JBM question

[VA_XTC_Shooter]

Anyone else having issues selecting a bullet from the JBM library and it not populating the bullet data?

 

[jelenko]

I think JBM uses the data from the bullet unless you also modify some fields directly. I've noticed that things like BC don't change when I change the bullet.

 

[VA_XTC_Shooter]

for me the weight doesnt even change...

 

[Stumpy1]

I think that is normal -the results come out looking correct to me. I don't believe the fields have ever changed when I select a different bullet. (except the output, of course)

All that is using the simplified trajectory calculator.

Frank

 

[VA_XTC_Shooter]

I guess I don't see the point of the library if the weight, caliber, BC is not automatically input. If I have to manaully input all that data, the library is useless.

 

[Doug Beach]

You don’t have to manually input it. The calculations come out correct, it just doesn’t update the data entry screen. Pick your bullet from the library, enter velocity, etc, and go.

 

[VA_XTC_Shooter]

Ah thanks. Chalk that up to my dummy moment of the day

 

[jelenko]

Done.

 

[VA_XTC_Shooter]

OK, so now that I got that out of the way...

I am trying to make the ballistic table more accurate, as in reflect my real world zeroes.
So if I plug in my 100 yd zero, the calculator indicates I need to come up 13 MOA for 600 yards. However, in reality I need to come up 14 MOA. So between 100 and 600 yds there is a 1 MOA error, out to 1,000 yds would be even greater. So I am thinking some variable is not 100% accurate. Could be BC, my velocity, etc. I was just curious if you had a recommended approach to fine tune the trajectory table to reflect known trajectories at certain yards.

 

[Doom]

No ballistic calculator is typically going to give 100% agreement with real world ballistics. As noted, BCs and velocity are the two most usual culprits. Typically, its best to adjust velocity to match out to 600yds, and adjust BC to match beyond 600.

 

[46and2]

OK, so now that I got that out of the way...

I am trying to make the ballistic table more accurate, as in reflect my real world zeroes.
So if I plug in my 100 yd zero, the calculator indicates I need to come up 13 MOA for 600 yards. However, in reality I need to come up 14 MOA. So between 100 and 600 yds there is a 1 MOA error, out to 1,000 yds would be even greater. So I am thinking some variable is not 100% accurate. Could be BC, my velocity, etc. I was just curious if you had a recommended approach to fine tune the trajectory table to reflect known trajectories at certain yards.

That is why I use a Labradar. I calculate my bc from my velocities at the closest and longest readings.
Sometimes my BC is different than the listed BC.
Also, measure your bullets and see if they are the length in the library.

 

[jhaley]

You don’t have to manually input it. The calculations come out correct, it just doesn’t update the data entry screen. Pick your bullet from the library, enter velocity, etc, and go.

That's usually been my experience, but not always, and not now. I'm selecting Hornady 143g eld-x from the library and leaving BC, cal., and weight blank. Getting error in all three fields. I left it selected (didn't enter "none") and enter data, and got results. BUT I had entered Litz's G1 BC of .614 and the program entered a his G7 BC of .315. Isn't something wrong? At least now I have results.

 

[jelenko]

Yeah. How that page works with respect to entering values in the fields is not quite clear.
As mentioned, if you start with a clean page and just select a bullet and input a mv, you get good results.

I'm not sure what happens if you enter a value for, say, BC, delete it. Then select a new bullet from the menu.

 

[jhaley]

You don’t have to manually input it. The calculations come out correct, it just doesn’t update the data entry screen. Pick your bullet from the library, enter velocity, etc, and go.

Used library, won't calculate. I get error message asking for BC, weight, caliber. Ideas?

 

[Doug Beach]

Put the default numbers back in. It won’t use them, but it needs something in those fields. Then re select your bullet from the library. The numbers in the boxes won’t change, but the chart generated will show the correct numbers.
I don’t know why it’s this way.

 

[dusterdave173]

I ran one on 223 85.5 Berger load--It was up 12 at 600 for one rifle and up 12.5 for the other rifle --only diff was 2 inches of barrel- twist same etc--and same exact chambers -had the speed entered from just one of the barrels ( it was sooo close) The rifle that I entered the exact speed for was dead on 12.5-- hit a 4 inch clay at 600 so count me as impressed with JBM I did use the G7 info because someone mentioned that I should and had it handy from Berger

 

[Old Navy]

I have used JBM for many years now. You have to put good data in to get good out. Even the scope height above bore is important. Altitude is another one that is important. Experiment with it.