Let's NOT argue about BC's

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by Topshot, Feb 23, 2011.

  1. Topshot

    Topshot Well-Known Member

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    I have been following the thread "Let's argue about BC's " and oh my head hurts!

    Anyway I was thinking about all of the other things that might make a bullet appear to follow a trajectory, different from that predicted by ballistic software.

    So I thought I would come up with a top 10 list and I hope that the smart Long Range Hunters here can add to it to come up with a definitive list on how to make a good rifle shoot bad.

    1. The Shooter.
    2. Scope calibration error
    3. Chronographed velocity wrong.
    4. Parallax.
    5. wind.
    6. Mirage.
    7. Atmospheric readings wrong.
    8. Cant.
    9. Distance measurement error
    10. Variations in rifle hold, rear bag placement, recoil control, cheek weld etc between different field shooting positions.
     
  2. groper

    groper Well-Known Member

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    You forgot the Number 1 way to make a good rifle shoot bad;

    INPUTTING THE WRONG BC INTO YOUR BALLISTIC CALCULATOR TO START WITH, then fudging the other details to make your trajectory look like it fits... :rolleyes:
     

  3. Topshot

    Topshot Well-Known Member

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    Groper,
    I think that comes under the heading of trying to make a bad shooting rifle shoot well using trickery and I tend to agree with you.

    The point of this thread is to identify the things that can make a rifle that is shooting a bullet with a known B.C. not appear to follow a software predicted trajectory.
     
  4. shortgrass

    shortgrass Well-Known Member

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    I like your list. You must reside right here on Earth.
     
  5. Michael Eichele

    Michael Eichele Well-Known Member

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    Just to clarify for the newer guys, maybe you could include 'and scope height' as part of your #2 'scope calibration'. They may not make the connection.

    Just an idea.

    Thanks,

    M
     
  6. Michael Eichele

    Michael Eichele Well-Known Member

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    Kind of like you telling me to 'fudge' my velocity to make my trajectory look like it fits........even if it is 220FPS.

    :rolleyes:

    Sorry TopShot, from here, I will leave your thread alone. I will quietly take my leave and wait for my rig to be completed. Groper, feel free to flame away!!!

    M
     
    Last edited: Feb 23, 2011
  7. retiredcpo

    retiredcpo Well-Known Member

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    I read somewhere that sometimes scopes dont really move like they are supposed to.
    Most of the time 1 click moves you 1/4 inch at 100 yards I hear some scopes are off 1 click moves 3/16 insteed for each click(for example) that would throw things off
    retiredcpo
     
  8. eddybo

    eddybo Well-Known Member

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    Using G1 BCs and shooting at extreme velocities, might fall on your list somewhere.

    BTW you might make light of actually matching actual trajectories, but there are a lot of specialty bullets out there with no actual BC data available. I have been faced with that situation a few of times. Even with my jerry rigged data I have made 1K+ shots in 5 states. In one instance actual G1 BC data later became available for a bullet I was shooting with no previous data. When I introduced this new actual and probably very correct BC data into the mix that is when the problems began.

    I have started from square one a couple of tiimes on that rifle, a 338AM with a NXS trying to fix what I perceive to be a problem. I have yet to to find an answer. I would however wager that there are not many rifles that that will more reliably hit targets at 1K plus yardages, even though my drops are jerry rigged from actually shooting the rifle and not theories. Sometimes you have to bring mohammad to the mountain because the drops are what the drops are and changing BC or velocity or any thing else in your ballistic computer are going to change the actual drops shot on a single tall target moving back and shooting at increasingly longer ranges using a single POA. I still have never seen a G7 BC for that particular bullet.

    I find it disturbing that on the dozen or more rifles I shoot at long range that I do not have similar problems other than the occassional anomaly which is usually correctable with a velocity adjustment. When I say anomaly I mean that the BC for one bullet may work perfectly while another bullet in the same rifle may wander from it's anticipated path.

    Considering only vertical you can get within MOA on a 800 yard target on any given day with nothing but a BC (even a G1 BC) and a velocity estimate from quickload, not even a real chrono reading. It is only when you move into real long range or real accuracy that you have any real problems from most of the items on your list, but they do become very important.

    I took a long break from this site a couple years ago. I chose to not spend time here everyday posting when I could be out shooting, or building guns, choosing only to pop in occassionally to lurk but rarely post. I also stopped posting my hunts at that time. Participating in threads like this one and the BC thread may have been part of the reason I left in the first place. I think I am going to bow out of any further conversations on these subjects. Have fun, I have enjoyed reading all of yalls ideas on this subject.
     
  9. elkaholic

    elkaholic Well-Known Member

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    I LOVE your thread title:D. This one WAS getting a little old. There really was a lot of good info shared but COME ON GUYSlightbulb......Rich
     
  10. rscott5028

    rscott5028 Well-Known Member

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    Eddybo,

    It's all relative. I've been shooting for 40+ years. Nonetheless, I count myself as a newbie here although I may be an expert next to some other guy.

