I have understood that for airgun pellets you should use GA as the drag coefficient. How much of a difference will using G1 make. Presumably JSB knows what they are doing.
If you want just the data you should click the print button top right which will present the photos as links and strip the pagination. You can then print same to PDF.
That is a GREAT chart .... also telling what was discovered years ago with my exclusive shooting of .20 cal in FT. That being the default in chairgun for the 13.7 JSB was WAY TOO LOW having found the BC was indeed in the .040 to .044 range.
JSB Data from their own test tunnel using a G1 drag coefficient.
Very interesting chart. I'd love to know more about it. The implication is that it came from JSB itself and testing that occurred at the JSB testing tunnel. Did they state this somewhere or do you know an inside man?
Not necessarily questioning the info therein, just wanting to know how reliable of a source it comes from.
The Chrono Connect link is also a big question mark.
That is a GREAT chart .... also telling what was discovered years ago with my exclusive shooting of .20 cal in FT. That being the default in chairgun for the 13.7 JSB was WAY TOO LOW having found the BC was indeed in the .040 to .044 range.
Great info ... printed it out !
Scott S
Scott, the very same portions of the chart were of interest to myself, for the very same reasons you state.
I've mostly campaigned with JSB 10.34s going 920fps (right under 20fpe) with success at my clubs monthly FT matches.
I started down the Raptor .20 road just to explore the .20, both at field target levels at and higher power, specifically to see if there were any BC gains to be had. I shot the Raptor a time or two at matches, the best it did was a 50/52 shooting through a course unofficially after the official match. Not one shot needed to be held outside of the kz, in a windy day that DID require hold-offs when I shot through with the .177.
As for the chart above, after conversions to more familiar numbers, (for the .177, 0.67gram @240m/s to 10.34grains at 787fps and for the .20, 0.89grams at 280m/s to 13.73grains at 918fps) it's not quite an apples to apples comparison. The .177, 10.34s are doing 14.22fpe (for a stated BC of 0.029) while the .20, 13.73s are doing 25.7fpe (for a stated BC of 0.04).
I've measured the 10.34gr .177 as having a BC of 0.0354 when going 925fps. I suspect the BC between the .177 10.34 and the .20 13.73 is closer than the graph suggests, if both projectiles are doing just a bit under 20fpe.
Anyway, I've got that Veteran .20 now and plan to do some testing and even shooting it at some matches to see how it compares.
I DO agree with you, at least from my anecdotal evidence, that there are some gains in BC to be had with the .20 over the .177, in the sub 20FPE field target realm.
As for why they used the G1 model (versus the GA model as everyone seems to accept as the best drag model for diabolo pellets).......your guess is as good as mine. BUUUUT, being JSB, surely they know a little something that the rest of us don't.
This all goes back to the little discussion we had on AGN a few weeks ago. NONE of the BC modeling is a perfect representation of what the pellet is doing in real life. Example from JSBs chart above: they are reporting a BC of 0.047 in the controversial .20 (with 15.89gr). That is a better BC than a bunch of the .25s and .30s and dang close to what they're reporting for the .22 25.4gr Monster RD that lately seems to be the pellet of choice for long range benchrest competitions.
The G1 drag law is not a suitable reference drag law for pellets, never has been and never will be. To use it as a reference for wadcutters or polymag shapes is quite frankly ridiculous. The use of such a reference drag law by JSB is worrying in regard to the depth of their ballistic knowledge. The Ga drag law is better for dome pellets but even this has question marks at higher speeds where the drag increase appears to be underpredicted. The use of reference drag laws of the wrong shape is what causes multiple BCs to be needed at different speeds, if the correct reference drag law is used a single BC value is all that is required. I am not the only person to have questioned the use of G1 in this table.
The effects of using the wrong drag laws in trajectory models will depend on the range and velocity being used. The longer the range and the higher the speed the less likely you are to get an accurate prediction.
I love it when Miles jumps in and provides his professional input.
Are we really trying to say here that JSB (yeah, THAT JSB, the one that makes the undeniably BESt pellets, bar-none, argument/discussion/analysis unecessary) is clueless in this regard?
I don't study ballistics for a living, but I have found in my personal shooting that certain pellets from certain barrels are much more resistant to being deflected by the wind than their measured BC suggests they should be. This has been true across all the calibers that I play with, in my own and in friends guns. Something isn't quite right with that, and the drag laws appear to be the big question mark when considering the factors at play. (fps and wind and pellet weight are what they are, drag laws are the non-defined factor).
Not trying to argue G1 vs GA here at all. Just trying to open up the discussion that we really need a better understanding of what is happening to allow a specific barrel/pellet combo at a specific power level with a lower measured BC to resist wind deflection better than a different barrel/pellet combo with a higher measured BC.
