Perhaps in order of significance or likelihood, what are the factors in a ballstics app most likely to be the source of discrepancies between required actual elevation and predicted elevation? I think I can safely assume that my chrono data, ballistics model and coefficients are good to go. The shots in question was up at the Angeles range North of Los Angeles, I was shooting at their longest range targets (600 yards). My app (Shooter on Android) was computing 4.0 or 4.1 mils up. My actuals were responding way better around 4.5 up. I can certainly provide all of the gory details about the rifle, round, zero, weather, range/inclination, etc. but figured all of that is probably not required. A .308 at 600 yards should be pretty well dead nuts with an respectable ballistics app and good inputs, correct? Given the significant size of this difference I think I must have been missing something simple but significant. Thanks in advance.
- Thread starter swamp2
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Gory details matter, including scope, Muzzle velocity, any angles you inputted, etc.
If you had all the junk like SD, CE, etc, turned on, everything makes a difference in order to determine where the problem could be over the internet. We can't see you after all and have no idea what you are looking at.
If you had all the junk like SD, CE, etc, turned on, everything makes a difference in order to determine where the problem could be over the internet. We can't see you after all and have no idea what you are looking at.
-20" Remington .308, heavy barrel
-1:10 rifling
-SWFA 5-20 SS scope (have not verified travel and return to zero, trusting the manufacturer)
-100 yard zero (sub-MOA capable but typically shoots 1-2 MOA, overall not too happy with this)
-scope height: 1.85"
-Hornady TAP A-MAX 168 gr (factory ammo)
-muzzle velocity via Magnetospeed chrono: 2565 fps (standard deviation 16 fps)
-Litz BC
-G7 drag model
-zero and actual shot temp/pressure/altitude taken from nearest weather stations (max elevation of target <2000 ft)
-light to no wind (no worried about wind calculations here)
-Google earth indicates a 6° shot, used 0° at time of shots (determined very likely to be insignificant)
-Shooter app for Android (indicated 4.0 or 4.1 mils up)
-1:10 rifling
-SWFA 5-20 SS scope (have not verified travel and return to zero, trusting the manufacturer)
-100 yard zero (sub-MOA capable but typically shoots 1-2 MOA, overall not too happy with this)
-scope height: 1.85"
-Hornady TAP A-MAX 168 gr (factory ammo)
-muzzle velocity via Magnetospeed chrono: 2565 fps (standard deviation 16 fps)
-Litz BC
-G7 drag model
-zero and actual shot temp/pressure/altitude taken from nearest weather stations (max elevation of target <2000 ft)
-light to no wind (no worried about wind calculations here)
-Google earth indicates a 6° shot, used 0° at time of shots (determined very likely to be insignificant)
-Shooter app for Android (indicated 4.0 or 4.1 mils up)
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Need atmosphere to complete the calculation. Using std atoms both Ballistic AE on my iPhone and Shooter on my iPad give me 4.9 mils at 600.
Using fully manual atmospheric conditions instead of pulling them automatically and using 77 °F, 0 ft elevation and 29.92" Hg (quite a few slightly different definitions of std. conditions) still gives me 4.0 mils. Spin drift and coriolis are enabled but certainly insignificant. Being here in coastal CA and at at low elevations I figured the atmospheric conditions were not going to be the source of much variation.
Still seems to be a significant deterministic error here. Thanks much!
Still seems to be a significant deterministic error here. Thanks much!
Looks to me like several levels of fail...
what chronograph is it, because the bullet says 2650fps, though you never checked your scope, you have the junk elements turned on, and who knows what else. (Certainly your conditions sound off too ). And if you're shooting 2" at 100 at times you can be all over the map at 600. It can easily be 10" or more if not 12"+.
What you supplied says 4.8 at best.
what chronograph is it, because the bullet says 2650fps, though you never checked your scope, you have the junk elements turned on, and who knows what else. (Certainly your conditions sound off too ). And if you're shooting 2" at 100 at times you can be all over the map at 600. It can easily be 10" or more if not 12"+.
What you supplied says 4.8 at best.
Any number of possibilities here. Muzzle velocity (what makes you think it's correct?), incorrect range or angle (did you use a rangefinder?), incorrect conditions, scope not calibrated, inaccurate estimation of the actual group center and simply not enough accurate shots to form a correct conclusion.
Does an alteration to MV give correct elevation at 600 and say 300? Just because the chrono says one thing does not make it so.
How did you get the actual range? Club yardage markers? Verify the actual range.
Does an alteration to MV give correct elevation at 600 and say 300? Just because the chrono says one thing does not make it so.
How did you get the actual range? Club yardage markers? Verify the actual range.
Thanks for the cordial response on the "stupid questions" section. I perhaps mistakenly assumed that meant "no such thing as a stupid question".
I provided the Chronograph type in the OP. It is a magnetic Magnetospeed barrel mounted chrono that has been tested by the prestigious Southwest Research Institute to be within 0.4% of the more pricey/complex double skyscreen Oehler setup.
Yes, I am assuming for now that the scope tracks, that should not be a terrible assumption, but I certainly agree if something simpler cannot be found, this may require some testing and verification.
