A rifled slingshot gun?

Discussion in 'New project ideas' started by JoergS, Nov 3, 2013.

  1. JoergS

    JoergS Administrator

    5,803
    109
    63
    Lots of people asked me if it was possible to give slingshot ammo (steel balls) some spin. That is of course not easy. The most obvious way would be to use a rifled gun barrel and push the ammo through it with a dowel.

    But. But but but.

    The dowel takes away a lot of energy.
    The dowel would have to be stopped, and it would have a lot of momentum.
    You can't squeeze a steel ball through rifling.
    The steel ball would be rather slow in comparison with a firearm bullet, so the rotation would be slow as well.

    How to solve it?

    Forget the dowel and the barrel, I just use a regular slingshot crossbow, much like my winch operated hand cannon.

    My idea is to rotate the whole slingshot gun. Based on Thorsten Dr. b. c.'s input during the "Galileo" filming here in Burgkunstadt, I just ordered a thick plastic tube (diameter 25cm), 1 meter long, and six rubber wheels for furniture pieces. All together under 20 Euros.

    The plan is to set the wheels up in two "rings", one at the front and one at the back of the plastic tube, and rotate the whole thing by means of a power drill, using some Thera Band as a transmission belt.

    The trigger will be a centered rod that is pulled by a wheeled hook from the outside of the weapon.

    The whole slingshot crossbow is inside of the tube, spinning madly (at 3,000 RPM). If the end speed of the bullet (20mm steel ball) is 50 m/s, this means it would spin once per meter.

    If I type in my parameters into this calculator

    http://www.bergerbullets.com/litz/TwistRuleAlt.php

    then the output says that the SG (stability factor due to the "Miller Twist Rule") is 2,47, which is truly excellent. Values over 1,5 mean "comfortable stability".

    [​IMG]

    I don't really know how to compare the results - as we all know, round balls need no spinning. But it will be an interesting contraption.
     
  2. kineticweaponry

    kineticweaponry Senior Member

    280
    1
    0
    Wow, i would of never thought of that soloution
     

  3. slingpit

    slingpit Slingshot addicted

    1,606
    1
    0
    Doesn´t give the twist style at PFS shooting a spin to the ball?
    But not as high, as with your construction.
     
  4. JoergS

    JoergS Administrator

    5,803
    109
    63
    Even if the 90 degree twist fully transfers to the ball (which I doubt), the rotation would be slow.

    A 120 cm draw (half butterfly) means that a full 360 degree rotation takes 480 cm (almost five meters, or 189 inches). SG would be 0,11 - way down in the unstable area.

    Even if you shoot a small bullet (say 10mm) at a higher speed (75 m/s) with a short draw (corner of mouth), we are talking unstable. Even worse, the SG goes down to 0.06 due to the lightweight bullet.

    So forget twisted bands if you want spin for stabilization.
     
  5. JohnKrakatoa

    JohnKrakatoa Loudest boom on Earth

    1,287
    0
    36
    this sounds epic. cant wait for the video
     
  6. Moin moin,
    eine Umdrehung pro Meter währe OK .... bloss bedeutet das bei deinen üblichen Entfehrnungen ...... 3-6 Umdrehungen ....

    Um zu sehen, ob es von der genauigkeit, oder ob es sogar eine verstärkung, oder abschwächung der Ballistischen Kurve bringt .....
    Währe eine grösst mögliche Entfehrnung schöner ... also aussendreh....!
    -
    Ist die Bohrmaschiene kräftig genug? wenn nicht Oberfräse (würde ich an deiner Stelle eg mal zulegen, gibt viel schönere Kannten, bei dehn schon Tollen Teilen, die du baust ... sozusagen, das i Töpfelchen.... (bis auf deine Handzwillen, die sind nicht mehr zu verbessern))
    Oder Autopolierer oder sowas, was einen Kräftigeren Motor, bei Akzeptablen Umdrehungen hat....
    -
    Habe ich das jetzt Richtig Verstanden?
    Ein 'Rohr, in dem die Latexbänder laufen, - ein Rohr, weil sonst die Flugkräfte sie zu weit nach aussen dehnen würden.
    Das Rohr aussen mit jeweils 3 Rollen voren wie hinten gehalten. Eine Rolle angetrieben, die die Umdrehung auf das Rohr überträgt - es also zum drehen bringt.

    Auslöser, könnte man event. auch über eine Schnur machen, an der man zieht ..... die 4000 Umdrehungen, bis man an der Schnur zieht, schadet der Schnur wohl nicht..... Auslöser dann sowas wie die Teile beim Sportbogen, so wie ich es auch an meiner Sniper habe....

    Die Kugel, müsste nur vorher Zentrisch festghalten werden..... Könnte man es mit dem Durchschleudern, durch ein Blatt Papier Kontrolieren, ob sie auch das Teil mittig verlässt? (Bloss doof mit den Latexbändern...)

    Naja bastel mal, hat ja bis jetzt immer Funktioniert... und vom wissen immer noch was zum Schleudern beigetragen ...

    Ach ja, Danke für das erwähnen..... meinereinerseits .... ich bin aber nicht der Schuldige, falls es nicht so hinhaut!!!

    -
    Ach ja... so Motoren, habe ich da... falls du welche benötigst.......
     

    Attached Files:

  7. Ghosth

    Ghosth Over the hill but still swinging!

    975
    1
    18
    Easier to put fletching on the ball I think!
     
