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Good news Massive .177 JSB Pellet Velocity Test - 0-50 metres

Discussion in 'Anything Airgun Related' started by cloverleaf, Feb 4, 2014.

  1. cloverleaf

    cloverleaf Super Moderator Staff Member Mod/Admin

    Likes Received:
    Right, this is going to be a big one - even by my standards :p

    I managed to get up the club a while ago and carry out some pellet velocity tests at range. I'll try and summarise it all as concisely as possible..


    To test the velocity of a range of .177 JSB-manufactured pellets of different mass, at various ranges up to 50m to identify trends in drag, velocity & energy retention, velocity & energy variation, as well as to calculate Drag Coefficient (cd) and Ballistic Coefficient (bc).


    Rifle: Welham-regged Air Arms NJR100, .177
    'Scope: Hawke Sidewinder 4.5-14x42
    Mounts: B-Square fully adjustable 2-piece, allowing the 'scope to be almost optically centred
    Pellets: Falcon Accuracy Plus (7.34gn), Air Arms Express (7.88gn), JSB Exact (8.44gn), JSB Exact Heavy (10.32gn), JSB Exact Monster (13.47gn). All pellets 4.52mm head size.
    Pellet Scales: Unbranded digital units, 0.02gn resolution
    Distance Measurement Device: Wickes 50m surveyor's tape
    Rifle Rest: Allan 2-pc unit packed with magazines to adjust height, sat atop a big steel bench-rest
    Muzzle Chronoscope: Combro Mk4
    Range Chronoscope: Chrony F1 with polycarbonate guard
    Range Chrono Tripod: Unbranded cheapo Chinese ebay special
    Target: Steel target holder and large paper targets with multiple 6mm diameter aiming marks

    The pellets; left (lightest) to right (heaviest): Falcon Accuracy Plus (7.34gn), Air Arms Express (7.88gn), JSB Exact (8.44gn), JSB Exact Heavy (10.32gn) and JSB Exact Monster (13.47gn)




    The pellets were weighed and sorted into batches of 50 representing the mean mass of each type, with an extreme spread of less than 1% of the pellet's mean mass (so a 7.88gn pellet would have a mass variation of less than 0.08gn).

    The rifle was set up approximately level on an outdoor bench rest, with the Combro chrono mounted upside-down on the muzzle and the F1 Chrony mounted on a tripod directly in front the Combro.

    Five shots from each of the five different types of pellets were fired through both chronoscopes together (a total of 25 shots) and their velocities noted.

    The F1 Chrony was then moved out to 5 metres from the rifle's muzzle and a series of sighting shots (with unsorted pellets) fired at the target to ascertain the point of impact (POI) of the different pellets. Using the appropriate points of aim a second series of 5x5 shots were fired through the chonoscopes and their velocities noted.

    This process was then repeated at ranges of 10, 20, 30, 40 and 50m, with the rifle being refilled with air when appropriate.

    Sorted pellets:


    Initial chrony setup:



    The (very useful!) 12mm polycarbonate guard on the front of the F1:





    • The velocities for each 5 shot string at each range were averaged to obtain a mean velocity at that range.
    • The extreme velocity spread for each 5 shot string at each range was calculated for each pellet.

    From these values many other figures could be calculated for the pellet at each range - including:

    • Kinetic energy
    • Kinetic energy extreme spread
    • Time of flight
    • Drag force
    • Drag coefficient
    • Ballistic coefficient

    It was planned to use a correction factor for the Combro figures in an effort to calibrate it's output to that of the F1. Since my previous use of the Combro a certain amount of calibration had already been done (output value increased by 0.75%).

    On the day the readings of the Combro were so close to those of the F1 (the worst mean velocity difference was less than 0.4%, most were less than 0.15%) that no correction factor was used.
    The testing alone took the best part of 4hrs; not helped by the fact that the F1 had been left on; draining the lovely high-capacity rechargeable PP3 I'd bought expressly for the purpose and forcing me to set my morals aside and procure a disposable alternative from the nearest service station..

