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projectile testing - any volunteers?

A place to ask general spud cannon related questions.
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Unread postAuthor: Petitlu » Sat Oct 15, 2011 2:34 am

It is well to want projectiles very stable and very precise but it is necessary to have also an enough powerful weapon to be able to draw far.
The first drank it is that the projectile does not arrive on the target of profile.
Personally I am content with my ammunition with skirt aluminum, not expensive, easy to make, always go right and perforating.

EDIT : I also made a system of shoe which functioned well:

Image

[youtube]http://www.youtube.com/watch?v=UDia6QhbdwQ[/youtube]
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Unread postAuthor: jackssmirkingrevenge » Sat Oct 15, 2011 4:36 am

POLAND_SPUD wrote:If they are close to G8 shape that's already a huge step forward... ohh and don't forget this projectile can have very high sectional density

Personally I like the one that consists of just the cone and the tube - damn simple


I don't think we need another miniboy that's too valuable to lose - ammo has to be cheap


I concur on several of these points.

Going by this list, I doubt we would achieve a Image much better than 0.3 for a capped weighted tube.

Image

On the other hand, if saboted with a simple spindle it can be built with very low frontal area and high sectional density which will convey a tremendous advantage over a conventional projectile.

Attached some GGDT simulations using a 20 gram projectile in a 1 inch barrel fired at high subsonic velocity. In one series I varied the drag coefficient, in the other the projectile diameter (1 inch -> 0.5 inch -> 0.25 inch -> 0.125 inch), in all cases the velocity and weight was kept constant.

I might try a compromise using a delrin endcap with fins milled into it...

Also some more detail of the brass projectile.
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Reducing drag coefficient
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Reducing projectile diameter
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Unread postAuthor: al-xg » Sat Oct 15, 2011 5:24 am

see my point? 


Not if this is still about trying to set a range record.

And I've been under the impression this is what the thread is about, with the whole using a massive hybrid canon and long strips of hopefully deserted sand.

As you said two, different things.

As far as designing cheap repeatable relatively long range projectiles (150-300+m target shooting in my case) there are also things to beat *link to come, too much hassle from my phone, switching to laptop...*

Edit: http://www.bigboreairguns.com/longrangeshooting/500yardtargets.htm

So far I've been using cast lead projectiles with a home-made rifled barrel
It is pretty easy to make projectiles like this: (oh I should point out they had a pointy tip to start off with and were fired at wooden planks then a load of polystyrene and packed tar bags)
Image
But I have already found them to be too inefficient to squeeze the range out of my airgun with the pressures available to me.
The G8 shaped tube tail projectiles may prove to be more a more practical way of increasing the range (if they are re-usable enough, and that has probably more to do with the target material than the projectile), but I am exploring a different route, repeatable cast plastic tail fins for steel/tungsten darts ( I should not have mentioned tungsten :D).
Of course when not trying to shoot 300+m the cast bullets become more practical and cost effective, and when just messing around 14mm spherical lead fishing weights are much less hassle to use.


It is well to want projectiles very stable and very precise but it is necessary to have also an enough powerful weapon to be able to draw far.

It is one thing to want a very stable and vary accurate projectile but it is also necessary to have a powerful enough weapon to be able to shoot far. Critique constructive de la traduction ;)

30m isn't exactly shooting far :P One doesn't need anywhere near the pressure you are using to shoot past 200m especially with an efficient projectile.[/img]

On the other hand, if saboted with a simple spindle it can be built with very low frontal area and high sectional density which will convey a tremendous advantage over a conventional projectile.

Very good point.
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Last edited by al-xg on Sat Oct 15, 2011 12:14 pm, edited 4 times in total.
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Unread postAuthor: The Hellforger » Sat Oct 15, 2011 5:33 am

jackssmirkingrevenge wrote:Going by this list, I doubt we would achieve a much better than 0.3 for a capped weighted tube.


yeah your highest Cd is gonna come from a highly aerodynamic round that is long and heavy

but in this instance we should be talking ballistic coefficient (BC) and not drag coefficient (Cd).

http://en.wikipedia.org/wiki/Ballistic_coefficient

there is alot of stuff in there about it.

using the G8 model for ammunition design is ok but for more efficient ammo you need to bust out the boattail designs from the G7 or even potentially the G5 model.
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Unread postAuthor: jackssmirkingrevenge » Sat Oct 15, 2011 5:49 am

al-xg wrote:Not if this is still about trying to set a range record.

And I've been under the impression this is what the thread is about, with the whole using a massive hybrid canon and long strips of hopefully deserted sand.


Whether they are exquisitely made miniboys or cheap weighted tubes, for range studies there projectiles will definitely need a reliable recovery system in order to give meaningful results, but the point is that it's better to fire off ten cheap projectiles and recover five than fire one superbly build example and lose it.

in this instance we should be talking ballistic coefficient (BC) and not drag coefficient (Cd).


Hence the modelling with reduced projectile diameter, which increases sectional density and therefore ballistic coefficient ;)

Because my head is throbbing and because I can, herewith the APFSDS projectile with fullbore fins I keep banging on about, in 6mm scale using a 2.5mm wall nail. That airsoft BB will made good cheap light wadding :D
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Unread postAuthor: al-xg » Sat Oct 15, 2011 5:53 am

but in this instance we should be talking ballistic coefficient (BC) and not drag coefficient (Cd).


