Calculated Trajectory VS Actual Trajectory...

[BCB]

I had QuickTarget and JBM Balistics do some simply trajectory calculation for me with my 30-40 Krag using an NOE 311-202-RN at 1760 fps (chronographed)…

QT says +2.3” at 50 yards for a 150 yard zero. JBM says +2.1” at 50 yards. These numbers are basically the same…

Yet, when I actually shoot at 150 yards with the impact of ~2.3” high at 50 yards, I am about +2.5” at 150 yards…

Both programs say I should be zeroed at 150 yards…

I wonder what happens since both programs predict virtually the same, but actual bullet path is much different…

Thanks…BCB

[plainsman456]

I am glad you aren't just taking their word for it and actually shooting at range.

How far are you normal shots?
Use that for your zero.

[JSnover]

Shoot some @ 100 yards, you'll have three data points and better idea what your actual trajectory is. JBM and QT can't account for your bore condition or the actual height of your sight/scope from bore centerline, never mind weather at your location. It all matters.

[44MAG#1]

Surely you would know the trajectory programs are just guides, right?

[BCB]

Surely you would know the trajectory programs are just guides, right?

Ahhhhh, I think I have fired enough rounds downrange to know that...

But, QuickTarget has been dang near "perfect" with its predictions on other calibers and loads...

What is interesting is the fact that both programs error nearly the same amount...

BCB

[BCB]

I just shoot to 300 yards for the most part and it is just to clang steel—Not hunting…

The pic shows where the points of impact are located at various ranges…

Note that 50 yards and 150 yards are the same—literally…

The 200 yards and 250 yards impacts are high as I was using the holdovers as per the calculations of impact points by QT and JMB…

They are all consistently high except for the 50 yard hit that is where it is to be according to QT and JMB…

Not bad consistency for impact points out to 250 yards though…

By lessening the holdover by one dot, the way it is set now would probably put them all in or at the red dot…

BCB

[Larry Gibson]

It's all about sufficient and correct data input.

Muzzle velocity must be correct. Screened velocity is not correct but can be close. Guestimated velocity is useless.

BC of bullet must be correct.

Height of sight center above bore center must be correct.

Atmospheric conditions (ambient temperature, humidity, barometric pressure) must be correct, especially for longer ranges.


If just the bullet and the velocity were supplied the different formulas probably had different setting for the other data, hence different answers.

if you use a good formula that requires the above data the results can be amazingly close even at extended long ranges. That is if you put in correct data; the old adage "garbage in, garbage out" applies.

Larry Gibson

[BCB]

Yep...

I have the correct data in QuickLoad...

I assumed that QL knows the BC of the NOE boolit?...

Velocity was chronographed...

I know atmospheric conditions can make a different, but I have never noticed the difference in holdovers that I have with this particular load...

Especially when 2 programs almost predict the same...

I changed the Height above bore by 1/2 inch (1.6" to 2.1") and it changed impact point only .1" at 100 yards and at 300 yards only .4". Not significant as I see it...

Something still a bit weird with impact points as calculated...

BCB

[BCB]

I just messed a bit with the barometric pressure. I went from 30.00 inHg to 28.00inHg and the difference was ~2" difference at 300 yards, and only .7" at 200 yards. Not significant as I see it...

BCB

[country gent]

I normally get pretty good numbers from the ballistic programs but I chronograph at 10' and another at 100 yds or farther. With the lab radar this is easy to do. I then start by using a program to calculate the actual ballistics coeffient of the bullet at that velocity to use in the program. BCs for a given bullet vary with the velocity they are running at. If you put good data in you will usually get very close.

[Cowboy_Dan]

Just checked a load for my .300 BO in JBM Ballistics with the zero set to 25 yrds (where my reflex is zeroed), and it says also zero at 150, just like your load obtains. Just funny, I guess.