Riddle me this? Ballistic calc vs reality mismatch...

entoptics

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Jan 16, 2018
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To address various questions first...

@OutsideSeth @Stgraves260 @smokey3
The 2° slope (taken from Fury 5000) was included in the calculation (rangefinder in Line of Sight Mode, so not double counted), though it's less than 0.1" difference at 500 yds, and certainly not 6 feet. 5° incline wouldn't be 6 feet either. 6 feet in 2 yards (6 feet) would require the bullet traveling down at a 45° angle...

Smoke definitely affected range finder, but only in that I had to be careful getting a good return ("LAST" setting). I shoot at this location all the time, so I almost don't need to range the 200 and 500 targets, as I setup in the same spot (can even put the rebar stand in the same holes). I range anyway, to ensure I didn't lay my mat down a foot or two forward or back from "average".

The targets were in a line, and the rifle/bipod/bags didn't move throughout the course of fire.

Coriolis was used in Ballistic (Not an option in 4DOF or JBM), but only accounts for 0.05 MOA at 500 yds shooting east anyway.

Mentioned in OP, but folks seem to have missed it. The scope passed a box test at 100 yds a couple weeks ago. 20x12 MOA, round robin fired, correct and square within measurement error. The scope has internal levels, and I use a plumb bob on the target also, so cant isn't an issue.

Sight height was calculated from bore center, by measuring from the top of mounted scope to the bottom of barrel (stock removed), then subtracting half the scope diameter and half the barrel diameter at the measurement location. It's close enough for government work...

So...On to results of my retest yesterday...

Summary - things came closer to alignment, so the first sessions results are going into the "worrisome aberration" category, though I'm still a little concerned.

This time around, I only had time for 6 shot groups, but I fired them round robin style at 200, 500, and 628 yards. I also took 1/4 MOA off of Monday's zero, as that group was a little higher than center. With only 5-6 shots per group, the results don't have as much statistical power as I'd like, but it is what it is...

200 yard "zero" group. Missing one bullet, as I got distracted by a phone call, and failed to strip off 500 yard dope for one shot (over the top of target).
IMG_5031.JPG


This is showing ~1/4 MOA high, and is a little disturbing, as the first 3 shots are the ones in orange (0.17 MOA group), and last two printed high. Not sure if this is meaningful (intermittent scope issue?), or just within random variation. Another example of how a single 3 shot group is almost completely meaningless.

Here's the 500 yard target. Also lost one shot high due to distraction and leaving 628 yard dope on (dogs this time).

Essentially perfect agreement with software's recommendation of 6.75 MOA.
IMG_5033.JPG


And here's the 628 yard target. Software recommended ~10.25 MOA, which was dialed.
IMG_5034.JPG


This one is higher than I'd like to see at ~0.4 MOA. BC would need to go from 0.7 to ~0.8 to or velocity from 2900 to ~2950 fps account for this.

At this point, I'm out of time/bullets, so I will take this information in mind as I begin field practice. I'll probably knock another 1/4 off my zero, and add a whisker of BC to my calculations. After I accumulate a "group" of a couple dozen cold bore shots at various ranges, I can see if I'm consistently high/low and adjust my DOPE accordingly. Assuming Bambi even presents himself at a distance beyond 500 yds...
 

smokey3

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My 260 Remington with 140 grain Berger’s have 24.75 MOA’s of drop. But convert that to inches it’s like 259”. People get stuck on the MOA’s and Mill’s on there dope but forget about the actual inches.
The 24.75 MOA’s is for a 1000 yards? That’s 259 inches correct? I still don’t think that you would get 6 feet of drop at 500 yards with the 2 yard difference at 498 yards that you mentioned. Maybe I am missing something?
 

WiscGunner

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Aug 2, 2016
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I t
The 24.75 MOA’s is for a 1000 yards? That’s 259 inches correct? I still don’t think that you would get 6 feet of drop at 500 yards with the 2 yard difference at 498 yards that you mentioned. Maybe I am missing something?
I think he means 6ft less distance for drop to be calculationed not 6ft down
 

Frogman77

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Feb 1, 2009
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193
Op..... I think you’re splitting hairs at this point. I would be happy with what you’re seeing given the application. If you want you can further refine loads and look at eliminating fliers by brass but really single fliers here and there away from the avg group could be anything....
 

WiscGunner

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I'm no newb, but this one has me stumped al little. Went out today to really fine tune my zero and confirm drops before I start hard core "field practice" for the upcoming deer season, and I got a pretty severe disagreement with my ballistic software (Hornady 4DOF, Ballistic, and JBM online calculator).

