Ballistics data error.

[shahyder]

recently i took part in a shooting competition ranged at 400 yards. I was shooting a Steyr SSG 04 A1 .308 with M118 LR ammo. The problem I along with my competitors was the in correct ballistics data. The ballistics program manufactured by Jonathan Zdziarski as an iphone application showed that the bullet drops 34'' @ 400 yards. When applied this was incorrect and the real drop was about 24''. Can someone please suggest what I should do to get a relative accurate ballistics information.

P.S. same program gave correct estimations for 300 Winchester @ 400. It was only the .308 that gave us troubles

 

[Nomad47]

Get an Android based phone. Better apps.

 

[Steve Blair]

Are you sure about the muzzle velocity?

 

[brian427cobra]

Your scope doesn't adjust in inches so how far off were you in MOA/Mils? Ballistic is a first rate program, once trued I have used it to make accurate shots from 10 feet to 1780 yards, you absolutely must know your bullets speed, and your Enviromentals, I use Density Altitude, but straight temp baro altitude humidity will work, after those are a known, I adjust the BC to match my real world DOPE(Data On Previous Engagements), garbage in equals garbage out.

 

[jo191145]

Could easily be your scopes adjustments are not up to spec. Just because they say 1/8'' or 1/4'' per click that doesn't mean they actually do that. i have an older 36X Loopy that clicks 1/4'' on windage but a full 1/2'' on vertical. Was pretty amusing the first time I tried to dial in a rifle with that. It sits in a drawer now of course.
Theres plenty of free trajectory calculators on the web. Do some comparisons. If they roughly agree but your rifle does'nt you know where to look. Velocity or scope graduations. If your app is correct thats all I can think of this early in the morning.

 

[XTR]

There are several things that can combine to give you bad data, and they are cumulative.

[list type=decimal]
[*]What is your MV? If you have previously calculated it from come ups from 100 and not with a good Chrono then that is part of your error. This one could be pretty big.
[*]Scope height above bore. Can add another inch or so if it's wrong.
[*]Accurate atmospherics, if you're not using DA or entering good atmospheric data it could get you a couple of inches
[*]What BC did you run?
[*]Last but probably biggest, what scope? Here is the biggest one. The actual come up for a 175SMK to 400 yards should be in the range of 32 inches from most rifles, if your actual dope on your rifle was 24 inches then your turrets don't move what you think they do. That translates to pushing a 175SMK to about 3100FPS, and the only place that happens out of a 308 is on an internet BB
[/list]

 

[MrMajestic]

• That translates to pushing a 175SMK to about 3100FPS, and the only place that happens out of a 308 is on an internet BB

Beautiful! ;D

 

[1holeaddict]

There are several things that can combine to give you bad data, and they are cumulative.

[list type=decimal]
[*]What is your MV? If you have previously calculated it from come ups from 100 and not with a good Chrono then that is part of your error. This one could be pretty big.
[*]Scope height above bore. Can add another inch or so if it's wrong.
[*]Accurate atmospherics, if you're not using DA or entering good atmospheric data it could get you a couple of inches
[*]What BC did you run?
[*]Last but probably biggest, what scope? Here is the biggest one. The actual come up for a 175SMK to 400 yards should be in the range of 32 inches from most rifles, if your actual dope on your rifle was 24 inches then your turrets don't move what you think they do. That translates to pushing a 175SMK to about 3100FPS, and the only place that happens out of a 308 is on an internet BB
[/list]

And thats a fact Jack ??? ??? ???

 

[Laurie]

Yes,
just run the figures through Berger Bullets' / Bryan Litz's Point Mass Ballistics Solver II program using Bryan's experimentally obtained G7 BC for the 175gn Sierra MK as used in M118LR ammo. It has a pretty uninspiring G7 of 0.243 and using the nominal MV of M118LR (2,580 fps), your 100 to 400 yard 'come-up' is calculated as 36 inches under standard ballistics conditions (standard atmospheric pressure at sea level, 59-deg F temperature)

Even if you were shooting at Raton, 6,500 ft ASL and in 100-deg F temperatures, the required scope adjustment is only a couple of inches less at this relatively short distance - 1.000yd is a different matter entirely.

As XTR says, you'd need a rather 'good' MV for only 24 inches come-up - 3,049 fps for this bullet according to the Litz figures and program. There's either something wrong with your scope, or maybe your understanding of its adjustment values, or your original zero (although that would have to be wildly wrong for this amount of error, or maybe the measurement of 400 yards if the shoot took place on somewhere other than a formal rifle range - or a combination of any of these factors. (24-inches come-up is about right for 340-350 yards with these external ballistics.) The one certainty is that the program you consulted was not in error!

Anyway, it's always much better to calculate and think throughout in terms of MOA for known distance target shooting in terms of both elevation adjustment for distance and windage allowance / corrections.

 

[Nomad47]

Also don't forget that 'come up' from a 100 yard zero is not the same number as drop from line of bore.

34" of drop from line of bore and 24" of come up for a rifle that is shooting 1/2" high at 100 yards COULD be the same.

 

[shahyder]

Thank You all for your help. I will take each and everyone's advice and see what the problem was.
I was using a zeiss conquest with elevation and windage adjustment at 1/4 click = 1 MOA. My rifle was zeroed at 6 MOA @ 400yds after being zeroed @ 100yds at 0 MOA.
The range was a proper rifle range.

 

[Nomad47]

Any altitude and/or temperature difference between where you sighted in the rifle at 100 yards and the range where you shot at 400 yards?

 

[Clancy]

Your findings are real world and therefore far more useful than ballistics cards.
You must be a real rifleman because you "shot it and saw" from a real rifle at a real bench without the use of photoshop or the web. If that's where she shoots then that's where I'd sight her in.

ON THE OTHER HAND, I think your 100 yard targets will show a pretty high sight in.

BUUUUT, I've seen stranger things.

 

[drumcorpschamp]

shahyder,

For the last 2 years JBM has been my go to program for my come-ups. It has gotten me on paper every time. For me, it has been scary good out to 1000 yds.

I tried the phone app. once......

Jerry

http://www.jbmballistics.com/ballistics/calculators/calculators.shtml

 

[brian427cobra]

Thank You all for your help. I will take each and everyone's advice and see what the problem was.
I was using a zeiss conquest with elevation and windage adjustment at 1/4 click = 1 MOA. My rifle was zeroed at 6 MOA @ 400yds after being zeroed @ 100yds at 0 MOA.
The range was a proper rifle range.

No No No, 1 click which is 1/4 MOA, is nothing more than 1/4 MOA at 10 inches or 10 lightyears, and of corse everything in between, stop trying to convert a angular measurement to inches.

 

[Nomad47]

Thank You all for your help. I will take each and everyone's advice and see what the problem was.
I was using a zeiss conquest with elevation and windage adjustment at 1/4 click = 1 MOA. My rifle was zeroed at 6 MOA @ 400yds after being zeroed @ 100yds at 0 MOA.
The range was a proper rifle range.

No No No, 1 click which is 1/4 MOA, is nothing more than 1/4 MOA at 10 inches or 10 lightyears, and of corse everything in between, stop trying to convert a angular measurement to inches.

I think he meant to say 1 click is 1/4 MOA. And 6 MOA at 400 yards is 25.1328 inches - just a little over 24".

 

[shahyder]

That is correct nomad47