Confusing Exbal Question

[Moman]

I am using version 8.10 of the Nightforce Exbal program and shooting a 300 Win Mag at 3000 fps with a 180 gr. Accubond.

Elevation= 800 ft.
Temp= 50
RH= 50
Sight in distance= 200 yds.
I am using standard atmosphere pressure


At 675 yds it calls for 12.50 minutes.
At 1025 yds it calls for 27.25 minutes.

When shooting at the 675 yd target I am 3-4" high. When shooting at the 1025 yd target I am roughly 24" low and needed to correct the elevation to 31.00 minutes by trial and error. I tried to validate the trajectory at 675 with + 4" but then it calls for an even lower (26.00) elevation at 1025 yds. If I validate the trajectory at 1000 yds and say I am 24" low, it gives me a 29.75 elevation at 1025 which is closer but then the elevation for 675 is 13.75 which would even be higher. I am a little confused and not sure what would be the right thing to do to get both ranges right. What do you think?

 

[KQguy]

I would go out and shoot from as many different distances as possible(100 yd. incraments would be best),and record the actual drop without adjusting your scope.Then adjust the b.c. on your Exbal program until the drop chart matches your actual results.I alway's seem to have to play around B.C. #'s to get things to match up with actual field testing.

 

[AJ Peacock]

My guess would be that you're sight in distance is a little longer and your velocity is a little slower. Where did you get the velocity?

What type of group are you shooting at 200yds? Just a little bit high can really affect your 'actual' sightin distance in Exbal.

For example, 2850fps and a sight in distance of 255, puts your 675 at 13 MOA and your 1025 at 2950. This would be a pretty close match to the drops you listed in your posting.

Also, have you set your scope height exactly?

AJ

 

[Moman]

I set my scope height at 1.6" That should be pretty much on the money.

My sight in at 200 was only about 1/4" high.

The loads were chronographed with two units. But, there may be some flaw to this. I have an old Pact that shows 2890 fps, but this same load used to show 3000 fps. All components were the same, even the number of firings for the brass, same lot # of all other components. I used a friends Chrony and it showed 3016 fps. I thought 3000 would be very close to actual.

When I validate for 675 yds, the velocity changes to 3044 fps. When I validate for 1000 yds, the velocity changes to 2887 fps.

 

[Moman]

AJ, I just ran some of the numbers you were talking about through the program and see what you mean. A little here and there changes things. I am going to go back to the range and rework this from scratch.

Should I expect Exbal to be accurate at all of these ranges if the input is accurate?

 

[AJ Peacock]

AJ, I just ran some of the numbers you were talking about through the program and see what you mean. A little here and there changes things. I am going to go back to the range and rework this from scratch.

Should I expect Exbal to be accurate at all of these ranges if the input is accurate?

I've found Exbal to be very accurate when you get the inputs correct. The first thing is to get your velocity as close as possible. I have a CHRONY and it is always WAY to high. My CED M2 velocities have always made my Exbal estimates very close.

AJ

 

[Cruizin]

I guess the next thing to check is your scope. Get your rifle on a dead rest at the range and have someone dial up your scope. Make sure it is tracking correctly. 1.047" per 1 moa. After about 21 moa the .047 extra adds up to another inch. I would see if that is the case with your scope.

Box test would be a good thing to do as well.

 

[Moman]

Aj, KQ Guy, Cruizin, you guys all have some good input and ideas. I also just received an email from Gerald Perry with some good advice as well. I have been thinking about getting the CED Millenium II Chrono for some time and I think the time is now. I will have to start over with more reliable inputs and I think that will get me where I need to be. I'll check the tracking on this scope as well. Thanks guys.

 

[Michael Eichele]

Sounds to me like you are having drag model and BC issues.

After you iron out all the other variables such as your scope height and such, take your real world data and go back to your program and try different drag models (G5, G7 ect.... and different BC numbers untill your program matches your real world results. This will be your drag function and BC you will use from now on.

Also it is REALLY important to input real air conditions during your tests. If you dont have a hand held wheather station, go to the web site below and select your closest air port. This will give you the closest data. Remember too when you use air port info to select the altitude youre at and the "area pressure" NOT station pressure.