Aerodynamic Jump, different for pellets and slugs?

Forums Pellets, Projectiles, Slugs, & Ammo Aerodynamic Jump, different for pellets and slugs?

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    Centercut
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    I was giving this some thought these past two weeks when shooting both slugs and pellets into a wind that was from 10 to 11 o'clock and another day was from 1 to 2 o'clock. What I noticed confirmed the theories I've been studying. When shooting in winds from the 10:30 direction, the pellets would rise slightly more than predicted and the slugs would drop more. and conversely when shooting with winds from the 1:30 direction, the pellets would drop more than predicted and the slugs would rise more. By "predicted", I mean the calculated drop in a ballistic calculator.  I was doing this testing at 110 yards with .22 JSB RD Monsters and NSA 20.2 grain HP DB slugs.

    After watching Dubber's videos, I'm thinking that is due to the difference in the center of gravities between the pellets and slugs.  Has anyone else noticed this distinct difference between pellets and slugs in a quartering wind? 

    • This topic was modified 6 months ago by Centercut.
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    Therealld
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    A fairly little known fact is that most diabolo type pellets do the apposite with respect to "positive and negative lift" with crossing head winds compared to bullets.  I assume its due to the fact airgun pellets are drag stabilized to a large degree by design, while bullets are not, and pellets tend to fly sightly nose down, while bullets, due to typical shapes are tail heavy and fly nose up.  The wind is more likely to steer the pellet nose into it, and often causes a bit less drop on target with crossing right winds.  Not certain of the exact reason, but know by observation that pellets do strike higher or lower depending on wind crossing direction, and have observed that very few shooters are aware of this effect.

    Chairgun , so far as I know, still gives same poi drop with left or right winds, prolly due to lack of knowledge.

     

     

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    nomojo65
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    Therealid is correct, For example pellets go LOW in a right to left and HIGH in a left to right!, bullet shaped projectiles just the opposite “ from a right hand twist barrel “

    • This reply was modified 6 months ago by nomojo65.
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    oldspook
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    nomojo65

    Therealid is correct, pellets go LOW in a right to left and HIGH in a left to right!, bullet shaped projectiles just the opposite “ from a right hand twist barrel “

    Would you please cite your source on this?  I'd like to read up on it.  Thanks.

    NVM found it:

    https://hardairmagazine.com/ham-columns/vertical-deflection-for-pellets-in-crosswind/

    Something new every day.  I knew of the aerodynamic effects of a cross wind but did not realize that diabolo (seriously that word SHOULD be in the spell checker on an AG site 😉) flew differently from a spitzer shape.

    • This reply was modified 6 months ago by oldspook.
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    nomojo65
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    Honestly I learned the hard way I used to shoot short range C.F. Br and learned the vertical jump for bullets “never paid much attention” to AJ because it was short range! Then started shooting Airguns and couldn’t figure out why my flags were saying one thing but pellets were doing something else? Then one day I stumbled on to Mike Niksch’s wind deflection pie chart and saw that every thing from quartering to 90deg deflection was almost completely opposite to what I was correcting for by my flags! After talking to other 25m shooters they confirmed what I was seeing on paper… I don’t really know the science around it? Theralid explains the physics of it pretty well

    • This reply was modified 6 months ago by nomojo65.
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    oldspook
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    Had a big argument once with the CEO of ATN about whether or not Coriolis was important to calculate in his ballistics software.  He maintained it was not because some fellow who was doing most of his testing told him it wasn't important at "short ranges".  Tried to make the point that it wasn't about range but about time of flight but … no joy.  That was three or four years ago.  'course it becomes a constant (Coriolis) when shooting BR matches so I suppose there is a point in there somewhere.

    I believe I had read of this difference between bullets and pellets but I have not reviewed the literature in at least a couple of years and details get fuzzy when you are not always working with them.

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    JamesD.
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    http://www.appliedballisticsllc.com/Articles/ABDOC101_2_ExtendMaxEffectiveRange.pdf

    https://youtu.be/tfwwflFQDHw Aerodynamic jump.


     

    https://youtu.be/B_0ck6EvF3I  wind as a wall.

    I don’t think it matters with pellets in no wind at low speed/close distances. 
    If you’re shooting long range, pellets or slugs yeah, wind is going to affect your outcome.

     I only know this about slugs. I’ve wanted a bit faster twist barrel with no choke and shallow grooves since I could see a .004” gap of light, blow by air, and LW 17.7 is too darn slow. Yet somehow the dang thing loves 28.9-32 grain best for me. It handled .435” OAL heavier slugs but not as well. 
      I haven’t seen slugs shot from any airgun filmed at high speed but firearms bullets can come out doing a jig. Some like 215 grain hybrid ELD 06 don’t even settle down till 200-400 yards, but they’re still going 1100 at 1900 yards. 
      I don’t know what you guys are using but I don’t like our airgun barrels for slugs. I’ve made hits past 400 yards with 28.5-32 grain .22’s but my stock barrel is not meant for slugs. If any yaw occurs I believe it’s from insufficient spin rate instead of sheer massive speed, SG RPMs wanting to tear itself apart until it settles down and flies straight. 
     

    @centercut. If your theory is based on balance point you’d be interested in the fact that Dave Corbin has provided 4mm-4.5mm perfect hollow delrin spheres to displace weight in swaged slugs. Anywhere from 5-7 grains is displaced by one of these roughly 0.9-1.1 grain balls. 
    They can be put anywhere to keep your nose flatter or up further. For short range near top to middle of a HP they are driven in & act like a piston. 
      

    • This reply was modified 6 months ago by JamesD..
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    nomojo65
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    I reread your post again CC and see what your saying about exaggerated jump in slugs and pellets in quartering winds? I have no explanation for that phenomenon, I can see the exaggerated difference with pellets because of the extreme arc of flight? Just a guess!

    • This reply was modified 6 months ago by nomojo65.
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    Centercut
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    @jamesd. Your charts show the expected drift and jump for slugs, not pellets. The aerodynamic jump for pellets is the opposite of slugs as LD @therealld pointed out above.

    From the Hard Air Magazine Technical column

    With a spinning projectile, the center of gravity (CG) and the center of pressure (CP) seldom line up. In fact the CP moves as the velocity changes. Diabolo pellets are designed with the CG forward of the CP to give them “shuttlecock stability”. When the pellet exits the muzzle, and runs into a crosswind, it tends to turn into that crosswind.  However, pellets in crosswind react to the side force by pitching up or down, depending on which way it is spinning and which side the wind comes from.

    Slugs (bullets) are designed with the CP forward of the CG, so they experience the opposite "jump" from the diabolo pellets.

    • This reply was modified 6 months ago by Centercut.
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    FredAZ
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    "Chairgun , so far as I know, still gives same poi drop with left or right winds, prolly due to lack of knowledge."

     

    Yep — don't fall into that "there's an App for that, so it must be right" trap.

    Chairgun and the like are NOT the gospel on ballistics.

    And yes, Coriolis DOES matter – different directions during sight-in and shooting need to be accounted for – the earth rotates at ~1000MPH.

    • This reply was modified 6 months ago by FredAZ.
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