    In addition, after all the movement required to read and reset the Combro after each of the 250-300 shots taken I bloody ached afterwards! Conducting and writing up this test has pretty much swallowed an entire weekend and then some :p

    I had started writing this up as a full-fat scientific report, however I figured it might be a bit heavy going for some and tbh after the 3000 word mark got a bit sick of writing it (especially after considering that it's length might put people off).

    To this end I've tried to boil it down as much as possible; leaving out the stuff that's already widely known or of little interest.

    What I was Expecting....

    As pellet mass increases from the lightest (7.34gn Accuracy Plus) to the heaviest (13.47gn JSB Exact Monster), I expected the pellets to lose velocity at a slower rate and retain a greater percentage of their original muzzle energy at range.

    I expected velocity variation to increase with range and for lighter pellets to suffer from more velocity spread at range. I expected ballistic coefficient to increase with pellet mass, and drag coefficient potentially [EDIT] to fall with increasing mass. For all pellets I expected pellet drag to be highest at the muzzle and decrease as range increased.

    Results, Discussion and Half-Arsed Conclusions


    The table below shows the average velocity for each string of five pellets at all ranges, as well as at the muzzle.


    The graph below shows the average velocity of each different pellet as range increases from 0 to 50m:


    From the two sources above, it can be seen that the velocity of all pellets decays at a similar rate. When looking at the data more closely, the two lighter pellets (Falcon and Air Arms) lose less velocity as the range increases, while the rate of velocity loss in the other three pellets either remains reasonably constant (JSB Exact) or increases (JSB Heavy and Monster). This suggests that there is more drag acting on the heavier pellets at longer range, perhaps because of instability.


    The table below shows the average kinetic energy for each string of five pellets at all ranges, as well as at the muzzle.


    The graph below shows the average kinetic energy of each different pellet at ranges from 0 to 50m:


    From both sources we can see that, with the exception of the 13.47gn JSB Monster, the energy of each pellet at the muzzle was proportional to it's mass; the heavier pellets carrying more energy. This is a commonly observed trait in pre-charged rifles. We can see that the lightest pellet (7.33gn Falcon Accuracy Plus) initially loses energy at a faster rate than the other pellets. In keeping with the velocity graph, the heaviest two pellets (10.32gn JSB Heavy and 13.47gn JSB Monster) lost energy at a greater rate than the others as range increased; again suggesting poor drag characteristics.

    The table below shows the average amount of energy retained by each pellet type at each range, as a percentage of their muzzle energy (please discount the spurious "muzzle" column titles on this one - not sure how they got there!):


    The graph below shows the average amount of energy retained by each pellet type at each range, as a percentage of their muzzle energy:


    From the preceding table and graph it can be seen that, while the lightest pellet retains the least energy, the remaining four pellets do not follow the same general trend. Despite being the second lightest in the test, the 7.88gn Air Arms Express retains significantly more energy at 50m (58.5%) than any of the other pellets, regardless of mass.

    This is significant as the lighter Air Arms is traveling faster and so should be subject to a higher drag force. This suggests that the Air Arms Express has a very low drag shape. The results also suggest that the two heavier pellets create significantly more drag than the others; contrary to initial expectations.

    Pellet Velocity and Energy Variation

    The table below shows the extreme velocity spread over each five-shot string at each range:


    From the table above it can be seen that pellet velocity spread at the muzzle is minimal; ranging from 1 to 11ft/s, depending on pellet. It can also be seen that extreme velocity spread increases significantly at range; with the extreme spread at 50m being as much as 52ft/s (Falcon Accuracy Plus). Note that the JSB Monster was not tested completely at 50M, due to significant accuracy problems. In addition many of these heavy pellets could be observed through the 'scope "corkscrewing" as they made their way towards the 50m chrono - suggesting that they were extremely unstable at this range.

    Note that from 20m onwards the Air Arms Express showed very low extreme velocity spread figures; significantly lower than all other pellets at equivalent range - suggesting that it is extremely stable in flight.