Details...

7mm Rem Mag, 175 ELD-X, 1:8 twist, 2900 fps (30 fps ES, 9 fps SD). Bipod and bags, near perfect conditions (other than intense wildfire smoke). 70° with 0-3 mph "thermals" type breeze moving nearly 360° in map direction over the course of fire. Environmental variables changed very little over the 1 hour course of fire (72 to 68° F, 27.56 - 27.58" pressure) , confirmed with Kestrel and iPhone barometer.

Here's the 200 yard zero, with 9 shots, fired in 3 shot strings, with full cooling between strings (homemade barrel cooler).

View attachment 214123

Group is a hair over 1 MOA, which I'm just fine with (and is consistent with dozens of other measured groups). I pulled a couple of these an 1/8 or so, but unlike some statistically challenged folks, I'm not one to quote "If I do my part" or "Lucky they all missed in the same spot" 3 shot groups as the precision my rifle will achieve. This is my hunting rifle, and though I've recorded a few 1/3 MOA, 3-shot groups with it, and several 5 shot 3/4 MOA groups, that's not what we really shoot together. For ethical hunting, I want 9/10 confidence, or even 19/20. That takes big groups, and lots of them.

I digress...

Here's the 503 yd group. Same protocol, with 9 shots, 3 shot strings, fully cooled between strings.
View attachment 214130

This group is slightly better, though statistically speaking, barely so. Still perfectly happy with it. The offset to the right is most likely spin drift according to 4DOF.

This is the weird part...

Hornady 4DOF, Ballistic, and JBM online all suggest 6.7 - 6.9 MOA come up from a 200 yd zero (level) to 503 yds with a 2° incline. Taking into account the approximately 1/8 MOA offset in my 200 yd zero, that would equate to pretty much 6.5 - 6.75 MOA.

I dialed 6.75 MOA for this group, but it was 0.78 MOA high.

I've already noticed this high bias before, between 400 and 620 yds (can't go further till it rains a good bit, as there's too much fire danger to be mucking about in the other wheat stubble field). This isn't a one off "weird thing". It's relatively consistent.

So...Here's what I know...

1) Every shot went past the LabRadar. 2900 fps was average, and right in line with 50-75 other measurements of this load, and if anything, a hair on the slow side.

2) I did a box test at 100 yds a couple weeks ago with the scope (12 MOA right shoot 1 round, 20 up shoot, 12 left shoot, 20 down shoot, repeat 3X), and my scope (Sig Whiskey 5, 5-25x50) is within group size error of tracking perfectly.

3) I've used my LabRadar and JBM online to verify the BC of the 175 ELDX dozens of times. Values range from 0.680 - 0.720 G1, with an average of ~0.705 (Hornady quotes 0.689 -0.678 G1). With a carefully aimed LabRadar, I get reliable tracking out to 120-200 yds on 7mm projectiles, but usually right around 140 yds. I ran half of the 503 yd shots through the JBM calculator, and they averaged 0.695. Again, a hair on the low side.

4) I ran the BC up in my calculators until I got the right drop at 503 yds (~6.25 MOA), and it requires about a 0.85 BC.

5) I was shooting ESE, but according to Ballistic, Coriolis is only good for ~0.05 MOA at 503 yds.

So...Dubya Tee Eff?!?!
I am sure you may be doing some of this but here goes...

Sounds like you have most of the details down, some too much. Forget coriolis, spin drift and cross wind jump for now, especially at only 500yrds.

BC changes with velocity. Either use an app that allows for Banded BC or start with the middle velocity provided by Hornady on their website.
C8CB5809-DEB8-47F2-BFF2-2D8E42FD3E1C.png


I suggest G7 but depending upon the app both G1 and G7 will work if you stay consistent.
Put .343 into your calculator if it is set for G7
Put .683 into your calculator if it is set for G1

Not sure what your setup
Is but obviously. Do NOT use a lead sled. Shoot how you would shoot in the field for consistency. Use the same method for all distances to avoid variables in velocity and POA/POI shift from positions.

Get the absolute best zero you can. Guessing and rounding errors add up. 100yrd zeros are best as atmospherics don’t factor in.

Input your actual average velocity of 10 random rounds into your app to start. This avoids ignoring drift in your powder drops. 30ES is not top precision ammo but fine for 500yrd hunting

f your velocity is taken using a Labradar or Magnetospeed with proper setup, trust it. Accurately measured velocity doesn’t need to be tweaked.

Remember distance for your targets is measured from the turrets of your scope where adjustments are made and not from the muzzle or from the chronograph.

