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Some half-arsed (.22) velocity decay testing and results

Discussion in 'Anything Airgun Related' started by cloverleaf, Jan 18, 2014.

  1. cloverleaf

    cloverleaf Super Moderator Staff Member Mod/Admin

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    The latest area of the sport to pique my interest has been exterior ballistics. On account of this I've been amassing the gear to test the velocity of projectiles both at the muzzle and down range; in an effort to record their behavior and understand the factors that influence pellet velocity / energy loss at range.

    I plan to do a big test of .177 pellets over 50yds when I get the chance. I recently purchased an F1 Chrony, and yesterday made a Polycarbonate guard for the front; to prevent any errant shots causing catastrophic and expensive damage to the unit.

    Today I took the opportunity to test the setup in the garden. In the interests of continuity and further interest I used the same rifle, pellets and range that the clay terminal ballistic tests were carried out with last year - hoping that the velocity results might add some relevant information to the previous tests.


    Method

    The F1 Chrony was set up at approximately 14yds, in front of a suitable backstop. The rifle (an AA S410k in .22 and fitted with a Combro chrono) was used to fire one series of five pellets of each of the following types: Air Arms Field (15.9gn), Air Arms Hunter (15.9gn), RWS Hobby (11.9gn) and RWS Super H-Point (14.2gn). The velocity of each pellet (both at the muzzle and at the target) was recorded, to the nearest ft/s.

    Following this test, 10 shots with the AA Hunter were fired through the Combro and F1 with the chronoscopes situated as close as possible to each other - realistically the last sensor of the Combro being around 30mm from the first sensor on the F1. The discrepancy in velocity between the two was used to generate a correction/calibration factor for the Combro velocity readings.


    Results

    Firstly the results from the calibration of the two chronoscopes. Below are the velocity results (ft/s) from the 10-shot string over both units, with the average velocity in the final row:

    [TABLE="width: 200"]
    [TR]
    [TD="align: center"]Combro
    [/TD]
    [TD="align: center"]F1 Chrony
    [/TD]
    [/TR]
    [TR]
    [TD="align: center"]560[/TD]
    [TD="align: center"]560[/TD]
    [/TR]
    [TR]
    [TD="align: center"]561[/TD]
    [TD="align: center"]563[/TD]
    [/TR]
    [TR]
    [TD="align: center"]562[/TD]
    [TD="align: center"]567[/TD]
    [/TR]
    [TR]
    [TD="align: center"]561[/TD]
    [TD="align: center"]566[/TD]
    [/TR]
    [TR]
    [TD="align: center"]560[/TD]
    [TD="align: center"]562[/TD]
    [/TR]
    [TR]
    [TD="align: center"]560[/TD]
    [TD="align: center"]561[/TD]
    [/TR]
    [TR]
    [TD="align: center"]554[/TD]
    [TD="align: center"]560[/TD]
    [/TR]
    [TR]
    [TD="align: center"]560[/TD]
    [TD="align: center"]564[/TD]
    [/TR]
    [TR]
    [TD="align: center"]556[/TD]
    [TD="align: center"]560[/TD]
    [/TR]
    [TR]
    [TD="align: center"]551[/TD]
    [TD="align: center"]557[/TD]
    [/TR]
    [TR]
    [TD="align: center"]558.5
    [/TD]
    [TD="align: center"]562.0
    [/TD]
    [/TR]
    [/TABLE]

    Based on the average velocities, a correction factor of +0.6% was applied to all the Combro readings to bring them closer to those recorded by the F1 unit.

    The table below gives the average values (from each 5-shot string) for each pellet at 0 and 14yds, as well as various other bits of information relating to their performance.