The clearest context for all of the above actually provides a pretty good baseline of parameters for a scientific comparison. In field target most of the competitors are right up under that 20fpe limit. I'd hazard a guess that 90% of the people in my club are shooting between 18.5 and 20fpe. 99% of the time, .177 pellets are being used, and usually the 10.34 or 13.43gr. I have a gun that routinely needs half (and often less) as much hold off on the long shots in the same winds as my competitors. I have measured the BC to be 0.035 from my gun and some of the 13.43gr shooters are measuring better BCs. WHY and HOW?
I shoot .20's at 13.6 wt @ 800 FPS My measured BC is also higher than where Chairgun says yet with JSB's chart the BC is near dead on for the speed being shot. HUH ?
I love it when Miles jumps in and provides his professional input.
Are we really trying to say here that JSB (yeah, THAT JSB, the one that makes the undeniably BESt pellets, bar-none, argument/discussion/analysis unecessary) is clueless in this regard?
I don't study ballistics for a living, but I have found in my personal shooting that certain pellets from certain barrels are much more resistant to being deflected by the wind than their measured BC suggests they should be. This has been true across all the calibers that I play with, in my own and in friends guns. Something isn't quite right with that, and the drag laws appear to be the big question mark when considering the factors at play. (fps and wind and pellet weight are what they are, drag laws are the non-defined factor).
Not trying to argue G1 vs GA here at all. Just trying to open up the discussion that we really need a better understanding of what is happening to allow a specific barrel/pellet combo at a specific power level with a lower measured BC to resist wind deflection better than a different barrel/pellet combo with a higher measured BC.
The clearest context for all of the above actually provides a pretty good baseline of parameters for a scientific comparison. In field target most of the competitors are right up under that 20fpe limit. I'd hazard a guess that 90% of the people in my club are shooting between 18.5 and 20fpe. 99% of the time, .177 pellets are being used, and usually the 10.34 or 13.43gr. I have a gun that routinely needs half (and often less) as much hold off on the long shots in the same winds as my competitors. I have measured the BC to be 0.035 from my gun and some of the 13.43gr shooters are measuring better BCs. WHY and HOW?
It is part of the problem with using BCs to predict performance for pellets, bullets shells, anything. Two projectiles can have the same BC but different crosswind performance due to the shape of their drag curves compared to the reference drag curve and their velocities compared to the velocity at which the BC was measured. With shells the problems became so great, with a large number of BC values being needed for the different velocities in a single trajectory, that the use of purpose drag laws came into use 60 years ago. Bullets are just beginning to use the same methods as the "latest" innovation for long range trajectory prediction. Pellets and slugs may have to follow suite depending on range and the level of detail wanted. The wide variety in shapes of pellets and slugs also goes against being able to use one or two reference drag laws for everything.
The use of BC for wind effect comparison is only a very rough guide, muzzle velocity comes into it as well. The main factor is the difference in time between the actual trajectory and the time for a trajectory in a vacuum. If you measure the time of flight to the target then you should be able to get a good guide to crosswind response.
As for JSB I do not know who they use for their testing or external ballistics. However, based on my observations of and interactions with small arms manufacturers, the levels of knowledge appear to leave something to be desired. I have seen and heard many things which are simply not true being said, tests being carried out without due control of significant variables or using unsuitable instrumentation and unsound conclusions being drawn. Much of it seemed to stem from small arms manufacturers or divisions working on their own in isolation from what was going on elsewhere, hence purpose drag laws being the latest thing just 60 years out of date.
I knew someone working for a major defence manufacturer who was knowledgeable in exterior ballistics (I had trained him myself in some areas) and I asked him one day if his company's small arms division ever asked him to help them as some of their new products looked a little dubious to me. His reply was that they had never asked him for any help or advice. It showed.
Thank you, Miles, for that deep background info. ????
?So, here we airgunner are, hoping and dreaming that those manufacturers making our AG stuff will start making barrels that like slugs....
And scopes with min. parallax to 10y. With turrets and reticle speaking the same lanuage.
And bullpups that don't waste space with needlessly extended bloat stocks, and stingy airtubes shorter than the barrel.
?And then we find out — they don't even consult with the pro's about issues as crucial for AG as drag/BC....! [Miles, another member here said similar things about another pellet manufacturer. ?]
But hey, considering how good airgunning already is — ▪with realatively inexpensive scopes with great glass and features,
▪with slugs at almost-pellet prices (NSA for 5 cents/shot),
▪with good $50 PCP airpumps,
▪with guns bigger, better & more bowerful than ever (again without having to pay premium prices),
▪and the forums and YouTube teaching us how to fix them,....
➔ So I think I stop complaining and start counting my blessings...! ?