I obtained the elevation with and without some of the more advanced options (which I do understand) both on and off and simply left them on for the heck of it. It is technically a "more correct" solution even if invisible under these conditions.
This was a large 2' diameter steel plate and with the elevation from the app I could clearly see the low and reasonably consistent hits in the dirt. With the correction to 4.5 mils I had consistent hits. This was obviously not a precisely controlled paper punching exercise.
Well you know better, good luck.
I found one or more online sources for this round in the same length barrel providing a corroborating mv. I also chronoed FGMM 168 gr at 2583 (yes I know not the same powder or powder weight). Nothing perfect here but I hope to not have to invest in a big complicated chrono system. Even a change all the way up to 2600 (~+40 fps) only provides a 0.1 mil change in the predicted elevation.
I did not measure the angle at the time of shooting. Nor did I range find the target. The range claims 600 yards (semi-permanent steel) and Google earth, which shouldn't be in question, provides a range of 1801 feet (along the ground) for this target. There is certainly not 5-10+ yards error here. Again using 6°, also calculated from Google earth, shows no change in the predicted elevation value in Shooter.
See above about hits vs. misses. There was plenty enough consistency in the hits/misses (and locations tracked in the dirt for misses) for me to conclude that there was a significant discrepancy between predicted elevation and actual elevation.
I did get good elevations for the 200-400 yard targets while moving out to 600. But then again I was not shooting paper and retrieving targets which is a significant limitation. Thus I can not ultimately confirm "success" at those ranges.
Look, I fully realize I am not using absolute best practices here. I am not shooting at 2000 or even 1000 yards, nor realistically preparing to do so. I'm not trying to determine why my "groups" at 600 yards were 4" too high. There is something relatively simple that I must be missing and I'm hoping to pin it down. It seems like there is some consensus for a prediction in the 4.8-4.9 mil range (which is closer to my actuals) so the primary question is what the heck am I screwing up with the inputs into Shooter?
Thank you again for each of you running my figures through your app!
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Nope, that's why I am asking for some help.
Well, I can't get Shooter to spit out 4 mil at 600 yards Metro Std unless I run the velocity up over 2700 fps, so, you have some fundamental setup error in the application.
Wanna bet G1 BC with a G7 calculation. If you change that variable it's 4.0 to 600.
But even just as bad,
.1 mils = .36 at 100
.5 mils = 1.8" @100
1.8" x 6 = 10.8" at 600 yards
the target was 24" inches in size, so even being .5 mils off should have hit the plate.
But even just as bad,
.1 mils = .36 at 100
.5 mils = 1.8" @100
1.8" x 6 = 10.8" at 600 yards
the target was 24" inches in size, so even being .5 mils off should have hit the plate.
Thanks Cory/LL. Just before your post LL - I found the problem and it appears to be a bug in Shooter. I re-entered my round from scratch and it auto-populated a drastically different BC than the one already stored (also auto-populated upon initial entry). Again my intent was to use Litz BC with G7 model. Thus I was mixing G1/G7. In Shooter one does not get a changed BC when manually changing the drag model after the intial round set up. Feature or bug, you decide... Without carefully going through all of the other relevant details I got a 5.0 mil prediction. We're at least in the ball park here now.
Thanks but seems a fair bit off topic. Error located, it was significant. Remaining factors are ALL insignificant compared to the G1/G7 issue. I work in the engineering software simulation space and one of my motto's is "garbage in, garbage out."
The chrono was calibrated by the factory. By whom was your chrono calibrated? And do you believe that barrel harmonics affect MV to any extent greater than the natural variation of good match grade factory ammo? Not really sure of the point you are trying making here.
Never claimed nor wrote anything to the contrary. I chrono-ed my own rounds with my own rifle and double checked the values against similar to identical data "plucked off the internet" for a sanity check. The values in my app are MY measured values.
And I did VERY simple numerical experiments to verify that straight line range with or without angle, elevation and DA were NOT significant factors. This helped hone in on BC and the G1/G7 issue.
The chrono was calibrated by the factory. By whom was your chrono calibrated? And do you believe that barrel harmonics affect MV to any extent greater than the natural variation of good match grade factory ammo? Not really sure of the point you are trying making here.
Never claimed nor wrote anything to the contrary. I chrono-ed my own rounds with my own rifle and double checked the values against similar to identical data "plucked off the internet" for a sanity check. The values in my app are MY measured values.
And I did VERY simple numerical experiments to verify that straight line range with or without angle, elevation and DA were NOT significant factors. This helped hone in on BC and the G1/G7 issue.
Yeah, yeah, don't rub it in. I'm still working on consistency at 100 yards. I shoot my semi-auto (SCAR 17) much more consistently generally around 1 MOA at 100 yards. That rifle seems quite capable of out-shooting me, but unfortunately the Remington 700 perhaps doesn't, even just at 100 yards. So you're right here but only assuming absolutely no wind (it was very light and I was not dialing in any correction for it), the plate was dead on at 24.0" and of course assuming I was consistently shooting 1-2 MOA.
Well,, as a brand new user of ballistic software, this thread was helpful to me.
Thanks.
Thanks.
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