    [TABLE="width: 700"]
    [TR]
    [TD="align: center"][/TD]
    [TD="align: center"] Range, yds
    [/TD]
    [TD="align: center"] AA Field
    [/TD]
    [TD="align: center"] AA Hunter
    [/TD]
    [TD="align: center"] RWS Hobby
    [/TD]
    [TD="align: center"] RWS H-Point
    [/TD]
    [/TR]
    [TR]
    [TD]Vel, ft/s
    [/TD]
    [TD="align: center"]0[/TD]
    [TD="align: center"]565.3[/TD]
    [TD="align: center"]563.7[/TD]
    [TD="align: center"]625.1[/TD]
    [TD="align: center"]584.8[/TD]
    [/TR]
    [TR]
    [TD]Vel, ft/s
    [/TD]
    [TD="align: center"]14[/TD]
    [TD="align: center"]538.0[/TD]
    [TD="align: center"]521.2[/TD]
    [TD="align: center"]543.0[/TD]
    [TD="align: center"]522.6[/TD]
    [/TR]
    [TR]
    [TD]Vel. Ex. Spread, ft/s
    [/TD]
    [TD="align: center"]0[/TD]
    [TD="align: center"]6.0[/TD]
    [TD="align: center"]3.0[/TD]
    [TD="align: center"]3.0[/TD]
    [TD="align: center"]5.0[/TD]
    [/TR]
    [TR]
    [TD]Vel. Ex. Spread, ft/s[/TD]
    [TD="align: center"]14[/TD]
    [TD="align: center"]8.0[/TD]
    [TD="align: center"]11.0[/TD]
    [TD="align: center"]20.0[/TD]
    [TD="align: center"]11.0[/TD]
    [/TR]
    [TR]
    [TD]Vel. Loss, ft/s
    [/TD]
    [TD="align: center"]14[/TD]
    [TD="align: center"]27.3[/TD]
    [TD="align: center"]42.5[/TD]
    [TD="align: center"]82.1[/TD]
    [TD="align: center"]62.2[/TD]
    [/TR]
    [TR]
    [TD]Vel. Remaining, %
    [/TD]
    [TD="align: center"]14[/TD]
    [TD="align: center"]95.2[/TD]
    [TD="align: center"]92.5[/TD]
    [TD="align: center"]86.9[/TD]
    [TD="align: center"]89.4[/TD]
    [/TR]
    [TR]
    [TD]Energy, ftlb
    [/TD]
    [TD="align: center"]0[/TD]
    [TD="align: center"]11.29[/TD]
    [TD="align: center"]11.22[/TD]
    [TD="align: center"]10.33[/TD]
    [TD="align: center"]10.79[/TD]
    [/TR]
    [TR]
    [TD]Energy, ftlb[/TD]
    [TD="align: center"]14[/TD]
    [TD="align: center"]10.22[/TD]
    [TD="align: center"]9.59[/TD]
    [TD="align: center"]7.79[/TD]
    [TD="align: center"]8.61[/TD]
    [/TR]
    [TR]
    [TD]Energy Loss, ftlb
    [/TD]
    [TD="align: center"]14[/TD]
    [TD="align: center"]1.06[/TD]
    [TD="align: center"]1.63[/TD]
    [TD="align: center"]2.53[/TD]
    [TD="align: center"]2.17[/TD]
    [/TR]
    [TR]
    [TD]Energy Remaining, %
    [/TD]
    [TD="align: center"]14[/TD]
    [TD="align: center"]90.6[/TD]
    [TD="align: center"]85.5[/TD]
    [TD="align: center"]75.5[/TD]
    [TD="align: center"]79.8[/TD]
    [/TR]
    [TR]
    [TD]Ballistic Coefficient (BC)
    [/TD]
    [TD="align: center"]-[/TD]
    [TD="align: center"]0.035[/TD]
    [TD="align: center"]0.022[/TD]
    [TD="align: center"]0.012[/TD]
    [TD="align: center"]0.016
    [/TD]
    [/TR]
    [TR]
    [TD]Drag Coefficient (Cd)
    [/TD]
    [TD="align: center"]-
    [/TD]
    [TD="align: center"]0.26
    [/TD]
    [TD="align: center"]0.41
    [/TD]
    [TD="align: center"]0.55
    [/TD]
    [TD="align: center"]0.53
    [/TD]
    [/TR]
    [/TABLE]


    Observations

    There's a lot of information in the table above, so I'll try and summarise it as selectively, relevantly and concisely as possible :)

    - At the muzzle, the AA Field produced the most energy (11.29ftlb) followed by the AA Hunter (11.22ftlb), RWS Super H-Point (10.79ftlb) and RWS Hobby (10.33ftlb).

    - At the target, the AA Field retained the most energy (10.22ftlb / 90.6%) followed by the AA Hunter (9.59ftlb / 85.5%), RWS Super H-Point (8.61ftlb / 79.8%) and RWS Hobby (7.79ftlb / 75.5%).

