also notice that even with a dart that has three BB's in the tip, it almost tumbles just as it exits the barrel of a powerful airgun. (I wish I had a high speed camera to see in slowmo)

That's because the air escaping behind the dart as it leaves the tip of the barrel is creating turbulence that destabilizes the dart momentarily. If the problem affects your accuracy you may have to drill a few ports just behind the tip of the barrel. This will allow the bulk of the excess pressure to vent away from dart.

Edited by CaptainSlug, 04 December 2008 - 01:56 AM.

[ShadowFire]

I don't mind the momentary unstability because it provides a bit of deceleration to the major initial velocity without decreasing accuracy too much. A 200ft range is good enough for me.
Back on topic; even at low rpm, enough friction can destroy rubber. (if you have one of those rock tumbler you know what I'm talking about)

[Blasphemy]

I was surprised not to see the factor of the generally imperfect surface of all darts mentioned in this thread. the "rough" surface of all darts causes inconsistencies when you try to induce spinning on it using grooves which may or may not make contact with different elements of the surface. These are not actual firearm rounds, they are not crafted to be that smooth on the exterior, nor can they be.

As far as I know, results from rifled barrels have typically been a mixed bag, some results show improvement in accuracy and range by a decent amount, but others show near average or slightly below average performance.

Who knows though, If you can find an easy way to rifle a barrel really well and find darts with a very smooth surface, we're talking even smoother than stock dart-smooth, and do everything else right including weighting it evenly and adding a perfect half-dome, then you might see that same increase reported by others except more consistently. But until that day the general opinion by most nerfers is that it is not worth it.

[Doom]

If you want to reduce the effects of drag, look into more aerodynamic dart shapes. A flat cylinder with the aspect ratio of a Nerf dart has a coefficient of drag of about 0.82. Round off the front of the dart and you're down to about 0.2. Data is from here. Most Nerf darts and stefans are somewhere in between but not as rounded off as they should be. The increase in range won't scale like linearly with the coefficients of drag, but it'll definitely exist.

Because Nerf darts aren't perfectly smooth I don't expect those figures to be completely accurate, so take them as approximate at best.

The other variable we can control in drag force is cross sectional area. There's not much we can do about that aside from using smaller stefans. 3/8 inch stefans are not too common but theoretically they could perform better. I wouldn't use them myself because they're very non-standard.

Edited by Doom, 05 December 2008 - 02:59 PM.

[Gym]

No amount of spin will make your darts any more accurate because they don't have enough velocity or mass to overcome drift from a minor breeze. You can be fairly accurate UP TO 100 feet, but anything beyond that simply isn't possible because of the nature of the darts themselves.

Although the topic is "pointless" I should mention that some Nerf Wars take place indoors with stock or modified darts (not always stefans). This is the case for me. I should have clarified this initially, but I am not interested in creating significant accuracy above 100' and I'm not worried about a light breeze. I thought about this topic after observing the highly inaccurate flight pattern of modified tagger darts from a nested brass modded BBBB. The idea crossed my mind that maybe spinning would help, as it does with a football (as I suggested above). This topic is also not meant to have any application to blasters that have a short range (less than 50' for example), but more for the long-distance rifle type of blasters. I am intersted in the application of this idea for those of us who play indoors year-round with or without stefans.

[hereticorp]

Although the topic is "pointless" I should mention that some Nerf Wars take place indoors with stock or modified darts (not always stefans). This is the case for me. I should have clarified this initially, but I am not interested in creating significant accuracy above 100' and I'm not worried about a light breeze. I thought about this topic after observing the highly inaccurate flight pattern of modified tagger darts from a nested brass modded BBBB. The idea crossed my mind that maybe spinning would help, as it does with a football (as I suggested above). This topic is also not meant to have any application to blasters that have a short range (less than 50' for example), but more for the long-distance rifle type of blasters. I am intersted in the application of this idea for those of us who play indoors year-round with or without stefans.

By it's very nature, Indoor nerf doesn't really use long range guns. To most people, indoor nerf is city or office combat, not an indoor soccer field or gym.

So long distance really doesn't go with indoor nerf.

And you'll get a much better effect out of adding a little more weight to a tagger than you will from any sort of spinning.

[Gym]

By it's very nature, Indoor nerf doesn't really use long range guns. To most people, indoor nerf is city or office combat, not an indoor soccer field or gym.

So long distance really doesn't go with indoor nerf.

That may be true for many indoor players, but I play in a church with a few long hallways (between 50' and 100' more or less) and a couple large rooms (one is a basketball court-size gym). The reality is that while many people who play Nerf may play outside or informally inside (in offices and such), there are a number of players who play large coordinated indoor Nerf Wars in large buildings and it is just as important to consider this environment as any other when developing new ideas.

