JSB 22 cal 18.13 gr Ballistic Coefficient
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January 11, 2019 at 9:49 pm Link
Found online ballistic coefficients for JSB 22 cal 18.13 gr as low as 0.027 and up to 0.043. So decided to run an experiment. Using an FX Impact with a muzzle velocity of 870 fps shot at 45 and 93 yards. Used drop distance measured from sight zero and online trajectory calculators to arrive a BC of 0.0288. Plan to do more testing to see how well 0.0288 BC fits trajectory are various other distance.
What BC are you using?
Found online ballistic coefficients for JSB 22 cal 18.13 gr as low as 0.027 and up to 0.043. So decided to run an experiment. Using an FX Impact with a muzzle velocity of 870 fps shot at 45 and 93 yards. Used drop distance measured from sight zero and online trajectory calculators to arrive a BC of 0.0288. Plan to do more testing to see how well 0.0288 BC fits trajectory are various other distance.
What BC are you using?
January 11, 2019 at 9:58 pm LinkHave tried the drop method and get wildly varying numbers. Did that today in fact with Cricket mini and Mutant. One at 855 FPS, the other at 900 FPS. Did BC three times with Cricket and twice with Mutant. 45 and 85 yards. BC varies between .027 and .068. I have no faith in this method. I much prefer using velocity at muzzle and a specified distance. Seems to be much more accurate.
Have tried the drop method and get wildly varying numbers. Did that today in fact with Cricket mini and Mutant. One at 855 FPS, the other at 900 FPS. Did BC three times with Cricket and twice with Mutant. 45 and 85 yards. BC varies between .027 and .068. I have no faith in this method. I much prefer using velocity at muzzle and a specified distance. Seems to be much more accurate.
January 11, 2019 at 10:54 pm LinkI agree with @centercut Mike. You can do it with 1 chronograph it just takes a few more steps. Set up your chrony at the muzzle and take the average of say 10 or 20 shots, then move the chrony to various or the end distance and repeat. BC will vary depending on twist rate & velocity (among other things).
I agree with @centercut Mike. You can do it with 1 chronograph it just takes a few more steps. Set up your chrony at the muzzle and take the average of say 10 or 20 shots, then move the chrony to various or the end distance and repeat. BC will vary depending on twist rate & velocity (among other things).
January 11, 2019 at 10:55 pm LinkOh and if I don't have time to gather my own BC i usually use .033
Oh and if I don't have time to gather my own BC i usually use .033
January 12, 2019 at 5:32 am LinkOn some calculators it has a box to enter twist rate. Anyone know what I should enter for an FX smooth twist barrel. It is a .25 on an mk1 wildcat.
On some calculators it has a box to enter twist rate. Anyone know what I should enter for an FX smooth twist barrel. It is a .25 on an mk1 wildcat.
January 12, 2019 at 8:51 am LinkI use 0.031 at 860fps muzzle velocity and it matches my trajectory almost exactly, for my gun. (It is a little different over/around 90100 yards, but mostly works.)
Tsmith, I heard the smooth twist X is 1 in 30 twist. Not sure if that is the same for the regular ST barrel, but it may help.
I use 0.031 at 860fps muzzle velocity and it matches my trajectory almost exactly, for my gun. (It is a little different over/around 90100 yards, but mostly works.)
Tsmith, I heard the smooth twist X is 1 in 30 twist. Not sure if that is the same for the regular ST barrel, but it may help.
January 12, 2019 at 10:12 am LinkMichael
I agree with @centercut Mike. You can do it with 1 chronograph it just takes a few more steps. Set up your chrony at the muzzle and take the average of say 10 or 20 shots, then move the chrony to various or the end distance and repeat. BC will vary depending on twist rate & velocity (among other things).
Just make sure to put a shield plate in front of the crony , for some odd reason they don't work very well when you punch a hole in them, and good ol Murphy seems too to like to poke his head in when you least expect it
Michael
I agree with @centercut Mike. You can do it with 1 chronograph it just takes a few more steps. Set up your chrony at the muzzle and take the average of say 10 or 20 shots, then move the chrony to various or the end distance and repeat. BC will vary depending on twist rate & velocity (among other things).
Just make sure to put a shield plate in front of the crony , for some odd reason they don't work very well when you punch a hole in them, and good ol Murphy seems too to like to poke his head in when you least expect it
January 12, 2019 at 4:25 pm Linktsmith
On some calculators it has a box to enter twist rate. Anyone know what I should enter for an FX smooth twist barrel. It is a .25 on an mk1 wildcat.