    - At the muzzle, the AA Hunter and RWS Hobby gave the most consistent velocity spread (3ft/s) followed by the RWS Super H-Point (5ft/s) and AA Field (6ft/s).

    - At the target, the AA Field gave the most consistent velocity spread (8ft/s) followed by the AA Hunter and RWS H-point (11ft/s) and RWS Hobby (20ft/s).

    - The AA Field gave the highest ballistic coefficient (0.035) followed by the AA Hunter (0.022), RWS H-Point (0.016) and RWS Hobby (0.012).

    - The AA Field gave the lowest drag coefficient (0.26) followed by the AA Hunter (0.41), RWS H-Point (0.53) and RWS Hobby (0.55).


    Conclusions

    - The muzzle energy of each pellet varies with pellet mass; corroborating the commonly held belief that pre-charged rifles are more efficient with heavier pellets.

    - The percentage energy retained at the target also varies with pellet mass; however this is far from the only determining factor (this will be discussed later).

    - Velocity spread at the target appears to bear little to no correlation with spread at the muzzle (Hobbies gave the best spread at the muzzle (3ft/s) but the worst at the target (20ft/s) while AA Fields gave the worst spread at the muzzle (6ft/s) and the best at the target (8ft/s). It appears that velocity spread seems to relate far more to how much energy is lost between the muzzle and the target (i.e. the pellet with the least drag gives the best velocity spread at the target).

    - Heavier pellets with lower-drag head shapes (AA Field) retain their energy better and have a better ballistic coefficient than those that are light and have poor drag characteristics (RWS Hobby).

    - Round-nose pellets appear to cause the lowest drag; followed by pointed, hollow and then flat-point designs. It's interesting to note the pronounced difference in drag coefficient and BC between the AA Hunter and Field - the only difference being their head shape.


    Further Discussion and Final Thoughts

    This has been a quick and dirty look at energy retention at range; I'm aware that there are plenty of holes in the post but I hope that some of you will find the information of use / interest.

    A few more things I'd like to mention / discuss:


    Relationship between BC and Velocity Spread at Range

    I was a little surprised by the large velocity spread at range by the higher-drag / lower BC pellets; so it appears that a low BC not only means a pellet sheds energy quickly, but also loses consistency quickly (with associated implications for accuracy). This trend has been loosely reinforced by the accuracy I've seen from these pellets; with those of higher BC generally giving better accuracy at range.


    Ballistic Coefficient

    Ballistic coefficient remains a mysterious and little-understood property; complicated by uneasy comparisons with supersonic projectiles that bear little resemblence to the humble airgun pellet. Thanks to the guidance of some forum members and the ever-helpful Jim Tyler (cheers all ;)) the formula used for calculating BC was: (8000 X Natural Log. (V2/V1)). These figures seem a little high (the internetz says 0.030-0.031 for the AA Field, while this test suggests 0.035); since BC for airgun pellets is usually derived using a range of formula it's foolish to compare different figures from different sources; although the numbers in this test should give a fair idea of how the pellets performed with respect to each other.


    Chronoscope Calibration and Error

    On average the Combro Chrony read around 0.6% (3.5ft/s with the test pellet) lower than the F1 (and this was accounted for in the results) however the actual variation ranged from around 0-1% on a shot by shot basis. In addition, despite attempting to test both units "at the muzzle" in reality both items cannot occupy the same space; with the midpoint of the Combro maybe 40-50mm from the muzzle, while the midpoint of the F1 was more like 200-300mm from the muzzle. Given that the test pellet was losing on average nearly 1ft/s per foot, it's possible that the correction factor derived from the test at the muzzle was somewhat low. This possibility is backed up to an extent by the slightly high BC figures.

    Anyway, I hope some of you find this of interest :)
     
    Last edited: Jan 19, 2014
  2. terry1001

    terry1001 Major Poster

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    Very interesting, as usual. Did you consider weighing the pellets to reduce some of the variables? When you do your next testing have you thought about shooting for groups while checking the performance? It might show the effect that the pellet performance has on point of impact and group size although obviously for just one rifle.
     
  3. cloverleaf

    cloverleaf Super Moderator Staff Member Mod/Admin

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    Thanks!

