How accurate is your load and bullet calculator?

[mif_slim]

Hello guys, I been toying with the JBM as well as Nikon Spot-On and Strelok app. All have about the same calculation with 0.1mil off of each other for the same bullet. However, in real world application it is really different from the numbers. For example a 168gr Nosler in 308, it reads at 550 yards it says to adjust 5mil but in real world shooting, I'm adjusting 6mil. At 625 yards, it says to adjust 6.2mil but I'm adjusting 7mil.

So my questions is, how much are you guys adjusting your real world shooting vs the bullet calculator? I know there is a lot of variables to this, but so far that is what I have confirmed with my shooting vs the calculator.

[Fjold]

Any of them will get you on paper. Typically I'm +/- 1 MOA at 1,000 yards and that changes every match, even on the same range.

The issues are in the quality of the input for the myriad of changing conditions during a shooting session. The accuracy of the calculations aren't that difficult since it's done for static conditions.

How accurate is your chronograph? Did you use an average velocity when your standard deviation was 50 fps? How accurate are your ambient conditions (barometric data, humidity, temperature) and do you check it with every shot, or use an average? You almost can't keep up with the variations in conditions.

[mif_slim]

Thanks for you response fjold. For my fps, i used average 10 shot readings. Comes to right about 2400fps (16"). Readings are abour 30fps spread so not too much difference.

But you are right, how i plugged in the data, its just the average and i think that is where the variables changes. I was just thinking if it takes me to adjust one entire mil, thats a huge miss if i didnt test my actual drop vs just printing a cheat sheet and goong out to shoot at distances.

[waveslayer]

are you using reloads or over the counter ammo? that's why most guys shooting for distance load their own to get the SD to single digits. those Calculators work well, there are others that are more accurate and will factor in for all sorts variables, ex: scope, turret error, twist rate, drift, coriolios effect, SD, temperature and powder stability with the changing air temp, etc. I would steer you to TRASOL or Applied Ballistics.

most likely your BC and MV is off giving you varied real life results. that's why the Magneto speed and Labradar are the way to go.

to answer your question direct, my apps have gotten me first round hits out to 1834 yards no problem.

[mif_slim]

Yeah, i cant say the BC is correct as Hornady released its new bullets saying their old isnt the correct BC, i dont know if Nosler has the same issues or over publish their BC to make it attrachtive for consumers. I also dont know how accurate the Chorny chrono is but thats the one i got so, i'll have to work with it.

[waveslayer]

Yeah, i cant say the BC is correct as Hornady released its new bullets saying their old isnt the correct BC, i dont know if Nosler has the same issues or over publish their BC to make it attrachtive for consumers. I also dont know how accurate the Chorny chrono is but thats the one i got so, i'll have to work with it.

that's why AB is so good, they have a bullet library with the actual BC's testes by Litz via Dopler radar. you can also do a quick Google search, what pills are you using, I might have the data for you. incorrect BC will give you big variances.

[ilawson]

Also, sight height is crucial. You are looking for the center to center dimension from the barrel's bore to the scope tube.

[mif_slim]

Im currently using the Nosler Comp 168gr HPBT.

Ilawson, i measured the bore to center scope. I know that makes a HUGE difference especially shooting at distances.

[bman940]

scope height

Agree, scope height is very important. Here's a screen shot on Nikon's Spot On Ballistic Program.

One show's 1.25 inch scope height and the other 2.5 inches.

[rero360]

I use JBM but slightly differently because I don't have a Chrono. What I do is I will zero the gun at 100 yards and then record my hit every 100 yards out to 600 (that's what is available at Angeles) then I'll go back home and plus in all the information, barrel length/twist, bullet type and weight, sight height and all that into it and then play around with the velocity numbers until it matches the data I recorded.

I have found that when I've shot at further distances that the data that JBM gives me for those other distances is pretty accurate, as in less than a mil off at 1K, which could simply be part of shooter error and all other variables.

[waveslayer]

I use JBM but slightly differently because I don't have a Chrono. What I do is I will zero the gun at 100 yards and then record my hit every 100 yards out to 600 (that's what is available at Angeles) then I'll go back home and plus in all the information, barrel length/twist, bullet type and weight, sight height and all that into it and then play around with the velocity numbers until it matches the data I recorded.

I have found that when I've shot at further distances that the data that JBM gives me for those other distances is pretty accurate, as in less than a mil off at 1K, which could simply be part of shooter error and all other variables.

Most likely BC error. That is a big factor and will Jack it up more than your velocity.

My wife thinks I have only 3 guns