BARREL TWIST RATES

Discussion in 'General Airgun Chat' started by blacklab, Dec 29, 2018.

  1. blacklab

    blacklab Active Member

    Joined:
    Aug 12, 2012
    Messages:
    651
    Location:
    pontypridd
    Club:
    nelson
    A youtuber made a statement and he said that airgun barrel makers have got it all wrong except one what are everyone's thoughts
     
  2. SteveC200

    SteveC200 Active Member

    Joined:
    Jan 19, 2012
    Messages:
    514
    Location:
    Colchester
    Club:
    Iceni Marksmen
    A link to the video perhaps? Otherwise my thoughts are that this thread has just wasted my time. ;)
     
    nemesis and dlloyduk like this.
  3. Jesim1

    Jesim1 Active Member

    Joined:
    Mar 23, 2016
    Messages:
    320
    Location:
    Wigan/St Helens
    Club:
    BOAC, BGC
    I'm no expert on this, but I can't help thinking that barrel makers are! Perhaps the guy you mention should stick to youtube? but also accept without questioning we don't improve.

    James
     
  4. AlexS

    AlexS Active Member

    Joined:
    Sep 10, 2013
    Messages:
    109
    Location:
    Germany
    Historical barrel twist rate development:
    - Can we use the same twist rate on the same machines we use for .22 l.r.?
    - Yes.
    - Are the barrels sufficient accurate?
    - Yes.
    - Stop development.
     
    cloverleaf likes this.
  5. blacklab

    blacklab Active Member

    Joined:
    Aug 12, 2012
    Messages:
    651
    Location:
    pontypridd
    Club:
    nelson
    if against the rules can mods delete
     
  6. simona

    simona Active Member

    Joined:
    Nov 26, 2008
    Messages:
    305
    Location:
    Lowestoft
    That's a good film but I think he's focused on very high power/long range performance. I'm not sure whether pellets shot at 11 foot pounds are significantly overstabilized at 55 yards.
     
    Lavant_Lad and garym like this.
  7. Nomads HFT

    Nomads HFT Well-Known Member

    Joined:
    Sep 27, 2015
    Messages:
    430
    Location:
    Worcester
    A friend compared a 1:17.7" LW barrel with a 1:39.4" polygonal barrel, and found the 1;17.7" grouped better to about 50 yards, but the 1:39.4" grouped better beyond. The pellets with the slower twist rates were better able to nose into the direction of their travel at longer range than the more spin stabilised 1:17.7"
     
    Last edited: Dec 29, 2018
  8. Paul_T

    Paul_T Active Member

    Joined:
    Jul 28, 2018
    Messages:
    111
    Location:
    Burnley
    I thought the same. Also looks to be promoting the FX smooth twist concept.
     
  9. Ballisticboy

    Ballisticboy Active Member

    Joined:
    Jan 4, 2019
    Messages:
    81
    Location:
    Maidstone
    I hate to be the bringer of bad news so soon after joining but the video talked about here is extremely bad containing, at the last count, 21 errors ranging from minor/debatable to complete nonsense. Even the picture used to promote it, as shown above, is completely wrong showing a total lack of understanding of even the basics of aerodynamic stability. I don't know who the author talked to before making this video (though I have my suspicions) but they obviously didn't know anything about projectile external ballistics or aerodynamics.
    As it happens, there are some arguments to be made for lower spin rates for longer ranges when using diabolo pellets in order to avoid dynamic stability problems. Gyroscopic stability is not a problem. The problems are worse at higher speeds and much longer ranges but they can occur in sub 12FPE guns at ranges around 50 yards, particularly if something, such as a wind gust, disturbs the pellet. Of course if twist rates are reduced then you are stuck with diabolo pellets and their associated poor ballistic behaviour.
    Much of the ideal twist rate will depend on the individual pellet design being used. I did carry out a modelling study once looking at the effects of twist rate on AA Field pellets.
     
    Waldo, Brian.Samson and Tone like this.
  10. RobF

    RobF Administrator Staff Member

    Joined:
    Mar 4, 2010
    Messages:
    12,750
    Location:
    New Forest, Hampshire
    Club:
    Parkstone Gun Club, South Dorset FTC, Southampton Buccaneers
    Was there any/much room for improvement?
     
  11. simona

    simona Active Member

    Joined:
    Nov 26, 2008
    Messages:
    305
    Location:
    Lowestoft
    Yeah, go on, don't leave us hanging!

    Fairly unscientific but I take comfort from the fact that many FT guns use barrels designed for 10 m shooting where the guns run at 6 foot pounds. This is just about the residual energy remaining in a 11.5 foot pound FT rifle at 55 yards. Plus my gun groups awesome.
     