Seldom are things as simple as they seem.
FX smooth twist barrels and FX smooth twist X barrels are very different. Then within these two there are differences depending upon calibre and in the first ST depending upon which of more than 18 iterations made and pellet weight and velocity.
Example: ST in .22 calibre had a nominal actual barrel twist rate of 1:16". But the more interesting "rating" relates to the emerging spin rate of the pellet, which, because the pellet skims through that very short "rifled " section of barrel, can vary widely depending upon the pellet weight, its velocity, and the barrel iteration. Thus, without defining these parameters, when I tested my .22 ST barrel the spin rate averaged 1:64". When Fredrik Axelsson repeated my test he got 1:40+" with a later iteration barrel than mine; and Dan Brown got 1:160" with an earlier iteration.
Then when I tested my .25 cal ST barrel with JSB Kings it produced 1:75" but with a heavier pellet it was 1:90".
However, because all these still shot with great accuracy to very long range because of the flare stabilisation of diabolos, then it is of little consequence.
Enter the FX smooth twist X barrel and we have the pellets emerging at the same spin rate as the barrel twist rates – which Fredrik varies according to accuracy tests done in house. Initially such rates have been established using the most popular JSB pellets within each calibre. My STX .25 barrel is 1:28" nominal and again because of flare stabilisation it shoots all three JSB pellets to sub moa at 100 yd. Barracudas, because of their head and skirt profile are not quite so stability tolerent but still shoot sub moa to 50 yd and further.
I guess I have probably lost most readers' interest by now but the really interesting part is what the changing downrange pellet spin rate interacting with flare stability (or lack), remaining static stability, pellet tractability and the forces of gravity and wind do to dynamic stability.
nvelkhunter – if you enter bc 0.034 as a GA profile into your Chairgun programme, you should find it close to the money in giving you workable trajectory tables at least to 100 yd and probably much further. … best regards from OZ, HarryyrraH.
tsmith
On some calculators it has a box to enter twist rate. Anyone know what I should enter for an FX smooth twist barrel. It is a .25 on an mk1 wildcat.
Seldom are things as simple as they seem.
FX smooth twist barrels and FX smooth twist X barrels are very different. Then within these two there are differences depending upon calibre and in the first ST depending upon which of more than 18 iterations made and pellet weight and velocity.
Example: ST in .22 calibre had a nominal actual barrel twist rate of 1:16". But the more interesting "rating" relates to the emerging spin rate of the pellet, which, because the pellet skims through that very short "rifled " section of barrel, can vary widely depending upon the pellet weight, its velocity, and the barrel iteration. Thus, without defining these parameters, when I tested my .22 ST barrel the spin rate averaged 1:64". When Fredrik Axelsson repeated my test he got 1:40+" with a later iteration barrel than mine; and Dan Brown got 1:160" with an earlier iteration.
Then when I tested my .25 cal ST barrel with JSB Kings it produced 1:75" but with a heavier pellet it was 1:90".
However, because all these still shot with great accuracy to very long range because of the flare stabilisation of diabolos, then it is of little consequence.
Enter the FX smooth twist X barrel and we have the pellets emerging at the same spin rate as the barrel twist rates  which Fredrik varies according to accuracy tests done in house. Initially such rates have been established using the most popular JSB pellets within each calibre. My STX .25 barrel is 1:28" nominal and again because of flare stabilisation it shoots all three JSB pellets to sub moa at 100 yd. Barracudas, because of their head and skirt profile are not quite so stability tolerent but still shoot sub moa to 50 yd and further.
I guess I have probably lost most readers' interest by now but the really interesting part is what the changing downrange pellet spin rate interacting with flare stability (or lack), remaining static stability, pellet tractability and the forces of gravity and wind do to dynamic stability.
nvelkhunter  if you enter bc 0.034 as a GA profile into your Chairgun programme, you should find it close to the money in giving you workable trajectory tables at least to 100 yd and probably much further. ... best regards from OZ, HarryyrraH.
January 12, 2019 at 6:58 pm LinkGreat post Yarrhthanks for sharing that. Question: how did you ‘measure’ the effective twist rates? I would be interested just to understand how you did that…
I’m assuming that twist rates on rifled or polygon barrels are more closely matched to the barrel’s twist rate as manufacturered?
