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The whistling sling balls of the Burnswark battleground (Read 11080 times)

JoergS

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The whistling sling balls of the Burnswark battleground
Aug 12^th, 2016 at 5:52am

Hi guys, haven't posted here for a while... but recently I did some work with Dr. John Reid of the Trimontium Trust. These guys did some excavations at the 2nd century (AD) battle ground at Burnswark/Scotland, where a Roman legion laid siege (and eventually stormed) a Caledonian fort.

The Romans bombarded the hilltop fort with thousands upon thousands of missiles. Arrows, ballista ball, and many many sling balls. Launching distance 120 to 180 meters, steeply uphill.

Curiously, about 20% of the balls they found at excavations were smallish (20 grams) and had a precisely drilled hole, 4mm wide and 6mm deep.

There are several theories why the Romans drilled those holes, one of them says that the balls whistle that way and it was psychological warfare...

John came out for some experimental archaeology - it was fun! Maybe this is interesting for you guys too.

https://www.youtube.com/watch?v=7vJBKfQFD8I

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Curious Aardvark

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Re: The whistling sling balls of the Burnswark battleground
Reply #1 - Aug 12^th, 2016 at 7:05am

So the holes didn't go all the way through the balls ?

And next time you need a proper slinger - let me know, have slings - will travel

The sling pouch on your trebuchet, didn't look great for imparting spin. Nees to be a lot flatter so the ball more or less rolls out.

But great experiment and worked really well with the slingshot Thumbs Up

Do All things with Honour and Generosity: Regret Nothing, Envy None, Apologise Seldom and Bow your head to No One - works for me

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JoergS Tiro Offline Weaponizing rubber since 2008. Posts: 33 Gender:	Re: The whistling sling balls of the Burnswark battleground Reply #2 - Aug 12^th, 2016 at 9:57am The holes are drilled in 5 to 6 mm, no more. The pouch for the rubbuchet has to be boat shaped because otherwise it may not catch the ball at the start of the throw. Who knows, in case the video is a success we might all meet in Scotland for a follow up!
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Curious Aardvark

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Re: The whistling sling balls of the Burnswark battleground
Reply #3 - Aug 12^th, 2016 at 12:32pm

could be fun. Not been up north to the barbarian lands for decades.

I'll design and print a mould to make concrete, clay etc whistling balls.

Figure either clay or cement with lead shot mixed in for weight.

Wonder if you still get the noise if you scale everything up and keep the holes proportional.

Or will the same size hole in a larger sphere make the same sound.

There is experimenting to be done

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JoergS

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Re: The whistling sling balls of the Burnswark battleground
Reply #4 - Aug 13^th, 2016 at 5:24am

Actually I saw a documentary on TV where people shot a bowling ball from a cannon, and it DID whistle. The bowling ball has finger holes of course.

Taofledermaus (Jeff) also wants to make a shotgun slug with holes, to see if it whistles...

Also, I have received many comments saying my penetration tests were useless because I shot at point blank. I did use the online trajectory calculators and the result was that the speed of a lead ball lobbed by a sling did not decrease much at all during its flight, maybe 5% or so. Can you confirm?

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Bill Skinner Forum Moderation Offline Slinging Rocks! Posts: 3292	Re: The whistling sling balls of the Burnswark battleground Reply #5 - Aug 14^th, 2016 at 10:00am As far as the lead balls losing velocity, it doesn't matter how it is launched, once it achieves velocity, it will slow the same due to gravity and air resistance.
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JoergS Tiro Offline Weaponizing rubber since 2008. Posts: 33 Gender:	Re: The whistling sling balls of the Burnswark battleground Reply #6 - Aug 14^th, 2016 at 11:16am Gravity does NOT slow down the horizontal speed of a bullet. It simply adds a downwards vector. Air resistance does slow things down, but the air resistance of a lead sling ball is low.
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Curious Aardvark

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Re: The whistling sling balls of the Burnswark battleground
Reply #7 - Aug 14^th, 2016 at 12:19pm

over that short a distance (150-180 metres with lead is short distance for slings), and given that gravity accelerates the downward velocity - it's going to hit pretty damn hard and still be spinning very fast at the point of impact.