I don't think this idea is useful for everyone who plays indoors, even those in similar buildings to mine, but I think there is a niche where it fits. It could be that the benefits of using a spinning barrel are marginal compared to the time and effort of production, but the only way to know is to try. If the idea is a success or a huge failure I wanted to give those interested in this sort of thing the opportunity to find out sooner rather than later.

[hereticorp]

That may be true for many indoor players, but I play in a church with a few long hallways (between 50' and 100' more or less) and a couple large rooms (one is a basketball court-size gym). The reality is that while many people who play Nerf may play outside or informally inside (in offices and such), there are a number of players who play large coordinated indoor Nerf Wars in large buildings and it is just as important to consider this environment as any other when developing new ideas.

I don't think this idea is useful for everyone who plays indoors, even those in similar buildings to mine, but I think there is a niche where it fits. It could be that the benefits of using a spinning barrel are marginal compared to the time and effort of production, but the only way to know is to try. If the idea is a success or a huge failure I wanted to give those interested in this sort of thing the opportunity to find out sooner rather than later.

Do it then, and post the results, enough of the theory, put it into practice.

[Draconis]

Do it then, and post the results, enough of the theory, put it into practice.

The idea is stillborn at the theory stage anyway.

The chances of a foam dart being dynamically stable about its roll axis are zero, because it's a non-homogeneous and flexible material. And for a dozen other reasons. We're talking such long odds that it's easier to win the PowerBall Lotto twice on consecutive draws, than to make such a dart from any form of foam material.

We should make them out of lead! Hmm... But that would require more power. Oh! We could use an explosive, like black powder. Hey... Wait...

[roboman]

If you really cared about spin stabilization, you could just add a tail at the end of the dart (sort of like a Nerf football). I have made little "fletchette" dart, using a toothpick with fins and a noseweight housed in a break-away FBR jacket. However, the fletchettes can embed themselves in corrugated cardboard when shot from a lightly modded NF, and are pretty dangerous for wars, due to their sharp tips.

[nerfnut23]

If you really cared about spin stabilization, you could just add a tail at the end of the dart (sort of like a Nerf football). I have made little "fletchette" dart, using a toothpick with fins and a noseweight housed in a break-away FBR jacket. However, the fletchettes can embed themselves in corrugated cardboard when shot from a lightly modded NF, and are pretty dangerous for wars, due to their sharp tips.

Translation: Sabot round. The reason for the penetration is that there is less resistance from air and less drag=more shooting goodness. And the point is, if you decrease area, but not adjust weight, so penetration increases. So out of a Titan those would be an effective hunting round.

That's because the air escaping behind the dart as it leaves the tip of the barrel is creating turbulence that destabilizes the dart momentarily. If the problem affects your accuracy you may have to drill a few ports just behind the tip of the barrel. This will allow the bulk of the excess pressure to vent away from dart.

You mean a muzzle brake, Slug. And that would get annoying because it means the dart can catch on a port hole and shred, it has happened to me. And it would increase noise, not good things in a war.

[Gyrvalcon]

You mean a muzzle brake, Slug. And that would get annoying because it means the dart can catch on a port hole and shred, it has happened to me. And it would increase noise, not good things in a war.

If you countersink the hole from inside the barrel (dremel +spherical abrasive bit is good for this) you shouldn't have much problem with darts catching. As for sound, I'm dubious that porting would make a significant difference in a nerf blaster, not to mention that noise isn't really an issue with nerf anyways.

[nerfnut23]

You mean a muzzle brake, Slug. And that would get annoying because it means the dart can catch on a port hole and shred, it has happened to me. And it would increase noise, not good things in a war.

If you countersink the hole from inside the barrel (dremel +spherical abrasive bit is good for this) you shouldn't have much problem with darts catching. As for sound, I'm dubious that porting would make a significant difference in a nerf blaster, not to mention that noise isn't really an issue with nerf anyways.

Even then, my stefans shred with the countersink due to expansion And I shoot Log Home foam, or 3M, which is more readily available for me. And if you ever heard my Mega Missile, you would understand. And weird thing is, it outshoots my Titan with 40 pumps with 20. But then again, the dump valve is 3/8" around, and has a tank the size of an AT2K.

EDIT: On topic: Rifling would only count if we were shooting weighted hotglue without foam. But the foam negates the need for it. Rifling is pointless in Nerf guns, THIS WHOLE TOPIC IS FUCKING POINTLESS!!!!!! Sorry, I kinda lost it there.

Edited by nerfnut23, 12 December 2008 - 12:21 AM.