Validation question

[BallisticsGuy]

I ran through a number of simulations with BC alterations. That was most definitely not getting it there. Changing from boat tail to flat base doesn't help either. Nothing but dropping velocity to ~2650-2700 where things suddenly start to line up reasonably well at both distances. I usually look askance a bit at velocity truing because it's usually done without knowing that that's actually the issue. His chronograph was very close to the muzzle so I think there might have been an issue in data collection. We'll see.

 

[g0cherr]

I really appreciate everyone's advice. I will be going out this weekend to shoot some rounds thru the chrono set out at 10' then Check actual drop data at 100 yard increments out to 600 and we will see what that data reveals.

 

[User4302021]

I really appreciate everyone's advice. I will be going out this weekend to shoot some rounds thru the chrono set out at 10' then Check actual drop data at 100 yard increments out to 600 and we will see what that data reveals.

You have to verify your zero at the same time you shoot for distance. A variance in lighting conditions can easily make that much difference. It may not be your problem, but it is one more factor that needs eliminating to narrow down the issue.

The best light to gather dope in is either overcast, or as early in the morning as possible.

 

[J E Custom]

The reason I mentioned Bullet BCs was your desire to make the ballistic program match the actual drop table. If you adjust the powder to change the velocity The drop may match the zero at some distance so you are adjusting the drop to match the ballistic program. the problem is that it will not match at all distances because you have changed the load to match the program.

What I understood you wanted was for the program to match the actual performance of your bullet. If you change the program parameters until it matches the actual drop tables, it will be very close to the actual at all distances. If you still cant get it to match try adjusting the velocity and the bullet BC,s until you get it to match the actual drop. Both numbers may be off.

Be sure and use the G7 numbers because the old G1 numbers are not as accurate and most ballistic programs are based on the new model
G7 bullets. But Don't change your load to match the program if you want true long range accuracy from your program.

The only other thing that could cause this problem is inaccuracy in the fields of input to the program so be sure that you are putting in good data.

J E CUSTOM

 

[g0cherr]

I went out this morning and was able to zero at 100 yards and then shot a 5/8" group where POI was 1" above POA. I set up the chrono 10' in front of the gun and got a different MV than previous. 10 shots gave me an average MV of 2809 with a std deviation of 23. The 10' distance definately changed things. Unfortunately the conditions turned bad after the 300 yard group so I will have to go out again to shoot out to 600 yards and gather actual drop data. What I found already is at 300 yards with the MV of 2809 the app said to dial up 2.5 MOA but the group was still 4 1/2" low and would have required a 4 MOA adjustment to be at POA. Will be interesting to get the other data for 400, 500 and 600.

 

[live2huntelk]

[QUOTE=" I am using the Applied Ballistics app[/QUOTE]

Can you post your inputs

 

[Skimafia]

You had mentioned in a previous post the elevation you are shooting. I am curious to know if when you are taking these longer shots if the are shots at an angle up. I ran into something similar after a couple of trips to my shooting location where my dopes were off. It was a duh moment for me but I realized that I was off because my targets were at varying degrees of incline. It can make a pretty big difference in your POI.

 

[Idaho Lefty]

It sounds to me like you have the wrong Bullet BC. Bullets have different BCs at different velocities that have to be accounted for.

Try a lower BC in your program and you will see the difference. If you adjust the bullet BCs to match the actual drop It will closely match your actual drop at all distances and give you an idea of actual velocities.

J E CUSTOM

THIS ^^^ was exactly what I found out, too ! I found that, the Nosler AccuBond, 140 grain .277 dia that, has a "stated" BC of .496 to actually HAVE,.. a BC of about .485 in my .270 WSM at 3,140 FPS. I too, would suspect that, it's your Bullet that's the problem. Personally, I'd look at a "better" (more aerodynamic/ higher BC) bullet,...one that is closer, to the TRUE BC stated by the factory.

