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

[Fiftydriver]

/ubbthreads/images/graemlins/grin.gif /ubbthreads/images/graemlins/grin.gif /ubbthreads/images/graemlins/grin.gif /ubbthreads/images/graemlins/grin.gif!!!!

Thats a funny mental image imagining tinker bell trying to catch up to a 265 gr AL RBBT at near 3500 fps!!! /ubbthreads/images/graemlins/grin.gif

Kirby Allen(50)

 

[davewilson]

50, not sure what twist you need for these bullets,i'm sure that's part of the research in progress. but i would guess even though the bullets are fairly long, you're probably spinning them a bit faster than necessary. if so this puts the bullet in a nose up condition and affects the BC until it slows down enough to let it point in the same direction that it's going.this would fall into the different BC situation which has already been mentioned. also i think you've fired way too few rounds to accurately say where the POI is at given ranges.how about a 5-10 shot group on paper to have a more accurate idea for POI.

you could always look up trigger 50 and send some through the doppler radar.i'd let you use mine but i can't seem to find it as i'm finishing the one side of the basement. /ubbthreads/images/graemlins/grin.gif

 

[E4aker]

as of earliar today midway was sold out of the 50 boxes of 300 gr. sierra's. When are the bullets you're testing going to be available to the public. I need to get my hands on about 500 of them /ubbthreads/images/graemlins/grin.gif

 

[Gustavo]

Kirby,

Could you please post the entire input dataset as well as the predicted vs. field results?

At least for an exercise could be very interesting to play some numbers

 

[Eaglet]

Kirby,

Let's do this. Would you have the info. to post it?

 

[BountyHunter]

Kirby

Go to BRcentral and PM Henry Childs. He is a ballistics guru doing testing and BC calculations all the time for new custom bullets.

Bet he can figure this out for you. I am sure that he would be interested in the consistency and quality of the wildcats bullets for the 1k guys.

BH

 

[Fiftydriver]

Gustavo and Eaglet,

Exactly how much of the output data do you want????

Here are the specs for the shooting conditions:

Alt.........................3550 ft
Temp.....................70 degree F
Bar press at alt........26.43
Humidity.................37.0%

Average muzzle velocity............3460 fps
Scope height...........................2.05"
BC used for Ballistic program.......0.92
zero range...............................100 yards

Now before someone goes and blows a gasket over the BC I listed, I am not saying this is the BC of the bullet. This is just where I started with my Ballistic program to start the process to get the generated drop chart to match up with actual trajectory. JUST A NUMBER!!!

Now with that data My handheld listed the following dial ups in MOAs for each range. I will also include the actual moas needed to hit the target consistantly at each range as well to compare the drop chart with actual bullet flight.

927 yards
predicted moa.....................12.5 moa
Actual moa.........................13.5 moa

1915 yards
Predicted moa.....................38.0
Actual moa.........................35.75

2410 yards
Predicted moa.....................56.5
Actual moa.........................54.75

3008 yards
Predicted moa.....................88.25
Actual moa.........................86

That was with my initial drop chart. As you can see, All I needed to do was play with the zero range to get the drop chart to match almost perfectly with the 1915, 2410 and 3008 yard drop figures.

On a different ballistic program I use off my main computer I developed another drop chart. Still using the standard G1 drag function at this time. All specs were the same except I tweaked the zero range until my drop numbers matched up with my actual bullet flight. Using a zero range if 335 yards, here are the predicted numbers for comparision:

927 yards
10.5 moa predicted
13.5 moa actual
difference of 3 moa

1915 yards
36.0 moa predicted
35.34 moa actual
difference of 1/4 moa

2410 yards
54.75 moa predicted
54.75 moa actual
difference of 0 moa

3008 yards
86.0 moa predicted
86.0 moa actual
Difference 0 moa

So now you can see that from ranges of 1900 to 3000 yards, the drop chart is pretty much perfect. The issue is the 3 moa difference at 927 yards.

Hope this is what your looking for. If you want the complete print out, I can do that as well but its the same numbers here, at least the ones I have solid data to compare to.

As mentioned, more testing is needed at close range. I have also been playing with the G7 drag function as well and it seems to be getting me a bit closer as well. I just need to get out and check to see if the zero is at 335 yards or where in fact the rifle is zeroed at currently, that will tell me alot and then I will shoot alot more at all ranges and just tweak here and there until my drop chart matches actual bullet flight as usual.

Kirby Allen(50)

 

[jwp475]

What ballistics program are you useing?

 

[Gustavo]

Kirby,

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.

 

[Fiftydriver]

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)

 

[Gustavo]

Kirby,

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.