Thanks for sharing the knowledge with the community!
Sean
Great post Yarrhthanks for sharing that. Question: how did you ‘measure’ the effective twist rates? I would be interested just to understand how you did that...
I’m assuming that twist rates on rifled or polygon barrels are more closely matched to the barrel’s twist rate as manufacturered?
Thanks for sharing the knowledge with the community!
Sean
January 12, 2019 at 11:52 pm LinkSMH77
Great post Yarrhthanks for sharing that. Question: how did you ‘measure’ the effective twist rates? I would be interested just to understand how you did that…
I’m assuming that twist rates on rifled or polygon barrels are more closely matched to the barrel’s twist rate as manufacturered?
Thanks for sharing the knowledge with the community!
Sean
Sean, We can basically assume that for fully rifled barrels, regardless of rifling profile, the initial pellet spin rate is the same as the barrel displays. My measurements relevant to that show within half an inch discrepency, which by assumption can be considered as a reflection of the accuracy of the method percentagewise. Eg., ( 0.5 ÷ 17 ) × 100 %, or say roughly 3% for a 1:17" barrel rifling.
To respond to the first part of your question – pellets with signature marks, such as a careful ink mark on the pellet head from near centre to near expected rifling marks, are shot through three screens separated at precisely measured distances with gaps preferably less than and more than the nominal barrel twist rate.
The screens must be located such that their physical orientation is the same – and is known in regard to vertical and horizontal position. The screens should be thin enough but fine enough to be cleanly perforated by the pellets without upset.
The screens are then examined to see the marks made by the ink. The pellet rotation indicated by the second and third screens, compared to the first, is resolved in degrees.
Then with the known measurements between the screens, a little trig and maths resolves one rotation into a rate per inches of travel as in 1:X".
Of course the right or left twist of the rifling has to be taken into account. Any error will be related to the accuracy of the measurements, but as stated above, my data for full length rifling has been within about 3% of manufacturer's stated value . So an original smooth twist barrel that gave me an average of 1:64" could be say +/ a couple of inches.
I hope that is somewhat clear in concept and helpful in seeing where I was coming from. … Kind regards, Harry.
SMH77
Great post Yarrhthanks for sharing that. Question: how did you ‘measure’ the effective twist rates? I would be interested just to understand how you did that...
I’m assuming that twist rates on rifled or polygon barrels are more closely matched to the barrel’s twist rate as manufacturered?
Thanks for sharing the knowledge with the community!
Sean
Sean, We can basically assume that for fully rifled barrels, regardless of rifling profile, the initial pellet spin rate is the same as the barrel displays. My measurements relevant to that show within half an inch discrepency, which by assumption can be considered as a reflection of the accuracy of the method percentagewise. Eg., ( 0.5 ÷ 17 ) × 100 %, or say roughly 3% for a 1:17" barrel rifling.
To respond to the first part of your question  pellets with signature marks, such as a careful ink mark on the pellet head from near centre to near expected rifling marks, are shot through three screens separated at precisely measured distances with gaps preferably less than and more than the nominal barrel twist rate.
The screens must be located such that their physical orientation is the same  and is known in regard to vertical and horizontal position. The screens should be thin enough but fine enough to be cleanly perforated by the pellets without upset.
The screens are then examined to see the marks made by the ink. The pellet rotation indicated by the second and third screens, compared to the first, is resolved in degrees.
Then with the known measurements between the screens, a little trig and maths resolves one rotation into a rate per inches of travel as in 1:X".
Of course the right or left twist of the rifling has to be taken into account. Any error will be related to the accuracy of the measurements, but as stated above, my data for full length rifling has been within about 3% of manufacturer's stated value . So an original smooth twist barrel that gave me an average of 1:64" could be say +/ a couple of inches.
I hope that is somewhat clear in concept and helpful in seeing where I was coming from. ... Kind regards, Harry.
January 14, 2019 at 4:19 pm LinkInteresting and clever methodthanks Harry! What do you use for screen material (cardboard?)? I'm not sure where to start with twist rate expectations for a LW Polygon barrel, or a RAW .30 cal barrelany ideas?
Sean
Interesting and clever methodthanks Harry! What do you use for screen material (cardboard?)? I'm not sure where to start with twist rate expectations for a LW Polygon barrel, or a RAW .30 cal barrelany ideas?
