GTA
All Springer/NP/PCP Air Gun Discussion General => Air Gun Gate => Topic started by: Pellgunfun on June 03, 2015, 09:10:02 AM
-
Hi,
The only BC numbers I can find for the JSB 15.89gr pellet is 0.031. It's not even listed in Chairgun, and some that I find in Chairgun have to be changed because I haven't really found them to be spot on. Is 0.031 BC for the 15.89 pellet accurate, or is there a more accurate BC I should be using for that pellet. I've been traveling a lot with work so my ability to scour the internet is a bit limited right now, but I can logon and check out the GTA forums. I'd like to get all my data squared away before I get back home, and start doing some testing. If anyone has accurate BC numbers for this pellet, "I'll be a thanking you".
Lol, can anyone name the movie that the above quote is from??? Come on now, It's a great movie and it comes on every year. :)
-
Here's a good post about BC from a little while back. He has the JSB listed as 15.9 once and then 15.7 in the chart, but I think that's the pellet you are looking for.
http://www.gatewaytoairguns.org/GTA/index.php?topic=14735.0 (http://www.gatewaytoairguns.org/GTA/index.php?topic=14735.0)
-
The BC varies depending on velocity because the drag models used don't work well for pellets.... Using the G1 drag model (the most common), for the JSB Exact Jumbo 15.9 gr. it is about 0.032 at 700 fps, increases to 0.042 at 800-850 fps, and then starts dropping again, to about 0.032 at 950 fps, and then it really starts to tank above that.... The best way to find out your drop for your pellets in your gun is to shoot at various ranges and record them....
Bob
-
I'm gonna focus on keeping the muzzle FPS at 900 fps to about 910 fps at the most I think. No sense going beyond that I think.
-
JSB 15.89 Jumbo Exact in my D460: BC measured at 0.0330. The gun is a 24 fpe gun so whatever that works out at. That agrees pretty closely with what Bob said.
-
The BC varies depending on velocity because the drag models used don't work well for pellets....
Bob
I look forward, very much, to seeing your work in this area. If I may help in some way, please let me know. Have Crony will measure data =)
-
I got this number from doing a few things . First from a real life start to finish o to 50 meters crony test . At 0 out of the barrel the crony read 553.5 fps and at 50 meters it read 416.4 . watch this video https://youtu.be/cyTZGOMSMUk . You can see the numbers at each distance . I then took this into chairgun . I entered the pellet weight 15.89 and the nuzzle velocity as 553.5 . I set the end range as 55 yards which is pretty close to 50 meters . I scrolled the table down so I could see the 55 yard fps number .Then I started changing the BC numbers till it matched the 50 meter reading of the crony which is 416.4 The closest I could get was 416.5 thats pretty close and the other numbers from 0 to 50 matched as well . The BC number that made this work was 0.0227 the gun used was a lgv master pro . So I would say 0.0227 would be a real life BC number to use in chairgun .
-
At the velocity you tested at....
HAM finds it to be 0.031 at just over 900 fps using the GA drag model.... https://hardairmagazine.com/ballistic-coefficients/
Bob
-
So it appears that BC as far as air guns go is that every gun with a different fps is going to produce a different BC . 553.5 fps = BC 0.0227. I would like to see what other fps's BC turn out to be . Maybe we can figure out a formula if we start off with a low fps and go to the high fps . Has anyone listed the BC for the same pellet with every fps from lets say 553.5 and up ? Lets not use a model . Lets do a real life test of the pellet . I just did a little chairgun BC number changing from 0.0227 to 0.0310 with a 912 fps gun at 50 yards the drop difference is .3 at 0.0277 the drop was 6.5 and with the 0.0310 the drop was 6.2 . At 100 yards looking through the scope its .8 of a mildot difference or 4 inches . So at longer distances it really makes a difference .
-
Every pellet is different, and there is no formula that can be applied.... Part of the problem is that the "drag model" used to compute the BC (usually either G1 or GA) is not a great match for our pellets (nor could it be, with so many different pellet shapes)…. It is particularly inaccurate in the transonic range, over Mach 0.8 (900 fps)….
The very best way for one pellet in one gun is to set up targets at varying distances and make up a "range card" for your own setup....
Bob
-
So it appears that BC as far as air guns go is that every gun with a different fps is going to produce a different BC . 553.5 fps = BC 0.0227. I would like to see what other fps's BC turn out to be . Maybe we can figure out a formula if we start off with a low fps and go to the high fps . Has anyone listed the BC for the same pellet with every fps from lets say 553.5 and up ? Lets not use a model . Lets do a real life test of the pellet . I just did a little chairgun BC number changing from 0.0227 to 0.0310 with a 912 fps gun at 50 yards the drop difference is .3 at 0.0277 the drop was 6.5 and with the 0.0310 the drop was 6.2 . At 100 yards looking through the scope its .8 of a mildot difference or 4 inches . So at longer distances it really makes a difference .
I think the BC would also be different from different guns at the same fps.
Does the rifle achieve its 800fps from 1,000psi and a long barrel or 3,300 psi and a shorter barrel? Add in port size, valve duration, etc. and I would guess that the way the skirt is blown out would be different.