    Tbh this test was just a quickie to run through the procedure and check everything (the range wasn't measured particularly well, amongst other sloppyness), so I doubt that weighing would have helped much in this case. I hadn't previously considered it, but will definitely give weighing and sorting some thought for the "proper" tests - as you say it should reduce some variance :)

    Shooting groups through the chrono will no doubt come with time; however at the moment I'm more interested in testing velocity loss in isolation. I'm planning on testing 5 different pellets over several different ranges - so that should keep me busy enough :p
     
  4. terry1001

    terry1001 Major Poster

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    Looking forward to the next tests, as soon as you get 5 minutes to spare :D
     
  5. Akita177

    Akita177 The Absolute State of Britian podcast

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    Id love to see JSB Heavy,Exact and falcon Acc+ all 3 coming out the barrel close to the legal limit speeds and then at 50yards.
     
  6. timmytree

    timmytree Pro Poster

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    I find it interesting that the AA Hunter pellets came out so well, coupled with the tests on clay it seems they would be well worth a try for hunters.
    AA fields doing so well overall is no surprise to me, I rate them very highly. It would be nice to see a comparison with JSB Exacts.
    Regards
    Tim
     
  7. cloverleaf

    cloverleaf Super Moderator Staff Member Mod/Admin

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    Thanks - 5 minutes / hours / days - what's the difference? :p


    That's pretty much what I'm planning; although they'll all be fired from the same (pre-charged) rifle, so unfortunately won't all be leaving the muzzle at the same energy. I did consider using a selection of rifles to launch the pellets at around the same energy, but this brings in more variables than it removes.

    I could wind up the energy of the test rifle to push the lighter pellets faster, but tbh I think I'll have enough work with the test as it stands. Hopefully if the results are good enough they can be extrapolated to represent the lighter pellets at 12ftlb :)


    I agree. Tbh the Hunters are literally the only dedicated "hunting" pellet (pointed / hollow point) I've ever found to be anything other than utterly useless - over this short range there's nothing (accuracy wise) between them and the field. Over more realistic hunting ranges I'd expect their lower BC to start to harm accuracy and trajectory, though.

    I find it very interesting how there is a very marked difference in performance between the Hunter and Field; which must be wholly due to their different head shapes (since they weigh the same and left the muzzle at nearly the same velocity).

    Anyway, looking forward to getting the "proper" testing done - finger's crossed for next Saturday, but tbh given the variable weather when it will actually get done is anyone's guess..
     
  8. JD

    JD Donator

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    Half-arsed reply

    I like the idea of this thread, but can we see some RWS superdome & H&N Ftt's being included, in .177 .20 & .22 please.

    The airgun mags used to cover this sort of thing, now more interested in how rifle's shoot, rather than what they shoot.


    Yours sinserely

    H.A.R
     
  9. cloverleaf

    cloverleaf Super Moderator Staff Member Mod/Admin

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    I'm certainly not averse to testing a few more pellets in future, however for the time being I'll be concentrating on the five JSB pellets in .177 as this is what interests me most and is a good starting point IMO. Providing it goes well I'll look into expanding the test to include more pellets at a later date :)
     
  10. mark112

    mark112 Engaging Member

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    Hi,

    Firstly thanks once again for an informative thread which appeals to my inner 'geek'. Will the .177 test include the JSB Monster. My rifle chucks out 10.6 grain Bisley Magnums at 11.8 ft.lbs. Just wondering if these Monsters at 13.43 would take it over the limit. I would imagine that quite a few people would have a similar power level setup.

    Thinking about it has anyone done a graph of Pellet Weight against Maximum power from any one given rifle. Presumably with a PCP there must come a point when increasing the pellets mass does not bring about any more power and efficiency must drop off again (similar to the rifles individual power curve but weight as x axis and max power as y axis).

    Mark
     
  11. cloverleaf

    cloverleaf Super Moderator Staff Member Mod/Admin

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    Thanks - glad it's of interest :)

    Firstly, have you tested your rifle with Daystate / JSB Exact Heavies? These seem to be more efficient than the Bis Mags, so you might want to check / adjust it with a few to be on the safe side ;)

    Yes, I intend to test the Monsters, but have already tested them over the chrono at the muzzle and found them to give slightly less energy than the Heavies in my S410k.

    I don't know of an energy v. pellet weight graph, but there's no reason I couldn't knock one up using the data from the coming test!
     