Sean
January 14, 2019 at 6:04 pm Link0.045 BC at 930 fps matches my actual DOPE from 200 to 238 yards. At 273 yards the BC drops to 0.038.
This is if you believe chairgun of course, and manipulate the BC to match the actual DOPE numbers.
0.045 BC at 930 fps matches my actual DOPE from 200 to 238 yards. At 273 yards the BC drops to 0.038.
This is if you believe chairgun of course, and manipulate the BC to match the actual DOPE numbers.
January 14, 2019 at 8:30 pm LinkSMH77
Interesting and clever methodthanks Harry! What do you use for screen material (cardboard?)? I'm not sure where to start with twist rate expectations for a LW Polygon barrel, or a RAW .30 cal barrelany ideas?
Sean
Sean, very very light cardboard or strong paper – white of course to pick up the ink/biro – stretched tightly and all three screens precisely aligned so that when you are drawing and subtending angles for measurement the pellet rotation to screen 2 and 3 can be assessed from the line of the pellet ink mark on the first screen. Have fun, Harry.
SMH77
Interesting and clever methodthanks Harry! What do you use for screen material (cardboard?)? I'm not sure where to start with twist rate expectations for a LW Polygon barrel, or a RAW .30 cal barrelany ideas?
Sean
Sean, very very light cardboard or strong paper  white of course to pick up the ink/biro  stretched tightly and all three screens precisely aligned so that when you are drawing and subtending angles for measurement the pellet rotation to screen 2 and 3 can be assessed from the line of the pellet ink mark on the first screen. Have fun, Harry.
January 18, 2019 at 5:21 pm LinkJust watched AEAC's review for the 22 cal FX Dreamline. During video, velocity data for each shot was presented. For 50 yard shots, speed at every 10 yards was given and for 100 yard shots every 20. Using ChairGun and making some assumptions, ballistic coefficients were arrived at by iterating BC until the calculated target velocity matched the measured velocity. See attached. Thoughts and comments?
FPS Source AEAC Calculated Source Hawke ChairGun Pro (v4.3.8) Gun FX Dreamline Caliber 22 JSB 18.13 gr Temp 75 Assumed R Humidity 80% Pressure 940 mBar Altitude 100 Feet Wind Speed 0 Wind Angle 90 Target 50 yards 100 yards Shot 1 2 3 4 5 1 2 3 4 5 Ballistic Coef. 0.0350 0.0417 0.0275 Measured Calculated Delta Measured Calculated Delta Measured Calculated Delta Muzzle 870 870 0 866 871 871 0 868 872 876 880 880 0 879 879 872 10 843 838 5 841 845 844 1 842 846 20 816 808 8 815 819 819 0 816 819 826 822 801 21 825 825 820 30 788 782 6 790 794 795 (1) 790 792 40 758 756 2 766 769 773 (4) 766 767 776 761 737 24 769 768 771 50 732 732 0 747 752 752 0 742 739 60 728 699 680 19 708 709 725 70 80 662 642 629 13 648 653 681 90 100 624 583 583 0 583 607 na Just watched AEAC's review for the 22 cal FX Dreamline. During video, velocity data for each shot was presented. For 50 yard shots, speed at every 10 yards was given and for 100 yard shots every 20. Using ChairGun and making some assumptions, ballistic coefficients were arrived at by iterating BC until the calculated target velocity matched the measured velocity. See attached. Thoughts and comments?
FPS Source AEAC https://www.youtube.com/watch?time_continue=304&v=VH5LoEKtol0
Calculated Source Hawke ChairGun Pro (v4.3.8) Gun FX Dreamline Caliber 22 JSB 18.13 gr Temp 75 Assumed R Humidity 80% Pressure 940 mBar Altitude 100 Feet Wind Speed 0 Wind Angle 90 Target 50 yards 100 yards Shot 1 2 3 4 5 1 2 3 4 5 Ballistic Coef. 0.0350 0.0417 0.0275 Measured Calculated Delta Measured Calculated Delta Measured Calculated Delta Muzzle 870 870 0 866 871 871 0 868 872 876 880 880 0 879 879 872 10 843 838 5 841 845 844 1 842 846 20 816 808 8 815 819 819 0 816 819 826 822 801 21 825 825 820 30 788 782 6 790 794 795 (1) 790 792 40 758 756 2 766 769 773 (4) 766 767 776 761 737 24 769 768 771 50 732 732 0 747 752 752 0 742 739 60 728 699 680 19 708 709 725 70 80 662 642 629 13 648 653 681 90 100 624 583 583 0 583 607 na January 20, 2019 at 9:58 pm LinkBased on continued analysis using ChairGun, it appears that the G8 profile best fits the 100 yard velocity data taken at 40, 60 and 100 yards.