I think all that matters is 2 things. 1) Is the drop and accuracy acceptable to you with your gun. 2) Is there enough fpe/penetration at the target for your intentions.
-
I am running the pc version of Chairgun and in toolbox it has custom profile and edit custom profile...so you can create a new profile... after you learn the Cd(drag coefficient at a particular velocity... it goes .2-.4-.6-.8-1-1.2 mach and so on... So we can create the drag curve for any pellet not just an overall pellet...
-
Kirby, that is true.... However, you need the Cd for your pellet at the different velocities to create that custom drag profile.... This means a lot of Chrony work at all those different velocities, or using a LabRadar at a few different velocities, and then using that data to calculate the Average Cd for each Mach number that you can input.... When you are said and done, the number of input points are rather limited, so you end up with a crude approximation of what the actual drag curve is....
To make it worse, every pellet will produce a different drag curve.... The only company I know that does this is Lapua, and they have the drag curves, and the software to use them, to accurately predict the downrange velocity, energy and trajectory, but only for their own bullets, of course.... I dream of being able to do that someday, but until I retire in 2021 I sure won't have the time to even start.... At least the articles I am writing for Hard Air Magazine will pay for the LabRadar before then.... ::)
Sam, you are correct, the exact same pellet can have a different BC, even at the same velocity, depending on how much the gun used distorts the skirt....
(http://i378.photobucket.com/albums/oo221/rsterne/Ballistics/Pellet%20Obturation_zpsyzq1fbkq.png) (http://s378.photobucket.com/user/rsterne/media/Ballistics/Pellet%20Obturation_zpsyzq1fbkq.png.html)
Fired pellets on the left, unfired (but pushed through the bore) on the right.... Photo courtesy Lloyd Sikes....
Bob
-
So it appears that BC as far as air guns go is that every gun with a different fps is going to produce a different BC . 553.5 fps = BC 0.0227. I would like to see what other fps's BC turn out to be . Maybe we can figure out a formula if we start off with a low fps and go to the high fps . Has anyone listed the BC for the same pellet with every fps from lets say 553.5 and up ? Lets not use a model . Lets do a real life test of the pellet . I just did a little chairgun BC number changing from 0.0227 to 0.0310 with a 912 fps gun at 50 yards the drop difference is .3 at 0.0277 the drop was 6.5 and with the 0.0310 the drop was 6.2 . At 100 yards looking through the scope its .8 of a mildot difference or 4 inches . So at longer distances it really makes a difference .
I think the BC would also be different from different guns at the same fps.
Does the rifle achieve its 800fps from 1,000psi and a long barrel or 3,300 psi and a shorter barrel? Add in port size, valve duration, etc. and I would guess that the way the skirt is blown out would be different.
I think all that matters is 2 things. 1) Is the drop and accuracy acceptable to you with your gun. 2) Is there enough fpe/penetration at the target for your intentions.
Once the pellet leaves the barrel, it doesn't care how it got the 1000 fps. Other than a few "minor" things like twist rate and exact bore size, the gun shouldn't matter hardly at all.
-
well actually twist rate may not be a "small thing" it may determine when the pellet becomes dynamically unstable... I think the new Maximus barrels are about 1:19 twist rather than 1:16... also the XL 725 barrels seem to be around 1:19 twist also rather than the 1:15 of the .25 Mrod...
I am pretty sure slower twist with most pellets helps long range accuracy and reduces spiraling which will have more than a small effect on B.C.
Bob I think I am the one who told you about Lapua using Doppler.. ;) in 2015 It was back when the 200g .308 Whiteout BBT was being discussed while it was being developed...
and yep it would be a lot of work to get the model for each pellet but it would be about the best "good" B.C. we could come up with... We could them name it GP one thru what ever is needed.. ;)
-
So it appears that BC as far as air guns go is that every gun with a different fps is going to produce a different BC . 553.5 fps = BC 0.0227. I would like to see what other fps's BC turn out to be . Maybe we can figure out a formula if we start off with a low fps and go to the high fps . Has anyone listed the BC for the same pellet with every fps from lets say 553.5 and up ? Lets not use a model . Lets do a real life test of the pellet . I just did a little chairgun BC number changing from 0.0227 to 0.0310 with a 912 fps gun at 50 yards the drop difference is .3 at 0.0277 the drop was 6.5 and with the 0.0310 the drop was 6.2 . At 100 yards looking through the scope its .8 of a mildot difference or 4 inches . So at longer distances it really makes a difference .
I think the BC would also be different from different guns at the same fps.
Does the rifle achieve its 800fps from 1,000psi and a long barrel or 3,300 psi and a shorter barrel? Add in port size, valve duration, etc. and I would guess that the way the skirt is blown out would be different.
I think all that matters is 2 things. 1) Is the drop and accuracy acceptable to you with your gun. 2) Is there enough fpe/penetration at the target for your intentions.
Once the pellet leaves the barrel, it doesn't care how it got the 1000 fps. Other than a few "minor" things like twist rate and exact bore size, the gun shouldn't matter hardly at all.
But before the pellet leaves the barrel, I think it matters. I also wonder if the depth of the rifling effects the BC or If polygonal rifling is used.