    The graph below shows the extreme spread in pellet kinetic energy at range, as a percentage of the average energy at that range:


    From the table above it can be seen that the 13.47gn JSB Monsters have the highest extreme energy spread over all the ranges at which they were tested. We can also see that energy spread for all pellets (except the 7.88gn Air Arms Express) rises almost exponentially with range. From around 15m the Air Arms Express once again show a significantly lower percentage energy spread than all other pellets.

    Time of Flight

    The graph below shows the average time of flight for each pellet at each range:


    From the graph above it can be seen that flight time varies in proportion to pellet mass; the heavier pellets taking longer to reach their target. No surprise there, then :p

    Drag Coefficient (Cd)

    This is where it gets interesting! For those who are unfamiliar with the concept, a shape's drag coefficient is a unit-less number that represents the amount of drag generated by the shape as it moves through the air. Broadly speaking (and transonic/supersonic flow situations excluded), drag coefficient should be reasonably constant regardless of scale or velocity. Cd is a measure of how "aerodynamic" a shape is; the lower the number the lower drag.

    The table below shows the drag coefficient of each pellet with range (as measured with respect to the velocity lost from that at the preceding range), as well as low, high and average values:


    From the table above it can be seen that on average the 7.88gn Air Arms Express shows by far the lowest drag coefficient, and the 13.47gn JSB Exact Monster shows the highest.

    The graph below shows the drag coefficient of each pellet at each range:


    There are several interesting trends to be spotted in the graph above. It can be seen that the heaviest pellet (13.47gn JSB Exact Monster) has by far the highest drag coefficient at all ranges, while the second-lightest pellet (7.88gn Air Arms Express) has the lowest Cd from 15m onwards.

    The two lightest pellets (Falcon Accuracy Plus and Air Arms Express) show a drag coefficient that initially begins to decline at 5-10m before approximately levelling out; showing a general downward trend as range increases. Conversely the two heaviest pellets (JSB Exact Heavy and JSB Exact Monster) show a small initial decline in Cd, which quickly increases with range. The behaviour of the middle pellet (JSB Exact) lies somewhere between these two extremes.

    It is surprising and unexpected that the drag coefficients behave in this way; rather than decreasing with range and giving similar values for all pellet masses (or even lower figures for the heavier pellets). It is suspected that this behavior is because of insufficient stability in flight of the two heavier pellets; the middleweight being borderline and the two lightest being adequately stable.

    Ballistic Coefficient

    The ballistic coefficient (bc) is measure of how well a projectile retains it's energy at range; conversely to a projectile's drag coefficient, the bc takes into account the pellet's size and mass. Larger numbers mean better energy retention at range.

    The table below shows the ballistic coefficient for each pellet at each range (as measured with respect to the velocity lost from that at the preceding range):


    From the table above it can be seen that despite it's low mass, the 7.88gn Air Arms Express has the same mean ballistic coefficient (0.0233) as the much heavier 13.47gn JSB Exact Monster - a figure that is significantly higher than the other pellets on test. This is extremely significant since bc is usually heavily influenced by a pellet's mass - so two pellets of largely different mass suggest that the lighter pellet is producing significantly less drag than expected, the heavy pellet is producing more drag, or a combination of the two.

    Overall Conclusion

    Congratulations to those of you who made it this far :p


    This test has been an eye-opener to me. I fully expected the heavier pellets to perform significantly better at range than the lighter alternatives; retaining more energy, showing less extreme velocity and energy spread, potentially showing a lower drag coefficient and a much higher ballistic coefficient. Evidently, this was not the case. What the testing showed was that ultimately, one of the lightest pellets spanked all of the heavier ones; the performance of which seemed to get worse as their mass increased.

    Explanation of Pellet Behaviour

    So, why are the pellets behaving like this? Admittedly the data is a lot to take in in one hit and I've had over a week to digest it now so it seems a little more clear.

    I strongly suspect that the inferior performance of the heavier pellets is due to a lack of stability causing a variation between the pellet's orientation and the direction in which it's travelling. Basically, it's wobbling in flight, or more correctly experiencing excessive yaw which is responsible for the higher levels of drag at range and wholly unimpressive performance. This excessive yaw grows ever larger as range increases; manifesting itself through exponentially increasing drag, velocity and energy spread as well as rapidly decaying accuracy.

