It was a a few years ago and I threw the paper work away, quite far away probably, so don't remember to decimal points but I converted to seconds and it was between three and four, nearer four, which gave a sense of perspective.  Yes crack to impact would give the average speed.   I think that the crack is good enough to mark the start of the flight.  Though suppose that depends on what the crack actually is, I've made some slings which don't ...ever, so, sadly, it's not the glans briefly exceeding the speed of sound,  not this slingers casts anyway.  It's probably either a whip like effect with the release cord or a air rushing in to fill a partial vacuum.  That's a problem for another day, for this the main thing it that it happens at the beginning and that is good enough to mark the start of a sound sample which, if we can work out long range sensing, would be several seconds long.   What I'm after is something that would give time and position from any  point in flight to any other point in flight.  The velocity falls off quite sharply I think.  Interesting links, triangles.  I suppose if applied to glans manufacture it could be done with folded cardboard, I'll bear it in mind thanks.  I must admit that I'm stuck on the analytical maths and physics of this one.  Wish I could ask a bat, it'd know, probably laugh at me; compared to echo location it's nothing..  Maybe we could just sling bats and not let them have another go until they told us how fast they'd been going.   In the hope that my mind freshens up after a gap, often does, or someone else works it out or , and this would be totally cool, someone doing a degree decides to take it up as an honors project and maybe produces a program which automates the lot outputting a ballistics graph after recordings,  microphone and slinger positions are input, I'll concentrate on producing a loud glans for now.  Get some plasticine and do a little finger thinking.

I don't know maybe they think that I really do have a gold glans and on further reading discover it to be imaginary and abandon the thread in disgust.  Just as well probably, wouldn't want some hopeful person hassleing me for something which would probably be worth more than all my worldly goods. 

I've also realised that I've casually mentioned a brand product on a global website without having any idea how widely it's distributed ( sorry didn't think ).  Plastecine is a modeling clay, I think that it is a fine clay mixed with an oil, by the smell I guess linseed is involved.  It doesn't set but is  soft warm and  firm cold, in this weather it'll be close to hard outside.  I like the stuff,  as a child I played with it a lot as it could be anything, I've also used it to form paper mache puppet heads etc on.  I hope it will be ideal for testing gland shapes as it is reasonably heavy and though it will go out of shape on impact will leave the sling and fly in whatever shape I mould it. .   Actully it is the sort of thing people who can sling in big indoor places, like Tint in his video,  might enjoy if they don't mind reforming it for each shot.  No danger of rebounds, any shape you feel like trying, could even do target practice at a bed of nails. Probably around the same mass as a clay glans and that was good enough for many an ancient army,  way better than tennis balls.

Or perhaps my posts are just too long and rambling.

Umm. Plasticine - loved the stuff - now seems to have become a specialist product. Use it in disappointingly small quantities in my (ahem.) day job. Good info on Wikipedia.

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

I agree with you for the models. I suppose a refrigerated plasticine glans would be pretty effective though ?

I've wondered about using polymer clay for making prototype glandes. Has anyone ever tried the stuff? I havn't any experience of it myself .

Stringman: This velocity determination stuff... since I think I might be able to help you I sent you an 'Instant Message'. Don't know if you've read it.

While you were posting Wander I was messaging you.  I loved wallace and gromet, really funny.  Even managed to be  serious at the same time and stayed funny, chicken run had a dark side to it too.  If we had lots of money and the sort of studio that Parks has got we'd solve the velocity problem easily.  On the other hand if we can sus it with sound   most people could do it, well the lucky few on this planet anyway, those with the luxury of pc's and internet t probably have sound recorders knocking about.    

Cold plastecine is seriously hard, maybe in hot areas you'd want an insulated bag and one of those blocks of gell which stay cold.  Not nessesary in Derbyshire at the moment.   I've used something called tabular aluminide which is like a concrete sort of thing, feels more like apoxy resin to make up, uses hardly any water.  When it sets it is hard enough to survive big impacts and has around the same mass as granite.  But it is expensive so I won't use that untill I have the design of the loud glans right.

the speed testing thing?  i don't know if the loops are magnetically charged and detect when the metal passes through the loops.
or maybe the loops make up sort two walls of magnetic that will detect when they are broken.

i know that both of them sound the same, but the one on top will depend on a metal projectile, and the one on the bottom will not matter what the projectile is made from.

or maybe they just detect the air disturbance or the sound break
or maybe they detect the air disturbance

i don't know.  i will look for some reading on that

They are optical.

The diffusers are just strips of translucent plastic that give the photocell "eye" a nice even white backdrop. As the projectile goes through, the sensor sees a tiny dip in the light level and triggers a timer, that is stopped by the second sensor.

It would work fine for slinging provided you could hit the target area. Setting up behind a (think) sheet of plywood with a hole cutout would probably save you a considerable amount of money in replacement chronys.

I think the only reason that 10ft is recommended is to avoid any potential muzzle blast - I know archers and airgunners shoot from up close. The further away you are the more the projectile is going to have slowed down. This might seem silly, but if you are trying to measure muzzle velocity, a few extra feet can make a big difference.

Matthias

Ok.....since you said "you'll be kings".....


Looks like Goliath's gettin a beating tomorrow....


TS