Also, what if what we think of as a “minor” thing is actually quite a big deal due to the BC already being so poor?
-
I tend to calculate BC from POI at range.
It can be found in Chair Gun toolbox
-
That works well IF you can accurately determine the center of the group at 2 different ranges.... and the further apart the better....
Bob
-
I was talking about the jsb 15.89 pellet not every pellet made .
If you watch the video I post above . Take the numbers you see in the video for the 15.89 pellet that he list at the different distances for the 553.5 fps and ending at 416.4 at 50 meters they all are the same in the chairgun program . So his real life shooting of the pellet through the crony at the different distances match what chair gun comes up with .
So no matter what gun chairguns formula match the real life numbers at the different distanced he listed .
As I said in the above post once I entered the pellet weight, end distance of 50 meters and muzzle velocity at 553.5 I scrolled down on the table so I could see the fps at 50 meters I changed the BC numbers until the fps matched 416.4 the crony's fps at 50 meters . Once the 50 meter 416.4 was meet by changing the BC all the other fps 's matched the real life numbers .
Chair gun didn't know the barrel twist or what damage the pellet went through the barrel but it came up with the same numbers as the real life numbers . I think there is something to this .
If you can match real life numbers like the muzzle vel and the end distance velocity you can just enter that into chair gun and get its BC . Now if you change the fps of the muzzle vel to 912 fps and match that to the 807 fps at 30 yards like in the link of BC that someone post chair gun comes up with the BC of 0.0363 . This BC matches the 807 fps at 30 yards . The 0.0310 BC . in chairgun at 30 yard distance showed 791.9 not 807 fps .
What I'm getting at is chairgun matched every distance the same as real life flight from 553.5 to 416.4 So if chair gun got it right then I would think chairgun would get it right from 912 fps to 807 fps at 30 yards . So for real life results I would go by the chairguns BC that made the 807 fps to match with its BC number of 0.0363 because chair gun nailed the real life numbers at the 553.5 fps to 416.4 fps numbers .
Now lets just say chair gun has got it right with the BC and 553.5 = 0.0225 and 912= 0.0363 we can use chairguns BC calculator velocity box to get the BC for any FPS .
In chair gun once you entered the BC number you think is correct if you right click your pointer over the BC number it will open up a box where you can choose calclulate BC from : and then choose velocity change . I entered the 0.0363 bc number and once the window is open you can change velocity from 912 to 553.5 and the range to 50 meters and the 807 to 416.4 and then press calculate and sure enough it gave me the same BC I had that worked out in the video of 553.5 = 0.0225 . So I think the right BC for this pellet is 0.0363 at 912 fps .
With this box in chairgun once you have the correct BC at one muzzle vel you can have it for any muzzle vel with the same pellet and you can figure out the BC for every fps gun there is if you know the muzzle vel and end distance vel . Try it out in chair gun and see for your self 0.0363 set at 912 v1 30 yards and 807.0 v2 . and you will see that BC puts the pellet at 807 fps at 30 yards and it matched the videos results from the 553.5 fps gun .
-
You are correct, ChairGun can correctly calculate the BC for a given set of numbers (starting and ending velocity, and distance between them)…. However, if you calculate the BC between 900 and 800 fps, don't expect it to be correct between 700 and 600 fps.... or 500 and 400.... The drag models used just don't match our pellets closely enough.... As a pellet slows down going downrange, it's Drag Coefficient changes.... The model used (in ChairGun you should use GA for pellets, and G1 for bullets) does this as well, but not in precisely the same manner.... Since the BC is the ratio of your Cd and the Cd of the drag model used, the BC can (and usually does) change with velocity....
Now lets just say chair gun has got it right with the BC and 553.5 = 0.0225 and 912= 0.0363 we can use chairguns BC calculator velocity box to get the BC for any FPS .
This statement is only correct if you already KNOW the near and far velocities and the distance between.... If you calculate a BC of 0.0225 from your 553-416 fps measurements and then change only the MV to 912 fps and click "Calculate", Chairgun will use the BC previously calculated of 0.0225 and give a MUCH lower result than the correct number of 807 fps....
Bob
-
You are correct, ChairGun can correctly calculate the BC for a given set of numbers (starting and ending velocity, and distance between them)…. However, if you calculate the BC between 900 and 800 fps, don't expect it to be correct between 700 and 600 fps.... or 500 and 400.... The drag models used just don't match our pellets closely enough.... As a pellet slows down going downrange, it's Drag Coefficient changes.... The model used (in ChairGun you should use GA for pellets, and G1 for bullets) does this as well, but not in precisely the same manner.... Since the BC is the ratio of your Cd and the Cd of the drag model used, the BC can (and usually does) change with velocity....
Now lets just say chair gun has got it right with the BC and 553.5 = 0.0225 and 912= 0.0363 we can use chairguns BC calculator velocity box to get the BC for any FPS .
This statement is only correct if you already KNOW the near and far velocities and the distance between.... If you calculate a BC of 0.0225 from your 553-416 fps measurements and then change only the MV to 912 fps and click "Calculate", Chairgun will use the BC previously calculated of 0.0225 and give a MUCH lower result than the correct number of 807 fps....
