Jsb pellets

Discussion in 'General Airgun Chat' started by tony mccracken, Aug 2, 2018.

  1. retroruss

    retroruss New Member

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    I floated my ftp with a rowan kit after suffering poi shift but I couldnt get it to shoot well at all .I ended up getting the 2 piece carbon set and put the band back on. I fettled the stock slightly inside the front where the band was touching because with the orings removed you could see the band was touching the bottom of the barrel so with the orings in it was forcing the barrel up and also the cylinder was nearly touching the band. i adjusted the stock until the barrel was central in the band then put the orings back in, it performs very well now, so for me albeit after some tinkering the band works best. I only use it for benchrest Btw.
     
  2. TenMetrePeter

    TenMetrePeter 10 metre long member

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    I would say more like touching a guitar string half way along. It dampens slightly but also doubles the frequency by setting a stationary node, and more importantly reduces the amplitude of each half of the sine wave.
    Barrel clamps should be converted to barrel dampers IMHO. Many Air Arms rifles have the O ring ex factory.

    Experiment: fix a 12 inch ruler to a table and twang it.
    Now lightly touch the 6 inch point with two fingers and do it again.
     
  3. Yorkshiretea

    Yorkshiretea B Grade Bandit

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    Not great footage but...
     
    Last edited by a moderator: Aug 8, 2018
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  4. RobF

    RobF Administrator Staff Member

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    seems to do most of it's wobbling after the pellet has gone...
     
  5. bootneckbob

    bootneckbob Active Member

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    I'm with Tone on this as we both bought the LG110 HFT 2014 a few years ago and I floated mine while he kept his fixed with the tuning screw in place. I don't think we could say one outshot the other on the range or we saw POI shift to any degree. What I do know is when I bought my Challenge I wasn't going to free float it.
    I've said on the other thread running at the mo about barrel bands that I believe POI shift is more related to the environmental conditions and shooter as the rifle flexing. Some designs are particulary bad granted but on the whole. If you shoot the Steyr and tweak the tuning screw you can see the group open up and close. By not having the screw, and floating the barrel you might also see the best group the rifle can produce as many top shots would sign up to. Having just watched that slow motion video I wonder how much movement there is in a ally chassis which is bracing the barrel?
    It's all interesting stuff, but as someone else on here has already eluded to we'd do better to improve ourselves rather than doing the science, far too many variables.
     
  6. bootneckbob

    bootneckbob Active Member

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    One thing I would add though since starting to shoot FT fairly recently is the POI shift (for whatever reason) is more evident than ever before shooting HFT and I'm putting this down to shooting the extra 10 yards and shooting at x40 mag rather than x8. In the recent really hot conditions I've adjusted my scope with the same number of clicks to compensate as other shooters I know who have fully floated barrels.

    Oh bugger, I'm in the wrong thread now, cheers Tone!
     
  7. Tone

    Tone Member

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    Hi Rob, is the POI shift more evident with the fixed mag Leup Comp or the the variable mag Sightron?

    Just to confuse things even more maybe someone can come along and set up another thread with the title 'fixed mag or variable mag - which gives the greatest POI shift':confused:

    Certainly been a summer for some extreme temperatures :cool:
     
  8. bootneckbob

    bootneckbob Active Member

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    As you know Tone I've used quite a few scopes this season, least of all (almost) being the Leupold. I first noticed the high shots in heat with the falcon. This continued with the sightron but was also the same for many on the course as you listen to the chatter. One other shooter on here with a Leupold and 9015 was making the same corrections I was for the heat. This goes some way to demonstrate to me it's not the scope or the rifle but the conditions in general.
     
  9. RobF

    RobF Administrator Staff Member

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    You have 3 types of shift

    Physical shift : bending of the materials in the gun, usually the stock, moves the barrel relative to the scope.

    Mechanical shift : changing properties of seals and seats which affects the speed of the gun

    Optical shift : small changes in the scope mechanism which move the focus point

    Fwiw I’ve not seen mounts shift on any gun I own, adjustable or otherwise.

    Optical shift is unique to each scope model.

    I’ve seen physical shift on a free floated gun with a wooden stock because the cylinder wasn’t floated.

    Working out what to do means you need to work out what is happening first but I can understand wanting to remove possible hurdles before you run into them.
     
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  10. bootneckbob

    bootneckbob Active Member

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    Rob, surely there is a 4th with environmental? Agree with what you are saying in that there's a mechanical shift, physical and optical but the environmental which encompasses all three is also a factor? Ultimately POI point of impact is just that, it's where all the factors are combining to give you a point of impact. That will change unless the conditions are the same but then that would include wind. So really while I understand that want and desire to try and minimise those effects within the gun you still (and thats all of us not just you) will need to apply a correction to POA to get the POI where we want; that might be by clicks or aiming off.
    I'm not going to compare FT or HFT to my military shooting but we accepted that on a range day it would usually be check zero / POA and then crack on with the shoot. Recognising that if the POI was within a given parameter for the range then that gives you a POA to use. Basically aiming off for the conditions.

    This is still a thread about JSB pellets isn't it?? I'm 10.3 and have been for years but I have a shed load of 7.9 which I aquired for another rifle I no longer own. I've given them a little test against the heavies and whilst they were incredibly stable for drop at 55yds they were completely dispearsed horizontally almost in a perfect line. The heavies on the other hand were a mix of vertical and horizontal giving a more rounded and therefore smaller group. From what I've tried 8.4 wasn't better than 10.3 and the drop is only a tad less.

    Slightly tongue in cheek, I've had way more targets go down with a splitter at 10.3 than 8.4s; Tone can vouch for this! You could also argue that the 8.4 would have dropped in and not split at all.....

