SpudFiles

a little tip, those sabots can eject from the projectile easier if you machine a groove on the front of the sabot. like a spoon to shovel up air resistance.

MrCrowley wrote:Oh and if the dart ends up tumbling you could try and grind down the fin edges on a slant to induce a spin, I think Ragnarok brought the idea up once in a bottle rocket thread and i've been keen to find how well it works. It could help with penetration and drag too.

It was my thread on darts, but that's not important right now.

It should help noticeably with drag for two reasons - it reduces the axial portion of the drag force by shifting the drag vector away from the axis of travel. The other thing is that once spinning, the fin's leading edge has a reduced velocity of incidence with any air particles, further reducing the drag force from the fins. (My own design should be able to travel a quarter mile losing only 40 of it's initial 900 fps - less than 10% of the muzzle energy lost. That's leagues beyond what any real firearm could do.)

The penetration is a slightly different matter. Obviously less drag means more energy carried into the target, but a fin is still a potential problem in that area - that's why my design has fins that are designed to break free on impact with minimal energy, while still managing to give most of the energy they carried into the penetration.

starman wrote:Stability and thus accuracy in flight is the purpose of the twist, not just sheer velocity. If the shot is a 1 meter blast into plate steel it's no big deal. If it's a 100 meter or further shot into anything it could be a big deal.

Actually, the idea of dart spin as I presented it has nothing to do with stability. Darts are far too long to stabilise with a spin, that's why APFSDS rounds from tanks tend to be fired from smoothbore barrels.

Normal rifling does two things - stabilise and equalise drag. The fins themselves should provide enough stability (actually, I have another fin design that should improve stability, but at the expense of a slight increase in drag), so trying spin to improve that is moot.
The equalisation of drag is the important bit here - by spinning the dart, any slight difference in drag on one side that would normally curve the projectile out of line is balanced out, so the projectile actually travels in a tiny corkscrew.

Angled fin leading edges is a fairly serious proposition as I see it.
With well made darts and a consistent launcher, you could be looking at impressive groupings out at past hundreds of metres.

*drool*
Nicely done Larda!
My girlfriend asked why I never looked at her the same way I just looked at the screen.

I would like to ask, why is there a "fat" part on those darts?
It will require to make a larger diameter hole doing so, and thus you could make the rest of the body behind that also that diameter (extra weight).
Or is it for the fins? I guess you should make them break and fall off on impact for best performance.

i would try nothching a round bullet, so fins slip in, letting them slide free on impact. Like this:

_ _
female: |_ _ _|
Male: _| |_
|____|

ma;e would be fin.

psycix wrote:
I would like to ask, why is there a "fat" part on those darts?
It will require to make a larger diameter hole doing so, and thus you could make the rest of the body behind that also that diameter (extra weight)

I think it's to move the centre of gravity forward.

psycix wrote:My girlfriend asked why I never looked at her the same way I just looked at the screen.

I got exactly the same indignant question while visiting a friend (:D) in Moscow the day she took me to the military museum hehe

wow amazing creation! You seriously needed those air dampers:) Nice other videos/projects as well!

You know your gun shoots faster than a 50. cal sniper?

Very well done. and is that 933.3 miles per second?

Metres per second.

It's about 2090 miles an hour.

Holy sh!t man!!!

That's the most craziest homemade gun i've ever seen in my whole life. I've just did a conversion from 933.3m/s to 3062.88FPS. It is faster than an .50cal BMG round. If there was a war going on you could probably start you're own militia and be the leader of it.

Two simple words.

Holy shieettttt.....

Bravo Larda! it's the only thing i wanna say...

What kind of pressures are in the chamber pre-ignition?
How do you stop the propane from liquidizing at 177psi?
How can you put 200x into a chamber and not get 177psi?

I'm clueless, sorry.

Where to go for an introduction to hybrids?
Has someone written a guide?

I want to make a high compression propane/oxy hybrid.

When does propane become liquid?
How exactly are you igniting this? I see the little spark gap... why doesn't this get blown away?
What metal are those wires made from?

fogus wrote: I'm clueless, sorry.

Then a hybrid, especially one like this is no where for you to begin. Have you built a standard combustion or pneumatic spudder before?

If you are indeed new to the hobby, take a good long look at the burntlatke site. That will get you well on your way.

fogus wrote:How do you stop the propane from liquidizing at 177psi?

The important factor is the partial pressure, not the total pressure. Partial pressure is total pressure times percentage of gas mix.
This means the partial pressure on the propane is only about a 25th of the total pressure in the chamber.

Hope that helps.