M #2 = Measured data from second shot
M #3 = from third shot
GA calculations are with BC = 0.0222
G8, BC = 0.0283
Velocity M #2 M #3 GA G8
Muzzle 880 879 880 880 40 yrds 761 769 708 746 60 yrds 699 708 643 687
100 yrds 583 583 583 583 Based on continued analysis using ChairGun, it appears that the G8 profile best fits the 100 yard velocity data taken at 40, 60 and 100 yards.
M #2 = Measured data from second shot
M #3 = from third shot
GA calculations are with BC = 0.0222
G8, BC = 0.0283
Velocity M #2 M #3 GA G8
Muzzle 880 879 880 880 40 yrds 761 769 708 746 60 yrds 699 708 643 687
100 yrds 583 583 583 583 January 21, 2019 at 6:31 am LinkRh:
Using your M#2 velocity figures 880, 761, 699, 583 fps for 0 yd, 0 to 40 yd, 0 to 60 yd and 0 to 100 yd respectively, and taking account of apparent changes of bc over each of these intervals the Chairgun bc calculator in tools gives me bc's of 0.0349, 0.0321, and 0.0289 respectively @ altitude 100 ft, 75dF, 80%RH (the given data).
Then plugging each of these bc's respectively into the Chairgun GA gives me actual M#2/predicted velocities of 40 yd 761/761.9; 60 yd 699/700.7; 100 yd 583/586 fps.
Those are very close GA predictions.
Two points from this: 1. From studies I did in the past, I know bc changes as pellets progress down range for one or a number of reasons that relate to static and dynamic stability and resulting tractability. My studies indicated that for a pellet settling well, the bc tends to improve with range and time. The GA somewhat takes this into account and highlights the fine print of using a bc appropriate to range and other relevant variables. Example – for this particular rifle and pellets, one could use a bc of 0.0289 as the average over the 100 yd etc.
Point 2. It would appear that for this rifle and pellets, under the conditions of wind, temp, RH, altitude etc., the bc was getting worse as range increased, not better. I would read this as indicating the stability of the pellet was changing for the worse. It would only be conjecture to draw any conclusions as to the reason though. It could be as simple as downrange wind upsetting pellet stability or: some gun pellet interaction which disallowed for good dynamic stability.
I have not computed for shot M#3 – and hope at this late hour midnight here in OZ that I have not made any gross errors, Make of it what you will. Best regards Harry.
Rh:
Using your M#2 velocity figures 880, 761, 699, 583 fps for 0 yd, 0 to 40 yd, 0 to 60 yd and 0 to 100 yd respectively, and taking account of apparent changes of bc over each of these intervals the Chairgun bc calculator in tools gives me bc's of 0.0349, 0.0321, and 0.0289 respectively @ altitude 100 ft, 75dF, 80%RH (the given data).
Then plugging each of these bc's respectively into the Chairgun GA gives me actual M#2/predicted velocities of 40 yd 761/761.9; 60 yd 699/700.7; 100 yd 583/586 fps.
Those are very close GA predictions.
Two points from this: 1. From studies I did in the past, I know bc changes as pellets progress down range for one or a number of reasons that relate to static and dynamic stability and resulting tractability. My studies indicated that for a pellet settling well, the bc tends to improve with range and time. The GA somewhat takes this into account and highlights the fine print of using a bc appropriate to range and other relevant variables. Example  for this particular rifle and pellets, one could use a bc of 0.0289 as the average over the 100 yd etc.
Point 2. It would appear that for this rifle and pellets, under the conditions of wind, temp, RH, altitude etc., the bc was getting worse as range increased, not better. I would read this as indicating the stability of the pellet was changing for the worse. It would only be conjecture to draw any conclusions as to the reason though. It could be as simple as downrange wind upsetting pellet stability or: some gun pellet interaction which disallowed for good dynamic stability.
I have not computed for shot M#3  and hope at this late hour midnight here in OZ that I have not made any gross errors, Make of it what you will. Best regards Harry.

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