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Ballistic mystery, would like your thoughts.....

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Unread 07-17-2007, 09:49 AM
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Join Date: Feb 2005
Location: USA
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What ballistics program are you useing?
range it,check the wind, dial in correction, aim and only one shot
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Unread 07-17-2007, 12:51 PM
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Join Date: Jun 2007
Location: Buenos Aires, ARGENTINA
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Thanks for your data.

I have some observations. I assumed that you've compared predicted vs. actual in-field scope corrections. Of course I'd be wrong.

1) Which value is the scope using for MOA ?

if it's using 1.0" instead of a TMOA of 1.047" that alone will acount for a 0.5 MOA difference at 925 yards,

2) Changing the ZR will only modify the relationship between the LOS and the LOF. Of course that will not change the trajectory at all ( Real DROP ). Which is another led to think that the issue could be the scope calibration or the SH value or a combination of both.

3) That's why for this type of analysis I prefer to have real Drop data expressed in linear terms. ( inches or cm )

4) Knowing the Total Dispersion at those ranges is an important value to have at hand, since it's hard to assume that group size is minimal.
regards, Gus

LoadBaseŠ Desktop & Mobile editions - the ballistics/reloading software solution
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Unread 07-17-2007, 03:02 PM
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1) The scope is a NF NXS 5.5-22 so it is set up with true moa adjustments.

The ballistic programs I have used are also set up in true moas so that should not be the issue.

Besides, if what you say is true, yes the closer range would be closer to predicted moa adjustment but the farther ranges should get much farther off as the range increases, correct???? They do not, there are right on the money from 1900 to 3000 yards.

2) When I saw that the computer generated drop chart was mirroring the actual trajectory of the bullet from 1900 to 3000 yards I simply modified the zero on the ballistic program to make bring the drop chart inline with the actual trajectory. I did not want to modify the drop chart really between those ranges because it was right on the money with what my bullet was actually doing down range.

If I put the zero at 335 yard compared to 100 yards, the bullet will impact consistantly higher over its trajectory, that was my intention and it worked perfectly. Now just have to shoot at closer range and confirm the zero.

3) It is not difficult to convert drop in moa to drop in inches is it????

4) If you figure a way to accurately measure actual bullet drop in inches at 3000 yards I would be most interested to hear it without going through a dramatic production to set up some very large back drops with a very high mounted aiming point.

Again, its easier to adjust the scope until you are hitting dead on the money and then figure the moas up from zero to that point. That is also the reason I shoot at targets which I feel are a good limit of what I expect the rifle to be able to hit accuracy wise. Generally I shoot at targets in the 1/2 moa size range, that being around 10" at 1900 yards, a foot or in diameter at 2400 yards and roughly 15" at 3000 yards. This allows me to use the target as a reference in being able to judge the size of my groups in the even I am slightly off target. IF I hit the target, I know what size groups I am shooting.

Just for an example however, at 86 moa dialed up for 3008 yards, the total drop would be 2708" roughly!!! From a 335 yard zero. TO get actual bullet drop values in inches I would need a target board roughly 226 FEET tall!!! I must be misundstanding what your trying to say because that does not even make any sense as far as practical field testing goes.

Please clearify what you mean by "Knowing the total Dispersion at those Ranges"?

Kirby Allen(50)
Kirby Allen(50)

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Unread 07-18-2007, 01:03 AM
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Join Date: Jun 2007
Location: Buenos Aires, ARGENTINA
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First of all I'm not arguing over your procedures or anything related to your equipment or else. Just trying to understand your original post.

Given that :

1) I meant to have drop in linear units, since MOA values are "coarser" and tend to change "slowly" for a given range. In other words, a linear measurement is easier to work with if we are trying to make comparisons or error analysis due to a better granularity. What I tried to say is to have computed figures in linear units. Of course, a conversion from MOA to any linear unit is feasible...

2) Of course, the difference of SMOA vs TMOA will only yield larger disagreements as range increases.

3) My comment on having the total dispersion value is in order to a have a framework from where to work out the errors then to compare them to predicted values. Having reliable values is a huge work and out of the scope of this thread, but since you are working at extreme ranges IMHO it's necessary to have that framework. Any testing of a system should include a known dispersion probability.

4) I still don't get the value of modifying the LOS/LOF relationship by changing the ZR. The curve is still the same, and as you pointed out at closer ranges the situation gets worse.

5) As you wrote, could be very useful to have more data at closer ranges, since what is happening is somehow contrary to common sense, at least from a prediction point of view.
regards, Gus

LoadBaseŠ Desktop & Mobile editions - the ballistics/reloading software solution
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