  12. terry1001

    terry1001 Major Poster

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    There's a lot of experimenting that could be done with pellets and their ballistic performance and you could probably spend years at it. I would hazard a guess that pellets with a similar published BC will behave in much the same way down range so cloverleafs choice of some different pellet styles is a good one. The data collected from one rifle won't necessarily transfer to another but once the pellet has left the muzzle it should behave in much the same way no matter which rifle it's fired from. Heavy/light pellets may well not show the same energy/velocity changes in different rifles though.
    It's good news that cloverleaf has the patience and enthusiasm to carry out this work, hats off to him.
     
  13. mark112

    mark112 Engaging Member

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    Hi,

    Not tried JSB Exact Heavies as shop nearest to me/permission does not have them (Knibbs) hence Bismags. Needed something heavy just for setup/legality stakes although may try range testing as they 'look' a decent enough pellet. Must look elsewhere for the JSBs then! (oh for a standard testing pellet!)

    I hadn't seen your previous test of the Monsters as not having a .177 at that time. Slightly relieved that power levels were not higher than Heavies although one did peak a bit higher (maybe a lighter one I hope).

    One thing I was really interested in was the shape of the power curve in your Monster test graph. I notice that the heavier pellets give a more 'loopy' power curve and the Exacts a more flatter curve. Is this normal? The reason I ask is that I have just recorded a full shot string from the S400 (new valve fitted. Pot set to 57mm exactly as you had it) with the Bisleys. I thought the curve was a little arched in profile. That said it did manage to just about get 150 shots from a 190 bar fill (stopped when shots had dropped to same velocity as at start of test .. 75 bar!!) with 80 shots within 11 fps from 155 bar onwards. If a did another shot string using Exacts might I see a flatter curve albeit at a lower power level?

    That said shooting from a bipod at 50 yards has seen good results. First attempt at 50 recorded 10 shots which formed one hole which a 1p coin comfortably covered. 30 yard groupings are virtually always single holers unless I pull a shot. Can't wait to fit a half decent scope on it as currently using an old budget Hawke non-PA one.

    Anyway I digress. Thanks again for posting your findings on this forum.

    Mark
     
  14. Accuspell

    Accuspell Pro Poster

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    Try some 18gn AA fields - they are VERY efficient. I have a feeling they are JSB Heavies in a badged tin. If not, very very close. I know the FAC Rapid users are very fond of them because of their barrel efficiency and flight characteristics. I don't use them myself, just standard JSB Exacts in .20 for me. I have noticed they are as near as the same aiming points/zero as FTT, despite being about 16% heavier (13.7gn v 11.5gn).

    We did some downrange pellet testing in Airgun Shooter a year or so back. Velocities at muzzle, 20 yards and 30 yards. Then ballistic gel impact tests on the terminal effect for wound tracts (for th ebenefit of hunters rather than target shooters). We did a calibre comparison across .177, .20 and .22. Then we did a shape comparison in .22 only - same rifle different SHAPE/weight pellets. Just what is available off the shelf. It was fun and quite interesting. It also disproved some long held beliefs! Like pointed pellets DID NOT HAVE MORE PENETRATION, in fact Verminpell flat heads penetrated much further - due to them losing less velocity over the flight. The rings on the pointies added too much drag in flight, smooth skirt pointies fared little better.

    We have more pellet testing features lined up for the future.
     
  15. cloverleaf

    cloverleaf Super Moderator Staff Member Mod/Admin

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    Yes, I'd highly recommend the JSB/Daystate Heavy as the defacto PCP "test" pellet - IME it's the most consistently efficient pellet through a PCP; so a good bet to ensure that your rifle is legal with anything else the Polis might choose to put through it.

    Regarding the energy curve of the different pellets; I'm afraid that your suggestions are not supported by my experiences - In practice I found that not only did the Heavies give a greater peak muzzle energy, but also gave a higher amount of acceptable shots per charge than the exacts. In terms of the internal ballistics of the rifle, the Heavies win every time.

    Sounds like you're winning with your rifle regardless of what you choose to put through it!


    I agree, the 18gn pellets are very good, and yes, I believe they're also sourced from JSB. Tbh it seems you can't go wrong with any of JSB's offerings :)

    An interesting point about the pellet head shape - pointed pellets certainly do generate more drag; meaning the penetrate less but create larger diameter impact channels. Surprised about the Verminpell's behaviour though - perhaps because it lost less energy through pellet deformation as it uses a harder lead..?
     

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