  12. Ballisticboy

    Ballisticboy Active Member

    Joined:
    Jan 4, 2019
    Messages:
    81
    Location:
    Maidstone
    Not really. Twist rates from around one turn in 15 inches up to between 25 to 50 inches gave very little change in the size of error at the target. However, I was only considering one type of error source (offset pellet CG from the centre line) and one type of pellet using a full six degree of freedom model at ranges associated with airguns (50 metres). .177 seemed to be more sensitive than .22 in having a narrower optimum band but stilll around the same values i.e. one turn in 15 inches up to 25 inches or so.
    I would give a link to the threads I did on the results but since they changes their site none of the graphs are visible. I will have to try redoing it with the graphs visible somewhere.
     
    Waldo, blacklab and RobF like this.
  13. Ballisticboy

    Ballisticboy Active Member

    Joined:
    Jan 4, 2019
    Messages:
    81
    Location:
    Maidstone
    I have found the graph which summarised the results for .22 and .177. Each dot represents and individual data point. The pellet speeds represented a launch velocity for 11.5FPE in both calibres. The pellets loss in speed was computed using my drag law for the AA Field which is available in Chairgun as one of the alternative drag laws. Don't take too much notice of the fact that the .22 errors come out slightly less than those for the .177, that is merely a function of the size of the offset modelled.

    17722off2.jpg
     
  14. RobF

    RobF Administrator Staff Member

    Joined:
    Mar 4, 2010
    Messages:
    12,750
    Location:
    New Forest, Hampshire
    Club:
    Parkstone Gun Club, South Dorset FTC, Southampton Buccaneers
    That's pretty fantastic stuff, being able to model that.
     
  15. Nomads HFT

    Nomads HFT Well-Known Member

    Joined:
    Sep 27, 2015
    Messages:
    430
    Location:
    Worcester
    Miles (Ballisticboy) is the authority on airgun pellet external ballistics, Rob.

    If a bloke on the Internet says the manufacturers have all got twist rates wrong, and Miles says that actually, they haven't, I know who I'd believe.
     
    Last edited: Jan 5, 2019
  16. RobF

    RobF Administrator Staff Member

    Joined:
    Mar 4, 2010
    Messages:
    12,750
    Location:
    New Forest, Hampshire
    Club:
    Parkstone Gun Club, South Dorset FTC, Southampton Buccaneers
    What, you don't believe something that someones made a video about on Youtube? Whatever next... :D
     
  17. SteveC200

    SteveC200 Active Member

    Joined:
    Jan 19, 2012
    Messages:
    514
    Location:
    Colchester
    Club:
    Iceni Marksmen
    So we have one guy on the internet saying one thing and second guy on the internet saying its bobbins. Out of interest, what are your credentials second guy on the internet? ;)
     
  18. Tone

    Tone Active Member

    Joined:
    Apr 29, 2010
    Messages:
    773
    Location:
    Bristol
    Club:
    Bristol Aero & Nomads
    Welcome to the Forum Miles, dont worry about saying it as it is, your input is most welcome. Just try and keep the technical speak as simple as possible for us more pragmatic types :cool:
     
    RobF and Roger Pardy like this.
  19. blacklab

    blacklab Active Member

    Joined:
    Aug 12, 2012
    Messages:
    651
    Location:
    pontypridd
    Club:
    nelson
    Thanks for that someone who knows what they are talking about;)
     
  20. Ballisticboy

    Ballisticboy Active Member

    Joined:
    Jan 4, 2019
    Messages:
    81
    Location:
    Maidstone
    Right you asked for it, here it is. ;)
    Qualified with a degree in aerodynamics and worked in the aircraft industry on Harriers and Hawks. Left the aircraft industry (they didn't pay enough) and joined the MOD working in the gun external ballistics department. Spent the best part of 40 years working on projectile external ballistics design, testing modelling and theory becoming the recognised MOD expert on the subject of external ballistic data. Had to deal with all calibres and speeds of projectiles from 1 metre diameter (no prizes for guessing who that one belonged to) down to particle sized fragments from war heads with projectile speeds from 90m/s up to 10000m/s.
    For airguns began looking at pellets back in the late eighties and worked with the late Gerald Cardew on new pellet designs (I designed them, he made them) and advised on some of the book "From Trigger to Target". Managed to get some flare stabilised bomblets (which coincidently looked just like pellets) wind tunnel tested at around that time and used an airgun to set up tracking radar on small arms trials (much cheaper ammunition was the only reason, honest).
    And after all that I am at best an average shot. :confused:
    Well you did ask. :)
     
    Chalkie, Waldo, RichWafta and 9 others like this.

Share This Page

  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.
    Dismiss Notice