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"Sniper" Guns

A place to ask general spud cannon related questions.
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"Sniper" Guns

Unread postAuthor: skyjive » Tue Jun 03, 2008 7:25 pm

So I've seen a lot of cool-looking so-called "sniper" designs lately that inspired me to do some thinking about the degree of accuracy that is attainable with spud guns. Most of the designs I've seen have no particular feature that would justify the name "sniper" apart from the aesthetics of the weapon. Of course a real sniper rifle gets its accuracy from firing rotated projectiles at extremely high velocity from a very precisely manufactured system.

My question is, to what extent have people been able to get any degree of accuracy at long ranges with spud guns? My personal best is hitting a fairly thin tree at about 75m (admittedly a lucky shot). I was firing prone off a bipod and using a cheap rifle scope, shooting about 5 degrees above the horizontal. I was shooting batteries wrapped in a thin layer of duct tape with a tail assembly made out of a drinking straw and three cardboard fins angled so as to rotate the projectile in flight.

For a really accurate spud gun, you would need to rotate your projectiles, either via rifling or fins, and you would need a high velocity, low drag uniform projectile. The idea of using a sabot appeals to me since it allows a wide barrel for good internal ballistics but at the same time a small projectile for good external ballistics. The trouble is that I can't think of a way to make the sabot both light enough (so as not to waste a significant amount of the energy of the shot on accelerating useless mass) and precise enough so that the projectile isn't forced off course before the sabot discards.

Does anyone have any ideas on the subject, or made something already that has the goal of extreme range and accuracy?
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Unread postAuthor: pizlo » Tue Jun 03, 2008 7:31 pm

There has been a LOT of discussion of ammo, fins and such, try to find those topics, look in the theories section.
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Unread postAuthor: VH_man » Tue Jun 03, 2008 7:32 pm

Darts.

I would say search but you have put quite a bit of thought into your post, so i will help you.

To get GREAT accuracy, i reccomend something that resembles a blowgun dart.

Also, if you want to get technical, anything that will remain stable in flight will work. i wont go into the physics of it all but basically, the further twoards the tip of your projectile the Center of Gravity is, the more stable the projectile will be. AKA a dowel with 80% of it hollowed out will make a very accurate projectile, even more so if you slap a screw in the top of it to add more weight.

for less-good accuracy (me english very well today) use spherical projectiles, like Ball Bearings.

for the BEST accuracy, rifle your barrel.
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Unread postAuthor: nivekatoz » Tue Jun 03, 2008 9:02 pm

I would have to say my cannon is by far ( NOT ) a sniper.. I justed named it because other people named there cannons in a simaler fashion...It still packs a punch!!!!............Im working on the sniper thing. Im sorry for misslableing my cannon.....
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Unread postAuthor: skyjive » Tue Jun 03, 2008 9:25 pm

Nivekatoz, my thread was intended to be a discussion of the finer points of constructing an accurate weapon, not an attack on people who name their guns certain ways. Don't worry about it.
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Unread postAuthor: subsonic_karet » Tue Jun 03, 2008 9:59 pm

Don't be fooled by the whole "rifling" myth. While rifling does help in accuracy it is not the only factor. Over the last few centuries ballisticians(sp?) have been trying to perfect an accurate firearm/projectile. It is not just the firearm that is assumed to be accurate but more so, the projectile's consistency. Without a consistent projectile you have know way to measure accuracy. It's not one type of projectile over another, but more like one projectile being compared to itself. If you don't have a consistent projectile, it doesn't matter what rifling twist you have, you won't have a consistent measure of accuracy.
Now you can't compare results from a "dart" to results from a potato. They are not like nor will they ever be like. You have to define accuracy, in the real world MOA(1"/~2.9cm @100 yards/91.44m). Being able to hit a spot consistently and it's deviatian from original spot will result in a level of accuracy. Specific rifling for specific projectiles will render specific accuracy results regardless of the projectiles shape.
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Unread postAuthor: jackssmirkingrevenge » Wed Jun 04, 2008 4:26 am

The closest analogy you can find in the firearm world to spudguns as far as smoothbore barrels are concerned is the 12 gauge shotgun. I would say it is very possible to make a spudgun that could consistently shoot inside a 6" circle at 50 yards, however your ammunition and launcher have to meet a set of criteria.

First of all, your setup must be consistent - always filled to the same pressure, valve opens with the same speed etc. - as should the ammo be of consistent dimensions, shape and weight. Rifling isn't necessary, modern tank guns have smoothbore barrels yet they are capable of killing enemy tanks with a first shot more than 3 kilometres away. In order to ensure that your projectile is stable in flight, look to shotgun slugs for inspiration. The important thing is to keep the centre of gravity forward, either by using a hollow tail or by attaching a lighter section to the base of the projectile as used in the brenneke slug (ignore the "air rifling", it doesn't have an significant effect) - if you do this, you won't need fins.

Secondly, you must have a good sighting system, either iron or optical sights, that is firmly attached to the launcher and can be zeroed to the actual point of impact. Obvious, but worth mentioning.
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Unread postAuthor: Ragnarok » Wed Jun 04, 2008 5:31 am

If there is such a thing as a reasonable claim to a "sniper" launcher, I'm slowly trying to work towards it.

I've been studying internal and external ballistics with the intent of making a my next launcher far more accurate, and I have what would pass for a small thesis on the subject, and it involves subjects such as recoil control, muzzle blast, projectiles, barrel geometry - the works really.
It's far from publishable in it's current state, but along with a myriad other articles I have, they're all being polished up into a more practical book form, which I will likely make available in pdf form when it's all done.

That's not my sole aim for my next launcher though...
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Unread postAuthor: Boom_erang » Thu Jun 05, 2008 2:47 pm

Skyjive,

Good post - this is something I've been pondering as well. Plenty of good info in the thread already. Another factor is the density of the ammo. A less dense object will be more affected by wind resistance and wind shear. This is one reason that .50 sniper rifles have been all the rage lately. They of course also have a very high power and thus flatter trajectory. It looks like the newer .416 round is starting to get some notice as well. Not as much mass as .50 but flatter trajectory and more ft-lbs of force on impact at greater distances.

I agree that some kind of dart with a dense core would be best - with the weight near the front. Your battery design with fins already approaches this. Spin can help also to give the projectile some gyroscopic stability.

I'm looking into these same things with the intention of building a silenced combustion "sniper" gun. So I'll follow further responses with interest.

-B
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Unread postAuthor: hyldgaard » Thu Jun 05, 2008 3:19 pm

To be honest there is a lot of really good ideas for improving accuracy floating around on this forum, the only problem is that almost all of them is almost not achievable in the world of spudding - not practically anyways. Almost anyone on this board can sit down and make a very nice projectile, the main problem is just that it takes a lot of time per piece. my contribution to this discussion would be that you just focus on some of the most important things when it comes to designing the ammo, but also keep in mind that it has to be easy to make rather uniform and not too timeconsuming. I looked into small caliber lead slugs, wich i have had great results with. The things i keep in focus when making my slugs is making them as much alike everytime, and keeping the nose as heavy as possible while keeping the tail as light as possible. Also, when i fire my gun i try to keep it at the same pressure every time. With this combination i would say that im quite pleased with the accuracy, i can reliably hit a 10cm(~4") circle at 25m.
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