Bob
Once you do one v1 912, one distance 30 yards one v2 807 and you get the BC of 0.0363 . All you have to do to know the BC for any distance lets say 100 yards is to do this . What you want to find out first is what is the v2 going to be at 100 yards , so you put your range at 100 your muzzle vel or v1 at 912 and scroll down to 100 yards which will be the last set of numbers look under the vel ft/s set of numbers it should be 636.2 fps at 100 yards When you open the BC calculator It should be already set with the v1 912 distance 100 yards and v2 636.2 and you will see the original BC you set at 0.0363 . You can not just press calculate because nothing will change if you do . You first have to put your pointer in a number window and click in it . This will put a line in the window once you have done this then click on the calculate button . You will now see the BC change . It should have changed to 0.0362 from 0.0363 . So now when you want to see where the pellet will land change the BC on the main screen of chairgun from 0.0363 to 0.0362 . That's how you know the BC at any distance with only knowing one v1 distance and one v2 .
Chairgun can calculate just about any pellet weight so once you enter the correct pellet weight , v1 distance and v2 I think you are going to get a really good BC number and then you can change that BC to the distance your aiming at .
I would like to see some real life pellet poi compared to what chairgun gives you using the BC it picks .
This chart https://hardairmagazine.com/ballistic-coefficients/ the BC it gives does not match what chairgun is giving you . I think chairgun is giving the correct BC and the chart is wrong .
-
If you know V1 and V2, and the distance between them, of course you will get the correct BC.... between V1 and V2....
You will NOT necessarily get the correct BC beyond the range where you measured V2, because now the average velocity is slower....
You will also NOT get the correct BC for a different pellet of a different weight....
You already stated that the BC between 553 and 416 fps was 0.0225.... and that the BC between 912 and 807 fps was 0.0363.... Using whatever method you choose, could you please tell me what the BC is starting with a muzzle velocity of 700 fps?.... how about 800 fps?.... or 1000 fps?.... How about if you used a different gun?....
Don't get me wrong, ChairGun is a great tool, I use it all the time.... but don't make assumptions.... The BC of a pellet is neither a constant, nor does it vary in any precisely predictable manner....
Bob
-
RWS guy..
What Bob is talking about is that the drag models do not fit pellets. take a look at reply #2 in this thread...it has Labradar for the .25 JSB 25.4g and 34g...
https://www.gatewaytoairguns.org/GTA/index.php?topic=93367.0 (https://www.gatewaytoairguns.org/GTA/index.php?topic=93367.0)
those drag coefficient numbers are what make up the drag model that Chairgun uses to calculate a pellets B.C./trajectory/drift... Now look at all the different drag Models and see just how different they are from a pellets drag model...
Even in the powder burner world guess what the better way of doing things is still going to be a CDM (Custom Drag Model)...
it matters at distance... and 50/100 yards with a pellet is like long distance with a PB...
http://appliedballisticsllc.com/ballistics-educational-resources/custom-drag-curves/ (http://appliedballisticsllc.com/ballistics-educational-resources/custom-drag-curves/)
Now me for now I use Chairgun for a rough estimate... then shoot a lot at different distances to learn what to expect... I personally only use a Chairgun to set zero range to maximize time at pbr... and like I said get a rough estimate of drift and drop...
-
The BC varies depending on velocity because the drag models used don't work well for pellets.... Using the G1 drag model (the most common), for the JSB Exact Jumbo 15.9 gr. it is about 0.032 at 700 fps, increases to 0.042 at 800-850 fps, and then starts dropping again, to about 0.032 at 950 fps, and then it really starts to tank above that.... The best way to find out your drop for your pellets in your gun is to shoot at various ranges and record them....
Bob
I found this chart elsewhere. I shoot 15.89 and did not know the BC for it at 870 fps.
Here you say 15.89 jsp = .042 at 800-850
The chart shows it to be closer to .032 at 870 fps.
Which is closer to being correct BC for the 15.89 at 870 fps? .04+ or .032?
(http://puu.sh/AUost/c21c50a54f.png)
-
That chart was based on measurements of BCs I did about a decade ago.... and I "smoothed" the curves when I drew that chart by hand, to show the "trends".... In fact, in the original post on the CAF Forum I stated not to trust it for exact BCs, as I took a limited number of measurements (about 4-5 different muzzle velocities per pellet) over only about 10 yards.... At that time, ChairGun was using a completely different drag model for their BC calculations, and in fact didn't even tell you which one....
ChairGun now offer a choice of ten drag models, and the GA model (which did not even exist 10 years ago) is more accurate for airgun pellets.... You can select which drag model is used in the "drop down menu" underneath the "BC" box.... If you want to see what the various drag profiles look like, right click on the border of the graph, select "Ballistics Profiles", "All Profiles", and they will all be displayed on the graph.... Note that they all share one thing in common, a HUGE increase in drag between Mach 0.8-1.2....
Since the BC is the Cd of your pellet compared to the Cd of the drag model used, when the drag model changes, so does the calculated BC.... Now that ChairGun are using a much better model, the BC doesn't vary as much as it did when I drew that chart.... but the trends are similar, just not as pronounced.... You cannot make a direct comparison between the BCs on that chart and the ones currently calculated by ChairGun….
