Drifting with the Breeze

Discussion in 'General Airgun Chat' started by blueboy, Dec 1, 2015.

  1. blueboy

    blueboy Member

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    Hi just thought I would start a new thread, and get others views on this, more than likely this has been covered before but here goes anyway.

    We here Guys saying my rifle carries more wind at distance than this or that rifle, when I here this the old grey matter starts ticking.

    When you consider how many air rifles must be fitted with Lother Walther Barrels, and some with CZ barrels,
    Lets take the Walther ones first.

    If you have two rifles of different manufactures but both fitted with Walther barrels, and both doing say 780 FPS, same pellet there should be no difference in how much the pellet at the other end is carried by the wind.

    Now are different manufactures asking for different twist and the number of turns in the barrel length they request.

    When a barrel is made to possibly a standard length the rifling is a standard 2.5 turns from the breech to the muzzle, I am not saying it is because I do not know how many turns they are made with, but some rifles do have that, now lets say that length is 16 or 17 inch long, yet one manufacture cuts their barrel down, so less twists in the barrel, so the pellets has a different spin ratio to the longer barrel, this may be the reason why some say their rifle carries more wind.

    When you look at the same rifle made yet you say to yourself how can the others have problems with the shooting the same pellet as me, its all over the place, this brings us back to different batch numbers of pellets, which someone will no doubt raise.

    I wonder if using a shorter barrel causes different problems with the pellet than a longer barrel, take a GC2, they were fitted with a long barrel and I have had two plus the ones I know of and not one has suffered from accuracy problems like we are getting today, does this shorter barrel which needs more volume of air to get the same speed is this the reason which affects the flight of the pellet, where as a longer barrel needs less air because its in the barrel longer, I know some will say it the choke which has the effect, but it just makes me wonder.

    I hope this debate raises lots of views on this subject, and don't for get this is just a thought on my part, some may have carried out test on various barrels, of different lengths.

    I hope you will excuse my English I have problems in how I lay my words out, but the crux of this is here, enjoy the debate don;t get wound up.
     
  2. DEAN C.

    DEAN C. Steyr Convert

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    Too many variables....... and no barrel or batch of barrels can be identical even if the same length and choke.

    Different guns deliver air in different ways as well so it will differ how one gun will push the pellet out. Some regs or valves will give a smaller volume quicker and with a higher pressure burst, where others will give a lower pressure, bigger volume push that builds gradually.
    A longer barrel uses air differently because it needs less air as the pellet stays in the barrel longer, allowing air to build up behind it and gain speed. That's why longer barrels use less air.

    What you can generally say, is that most modern similar guns with the same type of barrel usually like similar batches of pellets. How vague is that?:rolleyes:

    Wow what was the question again?::confused:
     
  3. RobF

    RobF Administrator Staff Member

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    Not worked it out yet.

    Same gun, we've tested long, short, medium. What appears to be the case (and it's really early days) is that some barrels prefer a shape of pellet, and some prefer others. I've got one pellet which goes well in all, but I'm waiting to see the variation across batches before saying it's wonderful.

    BC is what gives you the wind drift, but i'm not seeing any correlation with precision, just accuracy. The worse the BC, the worse the drop. But in reality it only adds about 1 MOA to a group. However between the best and worst of a pellet I've seen 2 MOA at 55yds.

    [​IMG]

    So I think it's more to do with shape, shape giving BC, and shape fitting the barrel.

    Between the barrel brands there is a lot of variation in the shape of the lands and grooves. And also the tightness of them, and that tightness relative to the choke.

    Theories. All good fun.

    Your English seems pretty good. But we do excuse the Midlanders a little anyway :D
     
  4. Brian.Samson

    Brian.Samson Allowed in Sales Staff Member

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    Don't assume that a pellet is the same shape coming out of the barrel as it is when you put it in.
     
  5. RobF

    RobF Administrator Staff Member

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    No, even with just rodding you can see some barrels bit much deeper than others.