So we're going for the size and depth of hole is the relevant part not the size of the ball Which make sense.
Lead bullets were small for the obvious reasons. Density means they still have a serious impact and smaller bullets means you had more of them.

Okay i'll make a decent sized mould for clay balls, say 30mm diameter, with a 4mm x 6mm hole.
And see what happens.

Figure the easiest way is to make a cylindrical insert and cutout on the edge of the mould, so that the hole is made when you press the two halves together.

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Curious Aardvark

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Re: The whistling sling balls of the Burnswark battleground
Reply #8 - Aug 14^th, 2016 at 1:34pm

Script is totally parametric. So I can make any size mould with any size insert. same script will be used to generate the insert cylinder.

I'll do the inserts and then print a couple out for testing purposes

These are all the things you can change:

bd=20; //ball diameter
hl=6; // hole length
hd=4; // hole diameter
mb=4; // mould border width
pl=4; // peg length
pd=4; // peg diameter
pde=4; // peg distance from edge

whistling_bullet_mould.png (15 KB | 152 )

whistling_bullet_mould-insert.png (8 KB | 181 )

Do All things with Honour and Generosity: Regret Nothing, Envy None, Apologise Seldom and Bow your head to No One - works for me

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Curious Aardvark Forum Moderation Offline Taller than the average Dwarf Posts: 13965 Midlands England Gender:	Re: The whistling sling balls of the Burnswark battleground Reply #9 - Aug 14^th, 2016 at 2:08pm Okay should have a20mm mould set in an hour or so. Just doing 20mm to check all the calculations are correcrt. And the mould and insert mesh properly.
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JoergS Tiro Offline Weaponizing rubber since 2008. Posts: 33 Gender:	Re: The whistling sling balls of the Burnswark battleground Reply #10 - Aug 15^th, 2016 at 4:06am Great! Can't wait for the results.
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Re: The whistling sling balls of the Burnswark battleground
Reply #11 - Aug 15^th, 2016 at 6:45am

currently got a 20mm set and should be a 30mm on the machine. like an idiot I only measured the clay balls I like after startnig the 30mm mould.

So that's a 40mm I also need lol

Had a go with some playdoh on the 20mm - yeah that works. the hole is really small. Guess it works like blowing over the neck of a beer bottle or a set of pan pipes.

Don't be fooled by the large picture of the insert, in reality it's really quite tiny.

I'll take some pics later

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Re: The whistling sling balls of the Burnswark battleground
Reply #12 - Aug 17^th, 2016 at 12:57pm

pics of the 20mm and 40mm in playdoh.
They look a a bit out of round as they stretch when you remove them.

The hole on the 20mm looks bigger because playdoh dries out and shrinks, as it shrinks the hole gets bigger and i made that one yesterday.

I'll dig out the clay and make some slingable ones later.

20and40mm_800x252.jpg (45 KB | 207 )

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Bill Skinner

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Re: The whistling sling balls of the Burnswark battleground
Reply #13 - Aug 17^th, 2016 at 1:54pm

So, do they whistle?

JeorgS Normally, gravity does not have any effect on a projectile if it is launched in a perfectly horizontal trajectory. However, most of the time we launch, shoot, throw or whatever, we go above the horizontal and the projectile arcs up and then comes down. Gravity has a part in that. The faster the velocity and the closer the target, the less the arc over the horizontal line.

So, gravity does affect the trajectory, as does air resistance. And as you pointed out, usually air has a greater effect on a projectile, but it is lessened as the surface area of the projectile decreases, so air doesn't affect a lead projectile as much as it would a larger surface area, but equal weight, projectile.

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Curious Aardvark Forum Moderation Offline Taller than the average Dwarf Posts: 13965 Midlands England Gender:	Re: The whistling sling balls of the Burnswark battleground Reply #14 - Aug 17^th, 2016 at 2:27pm no idea - those are made of play doh You can't sling them. Can't get any sound by blowing over the hole, tried that.
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