Bob
-
It seems there would be a way to use the data on the table to predict a BC for the same pellet . once you know the BC of a low 553.5 fps and a 912 fps . Lets say you set the distance to 235 yards and you set the v1 to 912 it will show all the info down to the 553.5 fps . and then down to 416 fps . That info thats listed between 553.5 which would be right around 144 yards and the 416.4 fps which should be 232 yards wouldn't the BC info between those two distances be there ,because once the pellet hits the 553.5 fps mark all that info between down to the 416.4 fps distance should be the same as firing the gun at a crony with a 553.5 v1 down to v2 416.4 and use the distance of 232 - 144 = 88 yards . So we have that information we have the 553.5 v1 distance 88 yards and v2 416.4 because thats the distance chair gun has the pellet traveling from 553.5 to 416.4 . The BC in chair gun with that info comes out to be 0.0362 . But the real life pellet goes 55 yards from 553.5 v1 to 416.4 v2 and has a BC of 0.0225 . Why is there 33 more yards gained by a pellet between the 2 distances after its already traveled 144 yards before it even gets to the 553.5 fps mark being shot from a 912 fps gun ? I would think that the distance would be the same or less not more . If chair guns distance between the 553.5 and 416.4 would have been 55 yards then you could figure the correct BC using the distance chair gun gives you between the 2 distances . Right ? I think something is not right somewhere . You cant gain 33 yards of travel after the pellet has had 144 yards of friction on it at the 553.5 mark of travel . That 88 yards compared to 55 yards right out of the gun from 553.5 to 416.4 . To me something just does not add up .
But guess what happens when you use the BC of 0,0225 with 912 fps the BC from the 553.5 v1 distance 55 yards 416.4 v2 gave you ? That's right It gives you 89 yards at 553.4 and 144 at 415.4 fps which is 55 yards .
-
What part of "out of date" don't you get?.... That chart is over a decade old, and based on insufficient data.... I know, because I drew it.... IF you had a perfect model for the JSB 16 gr. pellet THEN you could de exactly as you propose.... but that does not exist....
I'm sorry, but you don't have a good understanding of what the BC is, how it is derived, and that is is different depending on the drag model you choose.... The bottom line is that to do what you want, you need to know the Drag Coefficient for every velocity for the 16 gr. JSB, forget about the BC, and then use that Cd to calculate the trajectory and wind drift....
I have tried my best to explain this to you and failed.... So I'll just leave you to try and figure it out on your own.... Good Luck....
Bob
-
I’m with K.O.
I just use the calculator to figure out a good guess for my near zero to max out PBZ. Then forget it and go shoot.
Ditto for anything else that shoots, and the standard military way of zeroing a rifle.
-
What part of "out of date" don't you get?.... That chart is over a decade old, and based on insufficient data....
I have tried my best to explain this to you and failed.... So I'll just leave you to try and figure it out on your own.... Good Luck....
Bob
Fine Bob don't have to be douche bag about it. Take the chart off the forum marking it as bad data so no one else makes the mistake of re-posting so called Bad data.
So his answer to simple question is to go FULL BABY and give no answer at all. Thanks for nothing Bob.
Simple question BC of JSB 15.89 (Very common round) even gave the speed of 870 fps.
Only requires simple answer like "Here ya got .xxx" done. Ranting on and on does no one any good.
-
Apparently answering the question as completely and politely as I can, many times, doesn't either.... rws45user has his own ideas, that conflicts with reality, so who am I to continue to try and change that....
"FULL BABY" and "no answer at all"?.... You obviously didn't read my FIRST reply, where I answered the OP's question as completely as possible.... back in 2015 when the thread started.... ;D
as to being a "douche bag".... ::) …. I guess you never got tired of trying to help someone who just wanted to argue?.... I have no responsibility to keep trying to do that, thank you.... I gave him many answers, he just didn't want to hear them....
Bob, I do apologize for not being clear who I was answering, you may have thought my last answer was directed at you, I assure you it was not.... The BC at 870 is probably in between 0.032 and 0.040, depending on what gun....
Bob
-
Rajod take a look at what you just posted...I does absolutely nothing to help... in fact the insults and name calling are against forum rules...
Bob just said I give up trying to explain B.C. to you... after explaining the chart he made years ago was wrong...
there are different drag model for different types of bullets flat base boat tail etc... for each drag model they draw up a specific round and it's bc is one... then they take the measurements of it's drag coefficient to make a drag model for that specific round... it's bc will match the round and be accurate for that round out of that barrel and even using a different barrel can make small and (big if the round is unstable out of that barrel) changes in actual B.C. for that same round...
so now you make that round longer and heavier but still the same type of round well then the B.C. changes because it is just a comparison to the round that the drag model is based on... that is all B.C. is...
so Maybe you can do a better job of explaining how to come up with a usable drag model for him to get the B.C. from...
It would certainly be much more helpful than your reply imo...
http://www.exteriorballistics.com/ebexplained/5th/221.cfm (http://www.exteriorballistics.com/ebexplained/5th/221.cfm)
-
Actually, the chart is not "wrong", it is simply based on a drag model that has been replaced with a better one.... All the current BC data will be just as "wrong" when we finally achieve a better one.... something long overdue....