  8. Withak

    Withak aka Whitehawk!

    4,700
    2
    38
    Well, this will be an interesting experiment. I'll look forward to the results.
     
  9. JoergS

    JoergS Administrator

    5,803
    109
    63
    ?
     
  10. Withak

    Withak aka Whitehawk!

    4,700
    2
    38
    Same for me - ???

    Are you thinking about cutting the rifling grooves into the ball, kind of like a Foster slug in a shotgun?
     
  11. Cadman

    Cadman New Member

    74
    2
    0
    Joerg, the rate of twist is slower for black powder weapons than the rate of twist for smokeless powder weapons. So shouldn't the rate of twist for a slower weapon like a slingshot be a slow rate of twist? Maybe 1 in 60" for example?

    Regards,
    Brian
     
  12. JoergS

    JoergS Administrator

    5,803
    109
    63
    That wouldn't work, air resistance at slingshot ammo speed is way too low to cause a significant twist.
     
  13. JoergS

    JoergS Administrator

    5,803
    109
    63
    I think black powder weapons use heavier balls (= larger calibers) and the muzzle speed is lower, hence a slower rotation is sufficient for an SG value over 1.5.

    The SG formula is simply based on laws of physics and has nothing to do with the propellant.
     
  14. Cadman

    Cadman New Member

    74
    2
    0
    I did not explain myself very well. I meant that smokeless powder usually produces higher pressures and higher velocity. I also meant that black powder produces lower pressures and lower velocities. Which is why the black powder weapons use a slower twist. I think that the slingshot will produce even slower velocities than either of the powder weapons. So I thought that an even slower rate of twist would be required for the slingshot. But I am only thinking out loud, and tossing in my two cents. Your practical experiment will be the judge.

    I routinely twist the bands on my draw, so I suppose that induces a twist on the ball. Would I be accurate in saying that my 1/4 turn in 32 inches, equals 1 turn in 128 inches?

    regards,
    Brian
     
  15. RegulusRubber

    RegulusRubber Junior Member

    77
    0
    6
    I think the necessary spin depends on how long a bullet is compared to it’s diameter. Long bullets needs the highest spin, round balls need no spin. One of the latest developments in Muzzleloaders, the Schweitzer Feldstutzer 1857 (my favourite model) uses 10,4 mm calibre with long Compression-bullets. It needs and it has a fast spin. I think it has the fastest spin of all Muzzleloaders.

    A dream https://www.egun.de/market/item.php?id=4616249&PHPSESSID=138c
    https://www.egun.de/market/item.php?id=4555137&PHPSESSID=138c#img
     
  16. JoergS

    JoergS Administrator

    5,803
    109
    63
    Yes, IF the twist transfers perfectly well onto the ball. I am not sure about that, though. At some point the bands will loose some draw force, then the friction between pouch and ball may not be high enough anymore.
     
  17. JoergS

    JoergS Administrator

    5,803
    109
    63
    Well, round cannon balls are a lot more accurate when fired from rifled barrels! Same for muskets. So even round balls benefit from rifling.

    But I agree in general, the shorter the projectile (in relation to its caliber), the less important is rifling. The SG calculator therefore wants both caliber and bullet length as input. The fact that I will be using balls, not torpedo shaped bullets, greatly increased my SG factor.
     
  18. RegulusRubber

    RegulusRubber Junior Member

    77
    0
    6
    Sorry, I wouldn't like to spread a bad atmosphere but, for the rotating slingshot the spin of the ball would be slow. The technical effort is very high. Alone the barrel for the ball must be centered absolutely.
    Only 1 mm of unbalance and the ball flies around the corner.
    Because a ball needs no spin it would be more precisely without the equipment.
    Therefore the efficiency is zero at once.

    However, all this would not care if the fun factor would be high. But then it must work as it shall and I doubt that it will. :(
     
  19. JoergS

    JoergS Administrator

    5,803
    109
    63
    All true. But I will solve the technical problems (that is actually the fun part). I will make the position of the ball finely adjustable, so that it will be perfectly centered in the end. I have my high speed camera, which is a great help for such fine tuning.

    Yes, the technical effort is enormous, and yes, the result won't be worth it. But don't forget that I run an entertainment channel and not a company that needs to develop serious products. So I have to look at the entertainment value of my projects, not at technological and commercial goals.

    Will the views I can get for this project justify the efforts? You never know, but the potential is there. People love crazy scientific experiments.
     
  20. kiitos

    kiitos Banned

    224
    0
    0
    That not will work. The bullet is too slow.
    Nobody would be abled to measure more precision depending:
    the archer represents the biggest problem. Error code 75.
    75 cm.s behind the "muzzle."
    With all his faults of releasing it's senseless to track that any further.
    Better would be to reflect a three-point releasing with no chance
    rubber to come out "diagonally"/ marble initiated to be let off slanted.
    You only must remember: a shotgun hits long distances because of the
    number of charged lead. There's no muzzle spin, they have a "choke!"
    The second is: arrows are fletched with an angle of somehow 1 degree.
    Now calculate the rotation on 10 m.s?
    An arrow currently must be tuned to the received energy-
    best is to hit the target without any vanes as well as with them!
    All in one it's the result of set arrow weight in a relation to draw
    length and short (1/67 sec) impulse (carbonaries.)
    Bow technic is the art to stabilize and center the raw shaft.
    It's a fact. Centered totally.
     
    Last edited: Nov 3, 2013