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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/11/2011 at 15:24
stork23raz View Drop Down
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I have been using online free ballistic caculators for about a year now. For the past while i been using JBM, I like it. Anyway i tried the G7s, I was doing range cards for my 22. I didnt mess around with other loads. But, I did notice that the G7s elevation drop was different from the JBm. I went back and checked it several times. made sure hte all the info, bullet, twist, temp, pressure. zero, matched up. Overall the average was about 1minute difference between the two. Now for my rifle the jbm was the wone that matched.
Im just wondering why the difference is since they should both be base on physics.
What is the theory program  you all use that you find to be the most consistantly accurate to reality?
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/11/2011 at 16:53
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the difference between the G1 BC and G7 BC. most companies use G1

http://www.vortexoptics.com/content/lrbc

you have to sign up, but it's a real good "free" ballistic calc
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/11/2011 at 17:26
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Generally data plotted from doppler readings provide the real time input to computer curve fitting programs. This diminishes the need for inputs based on bc or drag functions. Other constants can be derived from this. Sierra infinity and JBM use linear coupled differential equations in numerical solvers, (generally Runga-Kutta 4th order) and iterate the output. There are different model types, some based on pt. of mass, some based on observation. An error factor will occur each time the formulas are calculated and these errors accumulate, accounting for some of your observation. Some models attribute more weight to the input variables than others.
While most outputs vary, the ability of the shooter/load/gun combo isn't tight enough to show the difference. In any case the drops as you stated is just physics, but reading the most important one, wind drift, is magic.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/11/2011 at 17:32
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Yea i was using g1 on both. I was using hte g7 cal but using g1 bC
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/11/2011 at 19:33
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I use the shooter app on my Droid. I use G7. So far with 3 rifles it has been dead on. It has a link to sync with the maps on the phone to get,most of the correct data. It was on at 1200 yards saturday. I had 3 first round hits .415 ' 750 and 1200.,its pretty simple to use.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/11/2011 at 20:15
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JBM can be a bit confusing, but it is the gold standard. I'd stick with it when you have a desktop machine or laptop available. For .22 rimfire you need to use the RA4 drag model, not G1 or G7.
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Brian Litz recommends Shooter and I believe it uses most of the same equations as JBM.  They are very similar.  I've compared them extensively and find them quite close.  Their accuracy depends upon input data.  It's best if you use chrono data.  
Obviously, the best BC data you can get would be from Weibel RADAR, but not everyone can afford that.   
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/11/2011 at 22:49
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JBM has worked well for me.

Another factor is chronograph error. 
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/12/2011 at 05:35
stork23raz View Drop Down
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Yea i dont have a smart phone. I'm  to cheap to be on a phone plan. HAHAHA
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/12/2011 at 05:42
stork23raz View Drop Down
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Originally posted by jonoMT jonoMT wrote:

JBM can be a bit confusing, but it is the gold standard. I'd stick with it when you have a desktop machine or laptop available. For .22 rimfire you need to use the RA4 drag model, not G1 or G7.

What is the RA4 model. And how would i get  a bC for  a wolf 22 target match.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/12/2011 at 08:53
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yeah the G7 BC is a mil spec (i think) and is used with G7 calcs. G1 is the industry standard and used with G1 calcs. you can google, "G7 BC, and you will find a BC comparison that aberdeen proving grounds did.

i've found that if you dont chrony then your drop estimation wont be accurate, the 2 biggest factors with bullet decent is velocity and BC.

then again i'm wrong a lot
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/12/2011 at 09:51
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stork23raz, you'll probably have a hard time finding a BC. Basically, I've just made sure everything else was as precise as could be (pressure, mv, etc) and then alternated between 100, 200 and 300 yards at the range while changing the BC number. If you limit to one variable at a time, eventually anything can be determined empirically.

jjrgr21, the G7 drag model is not really a mil spec although there are certainly military bullets that fit it. G7 is for boat tails while G1 is for flat-based bullets. In practice, you won't see much difference in drops with most bullets out to about 600 yards using either model. It is just important to know whether the BC you're using is G1 or G7. However, if possible, use the most accurate combination of model and BC. If you can get Bryan Litz' G7 BC for one of the boat tails he has tested, for example, you can pretty much take it as gospel. I trust his figures over manufacturers (except Berger, which he did).
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/12/2011 at 10:57
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Here's a post on the 'Hide with a few referenced BCs:

http://www.snipershide.com/forum/ubbthreads.php?ubb=showflat&Number=1569040

Another: http://www.rimfirecentral.com/forums/showthread.php?t=57007

However I think all these are G1. Try one that way or try it with the RA4 model. Basically, keep in mind that .22 rimfire BCs are very low and the bullets go trans-sonic, then sub-sonic very quickly. This is because the BCs are low and the MV is generally 1300 fps or less. So you've got a bullet which stability is going to be affected very quickly and a lot of drop. Maybe 338LAPUASLAP will chime in. He does a lot of rimfire out to distances most of us won't even consider.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/12/2011 at 11:31
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WEll I shoot wolf target match. its supposed to have a muzzle velocity of 1050.  So it should be about 50-100 fps below the sound barrier.  Yea i tried the other. As soon as it goes subsonic. accuracy goes out the window.

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/12/2011 at 11:57
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thanks for the correction
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/12/2011 at 21:22
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If something like a standard velocity is still giving you good groups at 100 yds (gone sub by that time) its immaterial if its supersonic at the barrel. CCI and some others can give outstanding accuracy at 100 yds, negating the need for subsonic altogethr. Most of JBM calculation will substitue the correct bc for 22 when you run the program. Time of flight is more important, outside forces have more time to act, such as wind drift.. Slow bullets with small bc, show small er diffferential rate of changes  when compared to the same percentage change of medium velocity and bc about .3, which means its really doubtful your 22 rifle/scope groups will show the difference. bc's change with velocity.

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