Bob
-
well yes in a way that is what I meant because until we catch up with current tech they are both "wrong"... Even with doppler B.C. will still be different out of different barrels and such...
But it will be a much better model and estimation of how the pellet will behave... but if it is overspun to the point of dynamic instability out of a certain barrel... well then there goes the usefulness of the model... past the distance it starts spiraling...
was just trying to explain that B.C. while usefull is not the final truth... in the end you have to see how it behaves out of your barrel... choked, un-choked, smooth twist, etc...
-
100% correct.... and once a pellet starts to spiral the BC number is useless.... On the other hand, you can't hit anything with it, so it really doesn't matter.... *grin*….
Bob
-
I was talking about the jsb 15.89 pellet not every pellet made .
If you watch the video I post above . Take the numbers you see in the video for the 15.89 pellet that he list at the different distances for the 553.5 fps and ending at 416.4 at 50 meters they all are the same in the chairgun program . So his real life shooting of the pellet through the crony at the different distances match what chair gun comes up with .
So no matter what gun chairguns formula match the real life numbers at the different distanced he listed .
As I said in the above post once I entered the pellet weight, end distance of 50 meters and muzzle velocity at 553.5 I scrolled down on the table so I could see the fps at 50 meters I changed the BC numbers until the fps matched 416.4 the crony's fps at 50 meters . Once the 50 meter 416.4 was meet by changing the BC all the other fps 's matched the real life numbers .
Chair gun didn't know the barrel twist or what damage the pellet went through the barrel but it came up with the same numbers as the real life numbers . I think there is something to this .
If you can match real life numbers like the muzzle vel and the end distance velocity you can just enter that into chair gun and get its BC . Now if you change the fps of the muzzle vel to 912 fps and match that to the 807 fps at 30 yards like in the link of BC that someone post chair gun comes up with the BC of 0.0363 . This BC matches the 807 fps at 30 yards . The 0.0310 BC . in chairgun at 30 yard distance showed 791.9 not 807 fps .
What I'm getting at is chairgun matched every distance the same as real life flight from 553.5 to 416.4 So if chair gun got it right then I would think chairgun would get it right from 912 fps to 807 fps at 30 yards . So for real life results I would go by the chairguns BC that made the 807 fps to match with its BC number of 0.0363 because chair gun nailed the real life numbers at the 553.5 fps to 416.4 fps numbers .
Now lets just say chair gun has got it right with the BC and 553.5 = 0.0225 and 912= 0.0363 we can use chairguns BC calculator velocity box to get the BC for any FPS .
In chair gun once you entered the BC number you think is correct if you right click your pointer over the BC number it will open up a box where you can choose calclulate BC from : and then choose velocity change . I entered the 0.0363 bc number and once the window is open you can change velocity from 912 to 553.5 and the range to 50 meters and the 807 to 416.4 and then press calculate and sure enough it gave me the same BC I had that worked out in the video of 553.5 = 0.0225 . So I think the right BC for this pellet is 0.0363 at 912 fps .
With this box in chairgun once you have the correct BC at one muzzle vel you can have it for any muzzle vel with the same pellet and you can figure out the BC for every fps gun there is if you know the muzzle vel and end distance vel . Try it out in chair gun and see for your self 0.0363 set at 912 v1 30 yards and 807.0 v2 . and you will see that BC puts the pellet at 807 fps at 30 yards and it matched the videos results from the 553.5 fps gun .
...this stuff melts my brain but I read on to try to learn... and...
You sir(?) have the singular best avatar ever. ...reminds me of the Mrs at 26... Sometimes even the blind dog finds a bone
-
What part of "out of date" don't you get?.... That chart is over a decade old, and based on insufficient data....
I have tried my best to explain this to you and failed.... So I'll just leave you to try and figure it out on your own.... Good Luck....
Bob
Fine Bob don't have to be douche bag about it. Take the chart off the forum marking it as bad data so no one else makes the mistake of re-posting so called Bad data.
So his answer to simple question is to go FULL BABY and give no answer at all. Thanks for nothing Bob.
Simple question BC of JSB 15.89 (Very common round) even gave the speed of 870 fps.
Only requires simple answer like "Here ya got .xxx" done. Ranting on and on does no one any good.
I think what the cookie monster is saying is Just that one number that 870 fps along with the pellet weight just isn't enough info to come up with a BC because every muzzle velocity fps makes a different BC . So if you could take your crony down range to say 30 or 40 yards away stack up a few bricks in front of it so you don't hit it and see that the fps is at that distance then you can go in chair gun and right click with your arrow in side the bc box and select Velocity change once that window opens up put in 870 in the far left box then put in the distance to the center of the crony and then add the fps the crony tel;s you it is . It will always be a lower number once you have the first v1 and the distance and then the v2 entered click on calculate and it will give you a new BC number .
Do you know how to watch the flight of the pellet as it moves from the starting range to your end range and watch the pellet move from one mildot to the next mil dot all the way to the end range in chairgun using the visualization view ?
I can watch the flight of my pellet I pick from 8 yards out to where it goes out of view on the radical which is 135 yards with my gun . in the view window .
Do you know How to pick a radical in chair gun ?