    One thing that does need to have care taken is collecting a shot pellet. If there's a rapid deceleration the tail can bunch towards the head which can lead to the assumption that the skirt is being blown out. Collection much further down range, when the pellet is falling natually doesn't display it. Even at 55yds pellets will deform on impact, they're still travelling at 600 fps. However toothing is deeper on a full power shot pellet than on a not shot.
     
  6. Brian.Samson

    Brian.Samson Allowed in Sales Staff Member

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    I've seen some photo's of shot pellets (carefully collected) and I know the common belief is that the skirt will open out and the pellet will be squashed slightly, but I've seen some photos where the pellet can actually elongate - I think it was certain dies of CP's that did this, but who knows it might also apply to certain batches of JSB's as well.

    The air delivery system plays a big part in the resulting BC of a pellet, it's not just the barrel and MV.
     
  7. Tench

    Tench WHFTA World Champion 2016.

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    The gyroscopic stability of a pellet created by the twist rate has an effect on the pellets resistance to be deflected by external forces, wind and gravity. This is the principle of a rifled barrel. Changes in the twist rate can give the impression of a different bc without actually changing the bc. But the bc can be affected by a multitude of variables, inc;

    Barrel length
    port area
    port length
    valve duration
    reg pressure
    reg volume
    hammer spring preload
    hammer weight

    I have also found that a twist rate can suit one pellet and not another, with some undesirable effects (magnus) occurring with certain combinations. Centre fire shooters are very aware of the need to match the two.

    I have spent some time with this over the years , there are benefits to be had! :cool:
     
    Last edited: Dec 1, 2015
  8. verminator

    verminator New Member

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    I'm not sure how much airguns are meant to rely on spin stabilisation, but since the twist rate is similar to powder burners, it could well play a big part. Too much spin and the drag from the skirt is fighting the gyroscopic forces, particularly at long range. The equations indicate the length of projectile is a factor.

    Many people have commented on how their results have been affected by wind at distance. Shooting the heavier caliber, since they are slower, I have seen certain pellets suddenly carried off by the wind beyond 40 yards or so.

    I hypothesise a new theory: As the pellet travels further, the spin rate slows too and like a spinning top, it gets to the point where it starts to wobble and lose stability. How quickly it slows depends on the initial twist rate, velocity and BC. How quickly it destabilizes depends on how quickly it slows and the pellet length. Possibly other factors too.

    Some day, experimentation with high speed film cameras in controlled conditions may provide more insight.
     
  9. Deleted member 4175

    Deleted member 4175 Non member

    i would have thought you lot all knew by now the answer is simple
    its just a bit of VOODOO :D
     
  10. Conor

    Conor Never been banned from sales Staff Member

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    So what was your hypothesis again?
     
  11. Darron

    Darron Reformed Bandit

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    Hi Blue have you thought it might be time to change your gun?:D
     
  12. blueboy

    blueboy Member

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    spin

    Hi mate think you might be right barrel nearly worn out after nearly tin of pellets :D
     
  13. NeilM

    NeilM Well-Known Member

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    Compared to others, my experiments on this matter have been different and a bit cursory.

    I noticed excellent accuracy but massive wind drift on the very first LG100's, back in 2002. Borrowing a microscope, I rodded pellets through several 'barley twist' barrels and found severe damage to the pellets caused by the sharpness of the lands pulling pieces off the pellets and sometimes ripping the skirts.

    Obviously the damage on a pellet accelerating to 780 fps would be different, but never the less the very sharp lands would be having an effect.

    I managed to reduce a little the wind drift by working on the barrels to reduce the land sharpness, but the barrels were hard and I didn't want to get aggressive, as it is pretty easy to go too far and ruin a barrel.

    The very first EV2's had a similar issue with the CZ barrels, which is the reason AA changed to WL barrels. I was supposed to be sent some 'rejected' barrels to experiment with, but the whole thing fizzled out in the end. Shame really, it would have been interesting to experiment.
     

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