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BC issues

 
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  #8  
Old 06-14-2012, 08:53 AM
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Re: BC issues

One or two long range shots at rocks isn't enough information to question or overturn the manufacturer's published BC.

...especially if you're calling it 685 yds and it turns out to be 605 and then 600 even.

You've got to get very tight with the details if you want a proven/predictable load.

Put some groups on paper with enough shots and consistency to count.

-- richard
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  #9  
Old 06-14-2012, 09:08 AM
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Re: BC issues

Quote:
Originally Posted by BB28MX View Post
. Any ideas where I am going wrong?
Most errors are in velocity from inaccurate chronographs or methods of use. Also, at that short of a distance holdover is fine but not what I feel is the most accurate method to shoot groups.

As Richard stated many groups will need to be shot and also you will need to consider the error factor of the rifle , ammo and shooter combined.

Jeff
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  #10  
Old 06-14-2012, 09:09 AM
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Re: BC issues

I have two targets set up at this range, one at 605 and one at 685. The rocks I was shooting were at 605 with a 3.8 mil hold. The milk jug was at 685 and required a 4.9 mil hold. If I replace the published bc with the bc I have come up with those dopes match perfectly. I do plan to reshoot to verify and add some farther targets to get more data as well as remeasure my scopes MILs but at this time I don't feel I'm jumping the gun to replace the published bc. Especially since if I use the published bc (as I did at the range) I am consistently high. At the range I had a 5 degree down slope that equates to so little when I used my angle adjustment calculations that I can all but ignore that part. I know this gun shoots .5 moa or better so I am ruling that out. All I keep coming up with is the bc. Hope this clears a few things up and please let me know if I have over looked something or miscalculated. Thanks again guys
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  #11  
Old 06-14-2012, 09:18 AM
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Re: BC issues

One of the guys I work with ran into a similar problem with his DPMS panther, and 175gr SMK's. I showed him JBM ballistics calc using the bullets with Litz instead of the advertised bc. became much closer. He knew what his dope was already he just didn't understand the discrepancy until then.
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Keep in mind the animals we shoot for food and display are not bullet proof. Contrary to popular belief, they bleed and die just like they did a hundred years ago. Being competent with a given rifle is far more important than impressive ballistics and poor shootability. High velocity misses never put a steak in the freezer.

Joe
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  #12  
Old 06-14-2012, 09:31 AM
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Re: BC issues

Quote:
Originally Posted by BB28MX View Post
I have two targets set up at this range, one at 605 and one at 685. The rocks I was shooting were at 605 with a 3.8 mil hold. The milk jug was at 685 and required a 4.9 mil hold. If I replace the published bc with the bc I have come up with those dopes match perfectly. I do plan to reshoot to verify and add some farther targets to get more data as well as remeasure my scopes MILs but at this time I don't feel I'm jumping the gun to replace the published bc. Especially since if I use the published bc (as I did at the range) I am consistently high. At the range I had a 5 degree down slope that equates to so little when I used my angle adjustment calculations that I can all but ignore that part. I know this gun shoots .5 moa or better so I am ruling that out. All I keep coming up with is the bc. Hope this clears a few things up and please let me know if I have over looked something or miscalculated. Thanks again guys
Sounds like you have it under control.

Like Jeff pointed out, incorrect MV is often the offender.

While you can manipulate almost any variable e.g. MV, BC, Scope height, or whatever to match your dope, when conditions change, you will be off again at longer distances if you didn't manipulate the correct variable.

Many times it comes down to a stacking issue where several small things are off by a little, but add up to a noticeable difference.

-- richard
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  #13  
Old 06-14-2012, 09:32 AM
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Re: BC issues

If you are shooting with hopes of calculating accurate drops, I strongly suggest you make your targets from paper, cardboard or wood with a very small point of aim to reduce as much error as possible. This way you have something accurate to measure to center of group from point of aim. The more groups the better.

Jeff
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  #14  
Old 06-14-2012, 09:34 AM
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Re: BC issues

If I used litz's bc of .230 I get 4.41 for 600 and 5.4 for 680... That's a huge difference from what I was shooting. If that bc is accurate something else must be off quite a bit. I might see if I can get a group at 800-900 and see if the velocity is off or if ( for reasons unknown) I should use a bc different than litz's
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