    As I'm running low on my last sleeve of heavies I am considering trying the 7.9s again and spending more time on Brians wind game!
     
    Last edited: Aug 9, 2018
  11. RobF

    RobF Administrator Staff Member

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    Yeh, there's wind.

    What I don't buy at all is this up down thing that others do. There maybe an effect, but not to the degree where you'd miss a target because otherwise we'd never hit them because we never know what the wind is doingto that degree or how we are shooting into it. If it occurs it's fractions of a mm. I put it right down the list of things to worry about. That said I know one of the top 3 does aim up and down for the wind direction.

    For ages I used a Kestrel meter to measure enviroment when the Walther was shifting (about 40mm at 55yds). I saw a correlation. What I didn't find was causation. Then I did. Although the enviroment was making the gun shift, what it was actually doing was making the wooden stock warp, which pushed the cylinder into the block, which moved the free floated barrel. Floating the gun entirely solved this. I think we always need to be careful when saying something has a cause and effect that we are sure we know the mechanism first.

    When I zero I only shoot lines. I haven't seen any noticable difference between 7.9s which I've shot for about a decade and 8.4s which I tend to only shoot in the springer. I haven't tried the old dog/new kid heavies. They're all the rage. Funny thing is, top 3 in GP series, one shoots heavies, one shoots 8.4s and one shoots 7.9s... and if that fact is anything to go by, they're in 1st, 2nd, 3rd place respectively... (but then there is only 1 target between 1st and 2nd)...
     
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  12. bootneckbob

    bootneckbob Active Member

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    So heavies are in vogue...interesting. I've been shooting them for the last 7 or 8 years. Guess if I'd been competing at the top level and winning they might have been back sooner! I say back, were they ever in? I always thought it was 7.9 or 8.4 in years gone by.
     
  13. Dale

    Dale Active Member

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    Yes.

    From around 1988-89 until approximately the mid 1990's the 10.5 grain Bisley Magnum and H&N Barracuda Match were the pellet of choice.
     
  14. bootneckbob

    bootneckbob Active Member

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    So the wheel has turned full circle then. Thanks for that Dale.
     
  15. Adam

    Adam Active Member

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    Any empirical data about on harmonics specifically for (sub 12) airguns?

    What is the resonant frequency of a typical airgun barrel, or, preferably a specific barrel on a specific gun/pellet with a chrono string and a mechanism to tune harmonics?

    Frequency gives us the period of oscillation. It should then be straightforward to map the distribution of muzzle velocities (should be a linear relationship between m.v. and barrel time) from a chrono string onto this value and see if it is possible to fit a useful chunk of the histogram into that time interval. That answers the question of is it even worth tuning harmonics in the first place.

    The next question is, is it possible to fine tune the frequency to that degree of precision? Or is it more generally, as I suspect, a question of unscientific tweaking. Shoot a group, tweak, rinse and repeat.
     
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  16. TREV RYN

    TREV RYN Well-Known Member

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    well you beat me to it adam i was gona say all that:)
     
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  17. Adam

    Adam Active Member

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    Translation: How fast does the barrel actually wobble, and can you set the barrel wobble speed so that most of your shots come out of the barrel in the same part of the wobble? Or does it wobble too fast? :cool:
     
  18. Conor

    Conor Never been banned from sales Staff Member

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    Your last two sentences is the answer
     
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  19. simmmo

    simmmo Member

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    Have put out a few courses and brought a few in, admittedly only at HFT ranges and I am afraid I will have to disagree. Have seen 45yd 35mm targets battered out of the top and significantly so. One from memory the ground was all flat from peg to target, target on a spike 3ft off the ground at the base of a 4ft berm a couple of yards behind it with a fair bit of helping wind. 90 people had shot at it with more than 20 out of the top. In my experience there would only be the odd random pellet out of the targets central band with most below centre. Equally once people started seeing the history high they would then start erring on the side of caution and shooting it short . So go figure. My theory would be the pellet being caught up in the airflow and following its course over the berm.


    When in South Carolina, very hot and humid, shooting benchrest few years back got the left to right pretty much right but kept missing high and low. We had normal wind flags blokes who won had ones showing vertical their cards had very little up and down dispersion with their left to right mimmicking ours. Admittedly it is benchrest so a small target at only 25 metres but looking at the match cards there was definately something going on.


    I don't allow for it but I don't dismiss it either. If I ever went back to benchrest I would invest in some flags showing vertical.


    Monkey
     
  20. simona

    simona Active Member

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    I don't understand how harmonic changes when switching from exacts to premiums could always result in premiums shooting to a lower POI. No sense in that that I can see. If there are harmonic differences causing POI shifts one would have thought they would be in any direction, not just downwards.

    I tried the first generation premiums which had the same external shape as an express but the weight of an exact. They dropped more than exacts from 25 yards to 50 yards. I cannot remember the exact amount as it was many years ago but in my particular gun it was over 1 MOA extra drop.

    Ripleys have an interesting barrel arrangement. Limited scope for vibration with that.

    It is a middle ground between floating (and dealing with harmonics) and fixing and dealing with potential shifts.

    There is no perfect system. It's a matter of finding something that works.

    A few years ago a had a really rancid system on my Dominator. I had an alloy tube with a 1mm clearence ID over the barrel. It was glued at the back and centred at the front with electrical tape. I was forever ripping this on and off and fiddling. It went though a stage of truly mega accuracy during which I noticed that the shroud was rattly at the front: it was just laying on the barrel. Despite the accuracy I couldn't live with this 'slap damper' and had to make it 'better'!
     
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