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Marble inaccuracy

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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how to make it more accurate.........

Rifle it
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use new ammo (darts)
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get used to it
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Total votes : 8
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Unread postAuthor: skinner » Fri Jul 13, 2007 1:26 am

They dont fly straight because of the magnus effect.
Im not exactly sure what the hell the magnus effect is.
But I know its got something to do with it.

Making the marble spin on an axis will help significantly.
Applying backspin will increase distance.
As for accuracy, Im assuming, that the marble will rise in the air, so, you would have to counter for that.

Hope that all helps, sort of.

--Skinner
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Unread postAuthor: chaos » Fri Jul 13, 2007 2:19 am

ive only realy had the problem with cat eye marbles they seem unbalanced with the funky shape in the middle. but then again my target (serious ammo) is lead balls so i dont usually have to deal with this problem
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Unread postAuthor: Modderxtrordanare » Fri Jul 13, 2007 2:29 am

skinner wrote:They dont fly straight because of the magnus effect.
Im not exactly sure what the hell the magnus effect is.
But I know its got something to do with it.

Making the marble spin on an axis will help significantly.
Applying backspin will increase distance.
As for accuracy, Im assuming, that the marble will rise in the air, so, you would have to counter for that.

Hope that all helps, sort of.

--Skinner


The Magnus Effect is a variation of Bernoulli's Principle. When you shoot the marble, (with a hop up of sorts) the rotation of the marble as it flys through the air causes the air on one side of it to flow with the movement of the projectile. However, the other side is going against the movement of air causing a decrease in velocity on that side, and an increase in velocity on the side that is rotating with the airflow. The difference in velocity causes the marble to "swerve" or fly off course from it's expected direction, and unless you somehow manage to keep it from spinning during flight, it is going to experience the Magnus Effect.

Though, if you'd like to see Bernoulli's Principle in action, go grab a piece of paper and hold it by two corners, along the shorter side. Put that short side up near your mouth in between your lips and blow across the top of the paper. By doing such, the air is moving faster on the top part of the paper as compared to the bottom, thus pulling the paper upwards. It's kind of something one does in school, but it still gives you the idea of what's going on if you haven't been taught.
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Unread postAuthor: MrCrowley » Fri Jul 13, 2007 3:58 am

chaos wrote:ive only realy had the problem with cat eye marbles they seem unbalanced with the funky shape in the middle. but then again my target (serious ammo) is lead balls so i dont usually have to deal with this problem


I think someone needs to make a cricket ball gun don't ya think? It would be expensive with the most budget balls being like $15 but it would be fun as hell. You could even shine the ball up on one side and see if you can get it to swing, thought technically it wouldn't unless the seam is straight.
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Unread postAuthor: sniperjosh » Fri Jul 13, 2007 4:29 am

How inaccurate are we talking?? I use marbles alot with smoothbore, accuracy is fairly solid, not really anything that compares to a sphere for smoothbore barrels. simple way to increase ACCURACY would be to use heavier marbles, or metal ball bearings. Of course this will result in a loss of fps, but they will be more accurate.
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Unread postAuthor: VH_man » Fri Jul 13, 2007 5:36 am

well, i did two things.

1. i looked down the barrel with a flashlight........

lets just say its scratched up, and dented, and everything like that. im gonna go get myself a new peice of copper tonight.

2. it actually does fly fairly straight. the extrememe curve i saw was actually the marble hitting a tree and reflecting off of it, and me not hearing the noise if it hitting the tree over the echoing muzzle blast.

basically, im going to go get myself some new copper, a pipe cutter, and some steel balls. hopefully, i can get this thing accurate. when it is, ill post it here with what i did. im still going to go with a hop-up system, btw.......
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Unread postAuthor: lukemc » Fri Jul 13, 2007 6:13 am

i would do something like this it you want spot on dead accurate marbles. CLICK ON THE BLUE TEXT
the long tail prevents any spinning at all so it would be consistant
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Unread postAuthor: psycix » Fri Jul 13, 2007 6:28 am

Use 2 marbles in front of each other and tape them together. The tape will seal the barrel better and the projectile will not be round anymore but more a cillinder with round ends.
Maybe that will fly better?
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Unread postAuthor: al-xg » Fri Jul 13, 2007 6:37 am

The two marble idea wouldn't work without the rifled barrel though... it will tumble like most cylinders. If you decide to change the ammo, rifled projectiles or darts work great but then it wouldn't be a marble gun.

Using a pipe cutter deforms the pipe so don't use it on the muzzle end.

Are the marbles a tight fit in the copper pipe ?
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Unread postAuthor: spud yeti » Fri Jul 13, 2007 6:44 am

Using a pipe cutter deforms the pipe so don't use it on the muzzle end.

Not if you use it properly it wont. If you twist it around many times without too much pressure and slowly tighten it, it shouldent deform the pipe. Then you get a flat metal file and smooth the edge to eliminate the slight closure of the pipe.
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really good quote/phrase here
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Unread postAuthor: lukemc » Fri Jul 13, 2007 7:01 am

if you decide on darts there are some very nice how-to for small bore darts ill post the 2 ive made and know they work

A-98's darts

NOnames darts
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Last edited by lukemc on Fri Jul 13, 2007 8:00 am, edited 1 time in total.
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Unread postAuthor: Insomniac » Fri Jul 13, 2007 7:37 am

The link for A-98's darts isn't working. The error message is kinda funny though.
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Unread postAuthor: VH_man » Fri Jul 13, 2007 4:54 pm

well, i cut off the hop-up part.

i found out my problem........ If i look at the muzzle end of the old barrel, i did not do a very clean cut....... at all............

this time i cut it with a hacksaw, then beveled the edges inward....

its pretty accurate now. i can hit a peice of wood 4 inches across by 10 inches high from 100 feet every time.........
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Unread postAuthor: f.c » Fri Jul 13, 2007 6:21 pm

i never get too bad accuracy. but usually i sabot my projectiles with tissue papers. try that maybe ?
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Unread postAuthor: Modderxtrordanare » Fri Jul 13, 2007 6:23 pm

f.c wrote:i never get too bad accuracy. but usually i sabot my projectiles with tissue papers. try that maybe ?


VH_man wrote:its pretty accurate now. i can hit a peice of wood 4 inches across by 10 inches high from 100 feet every time.........


Try reading the entire thread f.c.
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