    The next question is inevitably, "why are the heavier pellets more severely affected?" I believe it's down to the highly contentious (in airgun circles) subject of rifling twist rate. It's widely accepted in the world of firearms that, to adequately gyroscopically stabilise a bullet in flight, it must be spun at an appropriate rotational speed. The rotational speed of the bullet is a direct function of it's velocity and rifling twist rate, and the rotational speed required depends on the length, mass and calibre of the projectile - longer bullets requiring more spin to stabilise adequately.

    When a projectile leaves the barrel it usually experiences an amount of yaw; with the nose of the pellet describing tiny circles about the axis of it's direction of travel (known as Nutation). If the pellet is sufficiently gyroscopically stabilised, the forces generated by the rotational motion causes the size of these circles to decrease - damping them out until a zero-yaw (or near) condition is reached and the pellet is flying truly straight.

    Since a projectile will generate more drag when there is some yaw present, the drag coefficient can be used as an indicator for stability - a lower cd representing greater stability. The process of the nutation being damped in the two lightest pellets can be seen in the drag coefficient graph - the cd decreases with range as the yaw is reduced, before effectively levelling out. Conversely for the two heaviest pellets there appears to be a small degree of damping at close range, before the pellets begin to rapidly lose stability and cd grows significantly.

    Ultimately this test suggests to me that, for these pellets fired at the velocities they were from the NJR barrel (IIRC Walther, 1 turn in 18" rifling twist), only the lightest two (7.34gn Falcon Accuracy Plus and 7.88gn Air Arms Express) have a sufficient amount of rotational speed (angular velocity) to give an adequate level of gyroscopic stability. It appears that the 8.44gn JSB Exacts are borderline stable, while the heaviest pellets (10.32gn JSB Exact Heavy and 13.47gn JSB Exact Monster) are clearly insufficiently stabilised.

    There are two ways of increasing the angular velocity (and hence stability) of the heavier pellets - increase the barrel's rifling twist rate, or drive the pellets faster. The latter is not an option on account of our legal energy limit, while the former requires a barrel maker to dare something different to the traditional "set in stone" airgun twist rates of 1:16" to 1:18" twist rates.

    I think this theory is backed up to some extent by the comparison of bc values for the pellets - my bc values for the three lighter (and more stable) pellets are within 5% of most published figures, while the value of .022 for the JSB Heavy is significantly down on the more common value of 0.30 found for this pellet on the 'net - having investigated further, the source of many of the higher figures come from America and Europe; where these pellets are being launched at much higher velocities (850-950ft/s). Their ability to stabalise at these higher velocities adds weight to the idea that they are not being spun fast enough by the rifling at UK-legal velocities.

    What Have I learned?

    I've always used medium to heavy pellets in my PCPs, because they give better internal ballistics in a PCP (higher efficiency, more shots per charge) and I'd always believed that the heavier variants would retain more energy at range, be less susceptible to wind and as a result be more accurate.

    I've never bothered using anything lighter than 8.44gn because of the above facts and assumptions, although I've often heard (and dismissed) a lot of positive anecdotal evidence about the 7.88gn JSB variants in PCPs.

    In the short term I'll definitely be switching to 7.88gn AA Express pellets through my PCPs, while in the long term I'd like to investigate higher twist rate barrels in an effort to exploit the potential benefits that a properly stabilised, heavy pellet could bring in terms of wind resistance and accuracy at range.

    Thanks for reading - I'd be interested to hear any ideas you might have on the subject ;)

    EDIT: Massive thanks are once again due to @PhatMan for spending a fair chunk of his time rescuing the tables from thread-killing-massive-string-of-HTML hell following the forum migration. Cheers Russ! :)
    Last edited: Dec 8, 2019
  2. Awesime

    Awesime Air Arms Xti50 Test Pilot

    Likes Received:
    Oaktree FTC or Skewen!
    We tested Exacts at 50m.

