SpudFiles

POLAND_SPUD wrote:well, I think that apart from those living in the US most members live in countries where most of their guns are illegal... so do as JSR says, try to do it on your property, be responsible with it, try not to annoy any one with it (noise!!) and don't tell anyone about it...

Build a containment vessel out of clear plastic (aluminum / steel plates / large tube with caps) and put your targets in there, making sure to seal it well. Done properly, you could fire anything up to a full-sized hybrid in the comfort of your own home (...)

building some sort of a silencer seems like a better and simpler idea

Yeh, except when you start building hi powered rifles your looking at something the size of a large rubbish bin to bring it down to a respectful level.

I shoot at a large bit of steel around 4" thick, completely solid. I put what I want to destroy in front of it and shoot.

Nothing's gone through the steel yet

I agree that drugs and these spudguns are different cases. I've heard that there are other singaporean spudders here, no? limbeh is even incorporating these pneumatics into SCHOOL club activities, but i didnt think it was really legal. Silencers would be incorporated into my other spuds, cause the current one doesnt have extra length for one.

Cheers,
Froze.

btw inonickname, when your projectile actually HITS something like maybe your sheet of steel, does it ring loudly?

Yeh, except when you start building hi powered rifles your looking at something the size of a large rubbish bin to bring it down to a respectful level

yes and no.. if you try to maximise power by using the larges possible chmber then this is true.. but who told that you have to use that 30% more air to get 5% performance increase??

Use GGDT to see how much you can cut chamber volume without significant perfomance drop... apart form making it easier to silence the gun you don't have to use as much air (which translates to -> less pumping/energy used)

POLAND_SPUD wrote:Use GGDT to see how much you can cut chamber volume without significant perfomance drop... apart form making it easier to silence the gun you don't have to use as much air (which translates to -> less pumping/energy used)

Amen, and one should always make sure that dead space, pilot volume etc. are under control to ensure that one is extracting the maximum practical performance for a given quanitity of air, and that other factors affecting power such as the barrel being as long as is practical are maximised.

btw inonickname, when your projectile actually HITS something like maybe your sheet of steel, does it ring loudly?

No matter how silent the launcher, projectile impact is always going to be an issue and there's nothing you can do about it (except shoot only at pillows, but that's no fun :p). However, it's the muzzle blast that sounds more like an explosion and is therefore more likely to attract attention, and this can be dealt with.

I see, but im not really familiar with the terms in GGDT, will figure how to use it sometime. I also dont understand what do i put for each value, like how to measure it.
Alright so projectile impact is non-controllable

Thanks!
froze.

frozebyte wrote:I also dont understand what do I put for each value, like how to measure it.

You can use generic numbers for your valve, say put an opening time of 5-10ms and and a fixed number for flow coefficient, say 5 for a BB calibre launcher and 30 for a 3/4" launcher etc.

If you keep those numbers fixed, you can then play with barrel length, chamber volume and pressure and other facts to see how they will affect performance. The result will not necessarily be an accurate prediction of performance, but for example you will see that making your barrel twice as long gives a significant performance increase, while doubling the chamber volume on the other hand might give you only a tiny performance increase.

I strongly suggest you get to know the program a bit better, you'll be surprised at how much trial and error it saves.

My next project will make a fair bit of noise..I cut up the tubes today for it and rifled the barrel.

1.2m 15.5mm i.d. rifled barrel, 80 cm long chamber, with adapter to use aq hydrogen inlet on the pump I'm making, 400psi, ported by 1/2" qev..

There wont be no silencing that mo'fo

I see, will put some time into it when free time comes.
Abit of OT, but rifled barrels spin the projectile to make it go further right?
And aluminium barrels are strong enough for a 200psi shot?

Cheers.

I tested it to 600 psi and wasn't game to go much further.

Riflings induce a spin on the projectile, reducing tumbling and increasing accuracy, so yes they will increase range.

frozebyte wrote:A bit of OT, but rifled barrels spin the projectile to make it go further right?

It depends on the projectile.

A round projectile won't go further if it's rifled, actually if fired with the same power it will lose speed due to more friction from the rifling and travel less.

A cylindrical projectile without drag stabilising features (forward CG, fins etc.) will begin to tumble the instant it leaves the barrel, without rifling both range and accuracy will be hopeless.

Oh so if i fire round objects rifling is unnecessary, but instead harms the range. But if im using a cylindrical projectile it will need rifling otherwise its going to be hopeless at range and accuracy.

Did i get that right?

frozebyte wrote:Oh so if i fire round objects rifling is unnecessary, but instead harms the range. But if im using a cylindrical projectile it will need rifling otherwise its going to be hopeless at range and accuracy.

In a nutshell. However don't forget that rifling is not essential for non-spherical projectiles, modern tank guns are smoothbores and get fantastic range and accuracy figures without the need for rifling

[youtube][/youtube]

hehe

thanks for the replies!

realised we went far off topic.

jackssmirkingrevenge wrote:

frozebyte wrote:A bit of OT, but rifled barrels spin the projectile to make it go further right?

It depends on the projectile.

A round projectile won't go further if it's rifled, actually if fired with the same power it will lose speed due to more friction from the rifling and travel less.

A cylindrical projectile without drag stabilising features (forward CG, fins etc.) will begin to tumble the instant it leaves the barrel, without rifling both range and accuracy will be hopeless.

I fully agree that it depends on the projectile. In testing barrels for the t shirt competition, a short fat projectile did better. A longer skinny projectile immediately tumbled sideways and flew straight remaining sideways spinning like a propeller. It's range was much worse than a launch from an unrifled barrel where the projectile tumbled end over end.

Rifling alone is not the cure all to projectile tumbling problems. The Arlington team, in launching shirts at the PGE park got an improvement on range on shirts by adding a tail. They wobbled slightly, but didn't tumble.

In regards to smaller chamber, loss of range, low noise, high efficiency, etc. our 700 cu in launcher with the 7 foot barrel has a range of almost 400 feet. With the shorter barrel screwed on the miniature model of the launcher with a 54 cu in tank and 1 inch valve instead of a 2 inch valve, we have a solid range of 200 feet.

Using an overly long barrel on the small launcher provides almost silent shots at high pressure.