# Parabolic curve over 20m and setup to avoid



## sp33db34n (Oct 17, 2017)

Hi all, I hope this question makes sense! so as I have the correct zero aiming points for hunting is there a combination of say steel 12 mm ball and band setup up that gives a flat trajectory over say 15m? I.e. what I would like to do is be able to get accurate over say 6/7m as that is my practice space and ten know I'll still be accurate using the same refence and anchor points (taking into account the target reduces in size) over 15-20m as by having a setup that has a flat (and kill) trajectory.

Thanks folks

Steve


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## KawKan (May 11, 2013)

Well, if I didn't say it before, welcome to the forum, mate!

What you have in mind is easily plotted in the powder burner world. But in that universe you have standard bullet weights and muzzle velocities to work from. In the slingshot universe, we have latex.

Latex performance varies with thickness, width, taper, temperature and hysteresis (length of hold in this case). I suspect this is why the parabola you describe is not common knowledge in the slingshot world.

Instead, we work with some givens:

1. Higher velocities produce flatter trajectories and less change in elevation over distance.

2. With a given bandset and ammo combination, elevation changes for range can sometimes be observed and recorded as marks on the fork or memorized changes in anchor point height.

Good luck, and good shooting!


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## kevmar (Aug 5, 2017)

/\ Interesting post KawKan,

so in effect once you find the set up that suits you,

then stick with that and get used to it inside and out ?


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## sp33db34n (Oct 17, 2017)

kevmar said:


> /\ Interesting post KawKan,
> 
> so in effect once you find the set up that suits you,
> 
> then stick with that and get used to it inside and out ?





KawKan said:


> Well, if I didn't say it before, welcome to the forum, mate!
> 
> What you have in mind is easily plotted in the powder burner world. But in that universe you have standard bullet weights and muzzle velocities to work from. In the slingshot universe, we have latex.
> 
> ...


Thanks for the welcome!

I have used the 'ChairGun' app on google play which is geared towards airguns but will still give me the curve I need but for inputs I need the FPS or FT/LB which short of getting a chrony are hard to calculate! There is the band strength calculator by Jorg Sprave here http://www.slingshotchannel.com/band_calc.html but it doesn't output ft/lb or FPS. Going by his description however of how the calculator maxes out at 18kg draw weight I was able to do a rough conversion of a max set up to FT/LBs and then able to use this to work out the curve. To be honest it's a bit of a faff and was wondering if there were any existing FPS / FTLb calculators out there or should I just bite the bullet and by a chrony?


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## KawKan (May 11, 2013)

There are many approaches and solutions to most things in life.

Most of what I learned about flatbands could be applied to tubes, and vice versa.

By approaching slingshots with an active and open mind, we can make observations about our results and apply them in future sessions. It's just building a body of knowledge to use on our journey.

LOL! I'm pretty full of it today!


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## sp33db34n (Oct 17, 2017)

kevmar said:


> /\ Interesting post KawKan,
> 
> so in effect once you find the set up that suits you,
> 
> then stick with that and get used to it inside and out ?


Thanks and yes that was the plan! or have 2 identical frames one with a weak band and plastic 12mm ammo and the other with hunting strength bands and 12 mm steel so I can use the former indoors but use exactly the same 'shape' as the other when switching to outdoor. The problem is without a lot of expensive trial and error work out I was wondering if there was a way to calculate which weak bandset+ammo gives the same zero points as a strong bandset and ammo.


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## KawKan (May 11, 2013)

I don't think you need a chrony.

If you are shooting well enough to make a reasonable group, try this.

Hang an A4 sheet of paper with a target circle near the top in your catchbox. Place a group near/in the target at 10 meters.

Use the same point of aim from 20 meters for a new group (oh, it will probably spread). Measure the distance between the approximate group centers and you the drop over that distance. Those are two points on you parabola. You may plot as many points as you like in the same fashion.


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## sp33db34n (Oct 17, 2017)

KawKan said:


> I don't think you need a chrony.
> 
> If you are shooting well enough to make a reasonable group, try this.
> 
> ...


Ha yes! that would work. My only other issue is that my outdoor set up would be powerful bands with 12mm steel but I don't fancy firing that off at 7m indoors so would like to practice indoor with proportionately weaker band+ammo and get the same reference point. Is it possible to work that out or am I worrying about nothing if I have a good indoor catch? And thanks for all the help BTW!!


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## KawKan (May 11, 2013)

sp33db34n said:


> KawKan said:
> 
> 
> > I don't think you need a chrony.
> ...


Try establishing your "sight picture" with the power set up outdoors.

Then move to your indoor set up and vary your band length to see if you can find a combination that comes close to the result on your outdoor set up. An exact match is iffy, but hey, these are slingshots!


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## kevmar (Aug 5, 2017)

12 mm seems like a lot to me,I have 9mm,and 6mm steels.

I use 6mm more than anything,they go straight through a drinks can at 30 ft.

For practice why not try these ceramic baking beans? About £4 per tub of loads.


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## kevmar (Aug 5, 2017)

Baking beans.


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## kevmar (Aug 5, 2017)

sp33db34n said:


> KawKan said:
> 
> 
> > I don't think you need a chrony.
> ...


You can get plastic practice balls.


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