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What is a good accurate gun...

A place to ask general spud cannon related questions.
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What is a good accurate gun...

Unread postAuthor: Dussalater » Thu Sep 25, 2008 3:49 pm

I recently made a spud gun and it fires with great speed but it has suck a huge kick that i cant aim woth nuttin with it.. I am look for a strong, accurate gun that fires small projectiles preferably.. Does anyone know a tutorial or can give me some tips on constructing one?
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Unread postAuthor: Gippeto » Thu Sep 25, 2008 4:08 pm

The layout of the barrel and pivot point (butt plate on the stock) will greatly (but not exclusively) determine "how" exactly a given design will react under the forces of recoil.

If the barrel is higher than the pivot point, the forces acting on the projectile WILL cause the muzzle to climb.

A consistent technique should have yielded consistent results. :? Are you perhaps flinching?

However, there does exist a simple solution to muzzle rise. Place the barrel closer to the same plane as the pivot point. (look at an M16 if you don't understand)

The force (recoil) acting on the pivot point will have a smaller moment arm to act on and muzzle rise will diminish.

If you were to go to an extreme, and place the barrel on a lower plane than the pivot point, you would actually experience "muzzle drop".

That would be different. :roll:

Overall, it sounds as though you are looking for a copper gun.

Check out the pneumatic showcase section. There are lots of ideas to choose from.
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Unread postAuthor: iisthemuffin » Thu Sep 25, 2008 4:11 pm

Yes i can give you one HUGE tip that will help you SO very much.


http://www.spudfiles.com/forums/cannons ... html#13305

Take a look.

I do not intend to be rude either. Just take a look around the showcase. Alot of cannons if not all have specifics about the gun telling you exactly what they used. Try looking and maybe you could copy or modify a design of your liking.
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Unread postAuthor: Hotwired » Thu Sep 25, 2008 4:29 pm

One of these days I need to record myself firing my cannon to see if there is any notable recoil. I don't seem to notice any over all that blast.

1/2" or 15mm barrels or smaller should be what you're after if you're firing slug type things and not beads/pellets. If it's pellets then try and find some extruded aluminium or brass tube in Xmm ID in your DIY store.

As for accuracy... all smoothbore spudguns firing unstabilised projectiles have fairly poor accuracy after a few tens of metres. Even though the maximum range could be hundreds of metres.

Try using dart type projectiles, they don't have to be razor sharp skinny devils, a stick of dowel with fins at one end and a weighted nose will fly in a flatter arc than a potato.

For very small bores you can use nails without heads and a short fluffy unravelled string tail for quick and economical darts.
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Unread postAuthor: ALIHISGREAT » Thu Sep 25, 2008 4:46 pm

Gipetto is right, if you have a stock, make sure you mount it so the recoil will come straight back...

and Gippeto was right about the M16, but he could have included the M14 into the explanation :wink: the M14 recoils like a beast because it has a wonky stock that isn't inline with the pivot point (its not just the fact it fires 7.62 rounds) so when they designed the M16 to replace it, they made the stock straight and raised the sights.

and also you would try adding a muzzle brake http://en.wikipedia.org/wiki/Muzzle_brake a tee on the tip of your barrel should work ok.

oh and a bipod

p.s. any pics/link of this cannon?
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Unread postAuthor: jackssmirkingrevenge » Thu Sep 25, 2008 5:18 pm

The most important thing for accuracy is consistency. This means always filling to the same pressure, using a valve that always opens with the same speed and can be operated without shaking the launcher unduly, and ammunition of regular shape, size and weight. In the latter regard, building a launcher chambered for commercially available ammunition such as airgun pellets of airsoft BBs is a good idea.
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Unread postAuthor: Ragnarok » Thu Sep 25, 2008 6:11 pm

Gippeto wrote:However, there does exist a simple solution to muzzle rise. Place the barrel closer to the same plane as the pivot point. (look at an M16 if you don't understand)

The force (recoil) acting on the pivot point will have a smaller moment arm to act on and muzzle rise will diminish.

Actually the pivot point is pretty irrelevant for single shot rifles - it's only any use for controlling the muzzle rise of automatics.
The lock time is so short that the pivot point doesn't have time to come into it. If you study a slow motion video of any gun's recoil, it's fairly clear the person holding it doesn't actually start to affect the recoil (i.e. their hands/body don't start to recoil themselves) to any significant degree until well after the bullet is gone.