 

[BallisticsGuy]

I've been working with OP via PM's to solve his issue. The issue IS NOT BC related. If it were then the error he was seeing from 300-400 would not have appeared in a really visible way unless the BC was MASSIVELY misstated. I also tried BC's all the way down to .385 which produced results that lined up exactly nowhere. That said, G1 BC's are only valid within particular velocity windows and bullet companies like to state their BC's based on the intended use of the particular projectile which is usually a lot closer than many of us would tend to focus on. G1 like G7 is only a mathematical model. There are limits.

We've already identified a 100fps error in the initial MV due to chronograph setup and his zero range was definitely not 200yrds. When all the inputs were put in correctly the calculated drops and actual drops line up within the cone of error that comes from his group size, minor environmental changes and likely shooter error (+/- .7MOA).

 

[g0cherr]

I really appreciate the help on this. BG was able to help me correct some errors I was making along with learning the correct way to use a chronograph. This site continues to amaze and educate me. Our deer season opener is this Saturday and I am going into the field with confidence now having validated with actual shooting data out to 700 yards. Thank you

 

[BallisticsGuy]

Happy to help the folks here at LRH. Good luck on your hunt!

 

[WildRose]

I have been on this site for a few years, and the knowledge I have acquired has been a great help in getting me pointed in the right direction, learning long range shooting. I have a dilemma I can't figure out, and it is probably something I'm just overlooking so I need help. I am shooting a browning A bolt Stainless stalker in 300 WSM with a SHV Nightforce 5-20x56. I have ran it through the ladder test and it is tracking perfectly vertical, zero to 40 MOA. My load is a hand load with a consistent 5/8 group. I am shooting a Speer 180 BTSP, with Winchester cases, CCI large rifle magnum primers, and 64.5 grains of IMR 4350. Across the chrono I am getting an average of 2927 fps. 2 trips to the range for validation and i get the same results on both trips. I am using the Applied Ballistics app and have studied in detail the manual to make sure all inputs are correct (as I believe it). Here is where it gets interesting and I can't reconcile the data. I have a 200 yard zero, at 700 yards it calls for 13.75 MOA but actual shooting took 16.25 MOA scope adjustmet to zero. I entered that into the program for validation and it changes my MV to 2699. I know chronos aren't always accurate but this isn't close. So while set up, I had a great rock hillside to pick closer targets. I picked a good flat rock at 465 the new validation called for 7.5 MOA but actual shooting took 9 MOA to zero. From what i have read, BC doesn't come into play until you get out to 1000+ yards so I don't know how to reconcile these validations. No matter what I do with the MV I can't get the program to match these 2 validations, I even messed with BC, but it changed a little but not anywhere close to enough. I need help understanding what I am missing. Thanks in advance for your advice.

BC comes into play as soon as the round leaves the barrel. Worse, it degrades as velocity drops. There is no bullet stable from max V to transonic so it can make a very big difference how and at what range your BC is measured.

My guess is that there's other factors involved here such as using the wrong G1 instead of G3 or G7 BC or that your chrony has a significant error or both.

The other factor that could be screwing things up in altitude and pressure.

 

[WildRose]

i zeroed at 5100 feet and shot my validation at 4800 feet. All of those environmentals were entered in AB.

From what source? Are you using absolute, station pressure or simply an altitude input? How sure are you of the accuracy of the alt?

 

[WildRose]

Thank you for you reply. I am going to show my ignorance here and ask what True MOA and shooter MOA are?

True MOA vs the 1" at 100 general rule of thumb most people use which is off by about 4%. Not a big deal out to 400 yards but when you start pushing on out it makes a difference.

You also should consider true Ballistic Range vs LOS or straight line if you're shooting at any angle.

It's a calculated correction for any angle. No matter what the straight line distance from the shooter to the target the gravity is only acting on the bullet for the length of the bottom let of the triangle. If you're shooting at any significant up or down angle, your true ballistic range is going to be much shorter than the SL distance.