I have my scope set up so that at 10 yards I use the 3rd mildot down on my radical and its dead on at 10 yards . So I go into chair gun and after you have all the scope height and stuff entered and your new BC ,pellet weight ,and fps of the gun . Then I set the blob size in the Visualization view window to 1 inch to start off with at 10 yards.
I first set my start range to zero and my end range to 10 yards .
Then I click on my zero range and adjust it up or down till the center of the yellow blob is in the center of the 3rd mil dot down just like it is in my scopes radical on my air gun , with my set up its turned out to be 16.3 yards.
Now is can see what mildot I have to use to hit something at any distance I start clicking on the + next to the end range . As I make that distance farther away I can watch the blob move up . The center of the blob is your pellet so when you get to 16.3 yards the blob is going to be in the center of your cross hair .
On my gun when I'm out to 21.7 yards I can see the blob is in the center of the first mildot above center so I know at 21.7 yards I want to use the 1st mildot above center to hit something 21.7 yards away .
At about 20 yards you will want to make the yellow blob bigger because the farther away you go the smaller the blob gets so at 20 yards you can jump it up to 5 inches or so . You want to keep the blob with in the mildot so you know where the center of your pellet is.
If you get the blob to big its hard to know where the center is and the center your pellet .
On my gun from 26.5 to 47 yards is half way between the 1st and 2nd mildot high or thats 1.5 mildots high, then it starts to drop and I can watch the pellet drop back down .
The other window you will want to keep open while your watching the pellet fly through the mildots is the intercept view window It will tell you at what mildot and 1/2 mildot distances are at a glance .
As you keep clicking on the + next to the end distance at some point your pellet is going to be dead center the cross hairs again . On my gun its 72 yards so my 2 zero points are 16.3 and 72 .
As I keep increasing the range the blob starts to get smaller again so at about 85 yards I make the blob side to 15 inches and that big enough for me to see my pellet center all the way out to 135 yards .
On my gun as I increase the distance the pellet will center back over the 3rd mildot down and at 106 yards . My 10 yard mildot is also my 106 yard mildot and you will see this happen all through the mildots range and you can see that in the intercept view .
So once you know the mildots chair gun is giving you ,you can go out and see if its right or not . The way I test the BC is I check my 2 zero distances chair gun gave me going by my 3rd mildot down 10 yard dead center setting I know is right .
You might ask why did you make the 3rd mildot down match up at 10 yards ? Because I first optically centered my scope and took a shot 10 yards away from the target . The 3rd mildot down was really close to being dead on the target so I just changed the turrets off optically center to match up the 3rd mildot down at 10 yards . At 10 yards dead on the 3rd mildot down I also have a 4 mildot down 8.9 yard and I also have a 5th mildot or radical line below the 4th mildot that 8 yards .
So this means I can have all the turret adjustments without using them up to get a zero . The straighter the tube the more accurate your going to be .
From 8 to 124 yards I'm on mildots anything past that I can start clicking . I don't because I added a HHA optimizer that has a dial that adjusts the scopes tilt so I can keep my scope cross hairs dead centered on my target out to 300 yards , but thats another story .
I set up a target at 16.3 yards away , 72 yards . and 110 yards . to see if I picked the right BC It was dead on at 16.3 yards and 72 so I knew the 0.0 273 was close but at 111 yards I should have been on my 3.5 mildot but I wasn't . I had to move the target closer to me to 110 yards . So when got back to chair gun I changed the BC till it matched my 110 and 3.5 mildot which was off only one number so every thing worked out right with 0.0272 with the 950 fps gun using 14.3 22 cal cphp . So with my gun and that pellet I use that BC only because it matched up with my gun at the 3 distances on my mildots . I probably didn't do it the right way but that BC matches all my real life distances on the mildot and the mildots in chair gun so thats BC works for me and my gun with that ammo . So I think the best way to get a good BC is to shoot at 70 and then again at 100 yards because It really didn't make a real change till I got to the 100 yard mark and beyond then you can really dial in the BC because every yard started to make a difference. With my gun anyways .
Once you know your pellet matches chair gun you can print out a scope cap reticle with the numbers on them lined up with the mildots .
-
I was talking about the jsb 15.89 pellet not every pellet made .
If you watch the video I post above . Take the numbers you see in the video for the 15.89 pellet that he list at the different distances for the 553.5 fps and ending at 416.4 at 50 meters they all are the same in the chairgun program . So his real life shooting of the pellet through the crony at the different distances match what chair gun comes up with .
So no matter what gun chairguns formula match the real life numbers at the different distanced he listed .
As I said in the above post once I entered the pellet weight, end distance of 50 meters and muzzle velocity at 553.5 I scrolled down on the table so I could see the fps at 50 meters I changed the BC numbers until the fps matched 416.4 the crony's fps at 50 meters . Once the 50 meter 416.4 was meet by changing the BC all the other fps 's matched the real life numbers .
Chair gun didn't know the barrel twist or what damage the pellet went through the barrel but it came up with the same numbers as the real life numbers . I think there is something to this .