    We found different batches of die 46 exacts gave different readings. One batch went through the chrono at an average of 600 fps, the other was 560 fps.
    The 600fps batch had the smallest fps spread, it was only a few fps, but most importantly both batches grouped the same.

    As a top Ft shooter, accuracy is the end result wanted.
    plinker20 and Precision Hunter like this.
  3. jambo1984

    jambo1984 Engaging Member

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    Dudley West Midlands
    mate that was a good read .....I can see you have put some time into it very good job
    Marky-Boy likes this.
  4. mattyts

    mattyts Donator

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    Some nice reading there Clover...and some effort you put into that too,lots of valuable data :up:
    Marky-Boy likes this.
  5. Stevie Darling

    Stevie Darling Sexual tyrannosaurus

    Likes Received:
    St. Andrews, Jockland.
    Cracking read mate!!!

    Jsb exact express 14.4 push more power in my ultra compared to the heavys, get more shots per charge, and more consistent over the chrono!

    Always an interesting read:up:
    Marky-Boy likes this.
  6. Lydford

    Lydford Posting Addict

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    An excellent pelletology thesis! Your cap and gown are waiting sir ...
    Marky-Boy, pjgtech and foxtrott like this.
  7. Geordie

    Geordie Donator

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    Newcastle Upon Tyne
    Even by your standards this is an epic!:eek::eek::eek:

    I read the first quarter and realised I need a fresh, clear mind, to take it all in and digest.:rolleyes::p Looks a goodun though!:up::up::up::D
    foxtrott likes this.
  8. JD

    JD Donator

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    Thats epic Cloverleaf,

    Do you write for the airgun mags ?

    Still can't get my head around BC's though ?
  9. The Shooter

    The Shooter Member

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    I need to read that again...great work...
  10. jesim1

    jesim1 Kit bitch to the Stars

    Likes Received:
    Wigan/St Helens
    Well done for putting in a hell of a lot of effort and challenging your pre conceived ideas - which to be honest, I read and agreed with!

    Isn't it interesting that Daystate have made a 7.9gn specifically for their PCP orientated rifles?, it almost makes you think they put some serious effort into this kind of stuff?

    Pete2 likes this.
  11. smudgerii

    smudgerii Busy Member

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    Newton le willows
    So I was using the right pellets all the time... What shocks me is I understood it ;)
  12. Snipertez

    Snipertez Donator

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    Devon near Exeter
    Very interesting indeed and good effort Cloverleaf :) many thanks ;)
  13. jjones

    jjones Well-Known Member

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    fantastically well written and extremely interesting, thanks
  14. mattw975

    mattw975 Big Poster

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    I left my heart in Newbury
    Nice NJR mate :)
  15. Shooter22

    Shooter22 Donator

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    Excellent write up, thanks for taking the time to compile such an informative in-depth report.:up:
    I have always believed that mid weight to light/mid weight pellets perform the best in legal limit airguns.

  16. terry1001

    terry1001 Major Poster

    Likes Received:
    Thanks for putting in so much time and effort into this exercise, it's much appreciated. :up:
    Looks like you need an apprentice to help with all the field work.
  17. mrtho

    mrtho Busy Member

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    OMG! It's what I always thought,12ftlbs is totally gutless! :D

    Actually,what a thorough and brilliant piece of research, of benefit to all of us.

    Many thanks!
  18. tombillings916

    tombillings916 Donator

    Likes Received:
    Grimsby - N.E.Lincs.
    Very well written and presented, wish I could have the patience and dedication to submit a test on this level and make it readable and more importantly understandable - pellet ballistics has always been a bit of a 'Black Art' to me and something I could never get my head round but thanks to your in depth test I feel that I now have a much better understanding of what occurs when a pellet leaves the barrel - superb piece of work, well done.
  19. kev02

    kev02 Well-Known Member

    Likes Received:
    Bishop Auckland
    Hi there that is realky good read, you have definitely done yr homework and spent some time with this subject. Well done,
    Atb kev02 :claping:
  20. trumpetier

    trumpetier Pro Poster

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    Just to ecohe everyone else......well done cloverleaf, EXCELLENT informative and well written piece :)

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