    I appreciate the insight and public scruitiny from all you guys.

    I'm sorry this has worn you down. But, it's been educational for me. ..and, much appreciated.

    What I find taxing is sorting out the real info from the BS; and the techincal minutia from what's practical.

    Internet polls and popular opinion don't make it right.

    Too many assumptions on behalf of the shooter is the biggest problem I see with BCs. I think that's pretty much broken down in items 1-10 of Topshot's list.

    Thanks!
    Richard
     
  11. 7mmHCFR

    7mmHCFR Member

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    It might be the ballistics calculator: :)

    "A ballistics software foundation rests in its ability to predict accurate trajectories, matching field results as the ultimate test. Nearly all ballistic software take for granted that a specific drag function correctly describes the drag characteristics of a bullet as related to its ballistics coefficient, consequently, whether the bullet style is a flat-based, spitzer, a boat-tail, ULD, etc they take care of them to the same drag function as indicated by the published BC, usually the G1/G7 function. The state of the art mathematical approach taken here, is quite different and a major improvement, of special application to the long range shooter."

    Patagonia Ballistics - Ballistics Software Engine
     
  12. eddybo

    eddybo Well-Known Member

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    rscott,

    The posts in that thread were educational to me also. And while I may bait and feign a little I will be the first to admit my methods are not scientific. I do not need statisitical verification of what my projectiles are doing, if I already know what they are doing by actually shooting. A drop chart in the manner in which I often prepare them served LR hunters a long time before hand held ballistic computers. Where the ballistic computer is so important to me is for calculating the effects that many variables are going to have on the recreation of those shots. If it were not for enviromental variables I would not even use a PC in the field.

    What I find to be practical may not be for others, due to time or financial constraints. I guess you are very correct as to relativity. I actually prefer for things to be correct, and to work. If I cannot make them correct, even though I have spent ten times the effort making it correct than I spend on other rifles that are correct and also work, I will settle for what works.

    I guess that I should check for errors in the complete travel of my scope, although I seldom use more than 40MOA with that gun. I thought that my ten MOA box test and the fact I have often measured the distance that one click moves groups on long range targets was sufficient maybe not. To that end I am going to pull one of the scopes and mount it on a 30/338 lapua I have almost finished putting together today. I will probably get a chance to wring it out Thursday. I am going to try the G7 with some 210s and some custom bullets for which I have no BC data. I guess it is possible that two NXS scopes could give me the same results with basically the same correction and both be wrong. Since I have basically covered every possible variable multiple times and I am guessing, only guessing that the problem must be in the scope.

    As much as I sometimes feign ignorance, most of it is not an act BTW, I do know that the bullets flight is governed by laws of physics. I understand that it is a science. I also understand that the results are only as good as the data input. While I have no desire to understand the inner principles of drag effects on a bullet other than to the extent it effects me. Often I hear people stating loads that defy logic with combinations that I have tried or with combinations that quick load predicts to be 250 fps lower than stated or 25K psi than reccomended. I do understand that maybe there are tubes out there that are faster but 250 fps faster, cmon. I have the ability to look from the outside in, and fully realize that some people will automatically think....he is doing something wrong. Those people are ususally right, but it does not stop one from playing devil's advocate. Some might consider it fihing but it is assuredly for benign purposes only to further the discussion.

    In my profession we often rely upon experts. I am sure the Bryan Litz would qualify as an expert in almost in court of the land in the field of external ballistics. I also understand that should the opposing side wish to, they could retain an expert who would criticize his methods and try to rebut his opinions. In the seemingly black and white world of science, there are always gray areas. I think most of those were touched on by some of the guys who really understand this stuff.

    I think many people will find that at times after all of their best efforts they are going to find a bullet barrel velocity combo that just is not going to perfectly fall into a perfect catagory created by a lot of zeros and ones. I have only seen tisi one instance of insanity with such a great degree of change required in the BC that I out into my computer to match the actual drops. For all of my efforts I cannot reconcile the problem, even though I have lain awake at nights pondering the problem. And yes I reconize it is a problem, in a way because my work around does take much more effort, but it is no problem as far as the effectiveness of the rifle.



    I am coming back from an extended bout with poor health, so I do wear down a little more as of late. Oh well gotta go the paint should be dry and I can get another gun out of my metal shop and over to the reloading/shooting building.

     
  13. rscott5028

    rscott5028 Well-Known Member

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    Eddybo,

    Amen.

    Thanks and good luck with the new rifle.

    --richard
     
  14. timmyatnop

    timmyatnop Well-Known Member

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    Holly smokes guys that's good info but I can't take it anymore iam gona have to go back to the optics site and see if them guys are still fighting about the best scope for under 1 k . Great info just wish I could consentrate on it better.