If you can match real life numbers like the muzzle vel and the end distance velocity you can just enter that into chair gun and get its BC . Now if you change the fps of the muzzle vel to 912 fps and match that to the 807 fps at 30 yards like in the link of BC that someone post chair gun comes up with the BC of 0.0363 . This BC matches the 807 fps at 30 yards . The 0.0310 BC . in chairgun at 30 yard distance showed 791.9 not 807 fps .
What I'm getting at is chairgun matched every distance the same as real life flight from 553.5 to 416.4 So if chair gun got it right then I would think chairgun would get it right from 912 fps to 807 fps at 30 yards . So for real life results I would go by the chairguns BC that made the 807 fps to match with its BC number of 0.0363 because chair gun nailed the real life numbers at the 553.5 fps to 416.4 fps numbers .
Now lets just say chair gun has got it right with the BC and 553.5 = 0.0225 and 912= 0.0363 we can use chairguns BC calculator velocity box to get the BC for any FPS .
In chair gun once you entered the BC number you think is correct if you right click your pointer over the BC number it will open up a box where you can choose calclulate BC from : and then choose velocity change . I entered the 0.0363 bc number and once the window is open you can change velocity from 912 to 553.5 and the range to 50 meters and the 807 to 416.4 and then press calculate and sure enough it gave me the same BC I had that worked out in the video of 553.5 = 0.0225 . So I think the right BC for this pellet is 0.0363 at 912 fps .
With this box in chairgun once you have the correct BC at one muzzle vel you can have it for any muzzle vel with the same pellet and you can figure out the BC for every fps gun there is if you know the muzzle vel and end distance vel . Try it out in chair gun and see for your self 0.0363 set at 912 v1 30 yards and 807.0 v2 . and you will see that BC puts the pellet at 807 fps at 30 yards and it matched the videos results from the 553.5 fps gun .
...this stuff melts my brain but I read on to try to learn... and...
You sir(?) have the singular best avatar ever. ...reminds me of the Mrs at 26... Sometimes even the blind dog finds a bone
The original avatar moved , her butt shook when she shot lol . I'll see if I can find it . See if this works https://i.imgur.com/alM76eU.jpg
-
LMBO ;D ;D ;D
-
Apparently answering the question as completely and politely as I can, many times, doesn't either.... rws45user has his own ideas, that conflicts with reality, so who am I to continue to try and change that....
"FULL BABY" and "no answer at all"?.... You obviously didn't read my FIRST reply, where I answered the OP's question as completely as possible.... back in 2015 when the thread started.... ;D
as to being a "douche bag".... ::) …. I guess you never got tired of trying to help someone who just wanted to argue?.... I have no responsibility to keep trying to do that, thank you.... I gave him many answers, he just didn't want to hear them....
Bob, I do apologize for not being clear who I was answering, you may have thought my last answer was directed at you, I assure you it was not.... The BC at 870 is probably in between 0.032 and 0.040, depending on what gun....
Bob
Bob what are you talking about ? (rws45user has his own ideas, that conflicts with reality) I was just typing out what chair gun gave me . I was asking why chair gun gave me 2 different distances. 33 yards is a long distance to be off with 2 different BC's . I would think . I think my math is correct but check it . Would the BC you get from 553.5 fps and ending at 416.4 at 50 meters 0.0225 make 33 yards distance difference compared to using the BC you get from 912 fps to 807 fps at 30 yards 0.0363 ?
-
Your individual calculations using ChairGun are fine.... but you keep arguing that from those two you can get data that is correct at any distance or velocity.... That is not correct, and I have tried to explain that several times, without success.... I suggest you do some more research, as I simply don't have the time to continue trying to assist you.... Good Luck....
Bob
-
Your individual calculations using ChairGun are fine.... but you keep arguing that from those two you can get data that is correct at any distance or velocity.... That is not correct, and I have tried to explain that several times, without success.... I suggest you do some more research, as I simply don't have the time to continue trying to assist you.... Good Luck....
Bob
I'm not arguing I was asking why you couldn't take the data between the two see what was going on between the 2 and come up with something that would work fr every fps gun . More of a thought not arguing
-
Not to sound disrespectful or anything like that, but does anyone else find it hard to focus each time rws54user makes a post? I can't put my finger on, but there is just something about each of his posts that makes it hard to focus.
Wish I could figure out what it was. :)
-
I studied it carefully and I don't think it's a matter of whether you can put your finger on it, it's whether you should.
-
Yes careful study is what is needed.
Actually I've figured it out. It's the boots. They're in the way. ;)
-
Apparently answering the question as completely and politely as I can, many times, doesn't either.... rws45user has his own ideas, that conflicts with reality, so who am I to continue to try and change that....
"FULL BABY" and "no answer at all"?.... You obviously didn't read my FIRST reply, where I answered the OP's question as completely as possible.... back in 2015 when the thread started.... ;D
as to being a "douche bag".... ::) …. I guess you never got tired of trying to help someone who just wanted to argue?.... I have no responsibility to keep trying to do that, thank you.... I gave him many answers, he just didn't want to hear them....
Bob, I do apologize for not being clear who I was answering, you may have thought my last answer was directed at you, I assure you it was not.... The BC at 870 is probably in between 0.032 and 0.040, depending on what gun....
Bob
Like!
Some people are pretty thin skinned, I thought you made things very clear.