The BC is just a less scientific scientific (not double typing mistake :))way of dealing with empirical data firearm enthusiasts and manufacturers recorded and a way of legacy comparing firearm ammunition.

The BC is not needed at all if you know the projectiles Cd, the drag equation takes both the Cd and projectile weight into account.


Edit: D'oh this is moving too fast.

Whether they are exquisitely made miniboys[...]

That's not really the point that comment was tackling ;) but, yes, there is not point in this if we go out shooting stuff with no idea how far it actually went.

Haha, excelent projectile ! the scary thing is that could be used in an airsoft gun :shock: :)
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Unread postAuthor: MrCrowley » Sat Oct 15, 2011 5:55 am

jackssmirkingrevenge wrote:Whether they are exquisitely made miniboys or cheap weighted tubes, for range studies there projectiles will definitely need a reliable recovery system in order to give meaningful results, but the point is that it's better to fire off ten cheap projectiles and recover five than fire one superbly build example and lose it.

I think you would be lucky to recover one, especially in bores 1" or under (on the assumption a recovery system is not in place).

I think your idea of a tungsten arrow is still worth trying out. They would probably cost $30 per shot but they are easy to make and would go ridiculously far if balanced well.

I wonder how far the small arrow bolts could go with a bit of tungsten in 'em, I have 12 or so in the garage.
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Unread postAuthor: The Hellforger » Sat Oct 15, 2011 6:03 am

al-xg wrote:The BC is not needed at all if you know the projectiles Cd, the drag equation takes both the Cd and projectile weight into account.


but the BC will give you better results for this kind of work alot faster than Cd will.

Cd is used across the board for everything from planes and cars to golfballs and paintballs, while BC focuses entirely on the name of the game here at spudfiles. which is range, power, accuracy
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Unread postAuthor: jackssmirkingrevenge » Sat Oct 15, 2011 8:23 am

MrCrowley wrote:I think you would be lucky to recover one, especially in bores 1" or under (on the assumption a recovery system is not in place).

I think your idea of a tungsten arrow is still worth trying out. They would probably cost $30 per shot but they are easy to make and would go ridiculously far if balanced well.

I wonder how far the small arrow bolts could go with a bit of tungsten in 'em, I have 12 or so in the garage.


Without a recovery system, forget ever finding any of them.

Doesn't have to be tungsten, lead will still yield impressive performance and is much much cheaper.

Haha, excelent projectile ! the scary thing is that could be used in an airsoft gun


I had to trim the tail down because I went overboard with the milling but it made no effect on performance, flew superbly at 10 metres fired at 1/2" plywood. Compare the performance with a lead pellet from the same launcher at the same pressure fired at point blank range, the performance benefits of using saboted projectiles are plain to see.
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Unread postAuthor: POLAND_SPUD » Sat Oct 15, 2011 12:06 pm

what about the one you machined ?
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Unread postAuthor: jackssmirkingrevenge » Sat Oct 15, 2011 12:18 pm

POLAND_SPUD wrote:what about the one you machined ?


Hit the ply nose first at 10 metres, bounced off.

In the meantime, scaled up the fullbore fin design for a 3/4" barrel, herewith some high speed footage (210 and 420 frames per second) of low velocity testing, fired using lung power at cardboard sheet:

[youtube]http://www.youtube.com/watch?v=XVuOWGMYJ1U[/youtube]

Here it is with the wadding disk alongside its little brother, standing on the 1/4" steel plate I intend to fire it at from my 3/4" hybrid. Excrement just got real :D
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Unread postAuthor: dewey-1 » Sat Oct 15, 2011 12:58 pm

JSR;
You are a wind bag aren't you? :D

Very impressive at that size. Send me the dimensions on a picture for CAD model.

Lighten up the wadding puck on the fin side by cutting out a recess.
Cut a notch in rear fins to allow for the recessed area. Could be an angle cut rather than a notch to look better.

Chamfer/radius the leading and trailing edges of the fins will help.

You know my usual questions!
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Unread postAuthor: jackssmirkingrevenge » Sat Oct 15, 2011 1:22 pm

dewey-1 wrote:You are a wind bag aren't you? :D


Every forum needs one :D

Very impressive at that size. Send me the dimensions on a picture for CAD model.

Lighten up the wadding puck on the fin side by cutting out a recess.
Cut a notch in rear fins to allow for the recessed area. Could be an angle cut rather than a notch to look better.

Chamfer/radius the leading and trailing edges of the fins will help.

You know my usual questions!


Any discussion on the matter is moot as I've already turned it into a shower of sparks :D could only find the severely deformed nail, heaven knows where the delrin parts are. I really should stop doing this stuff indoors! I'm starting to think this particular plate is especially hardened, it's tough stuff and I don't remember where I had picked it up from. Test was at 20x by the way :D

For what it's worth, CG was at the start of the delrin section and combined weight of projectile and wad was 9.05g.
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Unread postAuthor: dewey-1 » Sat Oct 15, 2011 1:30 pm

Use Ramset Nails!!!!!

For steel and concrete.
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Unread postAuthor: Hotwired » Sat Oct 15, 2011 1:34 pm

Reminds me of that coin test we did.

The first one I tried was a nail vs a 2p coin.

Ended up looking like that with a small gouge in the coin.

2p coins are actually steel, the coins everyone else had been putting nails through were made of vastly softer metal :roll:



Use an aluminium sheet, should go through it like a nail through aluminium.
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