This is a fairly good video, although I'd have preferred even slower so the bullet itself was clear. Notice how the pistol has actually moved quite significantly before the guy's hands start to absorb that recoil:
http://www.youtube.com/watch?v=AMdr5HQWUck

Now I know spudguns have longer lock times, more in the realm of air rifles than powder burners, but even then, the pivot points and hold only really become important with springers, which recoil before they fire, which means assuring consistent recoil is the key to their accuracy, and even then, a poor hold won't cause a shot to go completely wild, it should likely hold within a couple of dozen MOA of where it should have.

(@AliH: Muzzle brakes are even less use for single shot accuracy - they can't do a thing until the gases reach them - i.e. when the bullet has gone past and all ready left the muzzle)

The important factors for controlling recoil and accuracy on a single shot are:
- centre of gravity compared to the recoil direction
- overall mass.
- overall rigidity and harmonics
- minimising effects of muzzle blast on the projectile. Air strippers or vented barrels are two ways to cope. Air strippers redirect muzzle blast, vented barrels reduce the muzzle blast.

I suspect that most spudguns are let down by fairly loose/flimsy barrels and poor muzzle blast over anything else (of course, ignoring inconsistencies in the ammunition/fill pressure - we're assuming those are already controlled).

And given the long barrels, barrel harmonics may also come into play (barrel harmonics are related to the square of the length of the barrel, so damping/securing it in various places to cut the apparent length may will be wise.)

For an example of reasonable accuracy, HEAL is fairly weighty, has a rigid barrel that's tied down so it can't flail about (no sense in free floating a single shot pneumatic barrel!) which produces reasonable results - the barrel is also polished, teflon lubed, straight and free of any dents or blemishes.

I was trialling a combination venting/airstripper attachment a while back, which was giving decent results, effectively whittling the muzzle blast away to nothing - I'll be souping it up a bit, and hopefully it'll do the job for "later plans"
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Unread postAuthor: Gippeto » Thu Sep 25, 2008 11:27 pm

Actually the pivot point is pretty irrelevant for single shot rifles - it's only any use for controlling the muzzle rise of automatics.

Ever been whacked in the cheek by a light weight 12ga ? You would change that opinion, and your technique, and quickly. :wink:

I liked this one better. Wait for it, the shot is around 5:16. :roll:

http://www.youtube.com/watch?v=3Cq7rjnv ... re=related
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Unread postAuthor: starman » Fri Sep 26, 2008 12:13 am

The "kick" as you call it is based entirely on the mass and velocity of the projectile...the whole equal and opposite reaction thing. If your recent spud gun had a 2" barrel and you were feeding fairly large potato slugs into it, that was the basis of your "kick".

If as you say, you scale your projectile mass down, your associated kick will also be much less.

Consider a nice copper pneumatic like Rag's HEAL.
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Unread postAuthor: ALIHISGREAT » Fri Sep 26, 2008 1:26 am

i disagree about the muzzle brake, it reduces the effect of the recoil from the gas an helps make the gun quite a bit louder to the shooter :D
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Unread postAuthor: Ragnarok » Fri Sep 26, 2008 6:59 am

Gippeto wrote:Ever been whacked in the cheek by a light weight 12ga ? You would change that opinion, and your technique, and quickly. :wink:

Sorry, bad wording. How's this:
Any effects of muzzle rise (caused by pivot points) on accuracy are minimal, because the lock time is far too short for the pivot points to have any play in the matter.

And no, no accidents with light weight shotguns - I'm fairly lucky to have fired any shotgun at all, what with this country.
Anyway, you're talking to someone who's primary shooting technique revolves around barely holding the rifle at all - that's how springers should be shot.

I liked this one better. Wait for it, the shot is around 5:16. :roll:

Ah, but I know some people don't have super zippy connections, so I picked the short 10 second video.

@Starman: Well, the gases themselves make quite a significant recoil contribution. In HEAL, the gases tend to weigh almost as much as the projectile, and are going a lot faster, so typically the gases are actually the primary source of recoil!

ALIHISGREAT wrote:i disagree about the muzzle brake, it reduces the effect of the recoil from the gas an helps make the gun quite a bit louder to the shooter :D

Ah, but for a single shot pneumatic, it cannot improve the accuracy.
Things like that worked wonders on the Thompson SMG, but it's not going to help here.

Also, louder to the shooter is not a good thing when it involves the potential for damaged hearing.
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