Shoot at 500 and measure the real world error from the app. Tweak the BC of the bullets to true your app. Typically only a .001 or 2.

DO NOT forget about environmentals. Too many people focus on the pressure, DA or temp change every 5 mins. Not that important. What is more important is time of day (position of light source in the sky) but not that important at only 500yds. Pay attention to this beyond 500yrds if trying to be precise.

The most important thing to pay attention to is mirage. There are 2 mirages to pay attention to. Barrel Mirage and Target Mirage.

Barrel Mirage will start on your 7Rem Mag at about 3 rounds but will vary depending upon barrel profile, suppressor, barrel color, powder choice, etc. This will cause the target image to float in the scope resulting in POI rising. This start after about 5rounds in my medium palma stainless 6.5 Creed and results in about .3” high at 100yrds. This starts at about 3rds in my 7SS steel barrel but longer in my 7SS proof barrel. Suppressors will increase barrel heat mirage. Suppressor mirage makes a suppressor cover required. I simply take a click off my dope

Target Mirage will also make your target move with the mirage waves like floating on water and will vary with ground to air temp differences.

Be sure you are not confusing Mirage with BC error.
 

Stgraves260

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Joined
Sep 1, 2009
Messages
605
To address various questions first...

@OutsideSeth @Stgraves260 @smokey3
The 2° slope (taken from Fury 5000) was included in the calculation (rangefinder in Line of Sight Mode, so not double counted), though it's less than 0.1" difference at 500 yds, and certainly not 6 feet. 5° incline wouldn't be 6 feet either. 6 feet in 2 yards (6 feet) would require the bullet traveling down at a 45° angle...

Smoke definitely affected range finder, but only in that I had to be careful getting a good return ("LAST" setting). I shoot at this location all the time, so I almost don't need to range the 200 and 500 targets, as I setup in the same spot (can even put the rebar stand in the same holes). I range anyway, to ensure I didn't lay my mat down a foot or two forward or back from "average".

The targets were in a line, and the rifle/bipod/bags didn't move throughout the course of fire.

Coriolis was used in Ballistic (Not an option in 4DOF or JBM), but only accounts for 0.05 MOA at 500 yds shooting east anyway.

Mentioned in OP, but folks seem to have missed it. The scope passed a box test at 100 yds a couple weeks ago. 20x12 MOA, round robin fired, correct and square within measurement error. The scope has internal levels, and I use a plumb bob on the target also, so cant isn't an issue.

Sight height was calculated from bore center, by measuring from the top of mounted scope to the bottom of barrel (stock removed), then subtracting half the scope diameter and half the barrel diameter at the measurement location. It's close enough for government work...

So...On to results of my retest yesterday...

Summary - things came closer to alignment, so the first sessions results are going into the "worrisome aberration" category, though I'm still a little concerned.

This time around, I only had time for 6 shot groups, but I fired them round robin style at 200, 500, and 628 yards. I also took 1/4 MOA off of Monday's zero, as that group was a little higher than center. With only 5-6 shots per group, the results don't have as much statistical power as I'd like, but it is what it is...

200 yard "zero" group. Missing one bullet, as I got distracted by a phone call, and failed to strip off 500 yard dope for one shot (over the top of target).
View attachment 214416

This is showing ~1/4 MOA high, and is a little disturbing, as the first 3 shots are the ones in orange (0.17 MOA group), and last two printed high. Not sure if this is meaningful (intermittent scope issue?), or just within random variation. Another example of how a single 3 shot group is almost completely meaningless.

Here's the 500 yard target. Also lost one shot high due to distraction and leaving 628 yard dope on (dogs this time).

Essentially perfect agreement with software's recommendation of 6.75 MOA.
View attachment 214417

And here's the 628 yard target. Software recommended ~10.25 MOA, which was dialed.
View attachment 214418

This one is higher than I'd like to see at ~0.4 MOA. BC would need to go from 0.7 to ~0.8 to or velocity from 2900 to ~2950 fps account for this.

At this point, I'm out of time/bullets, so I will take this information in mind as I begin field practice. I'll probably knock another 1/4 off my zero, and add a whisker of BC to my calculations. After I accumulate a "group" of a couple dozen cold bore shots at various ranges, I can see if I'm consistently high/low and adjust my DOPE accordingly. Assuming Bambi even presents himself at a distance beyond 500 yds...
If your rangefinder is in (( LOS mode)) line of sight then it did not calculate for the angle. Go back to your owners manual and see what mode your rangefinder needs to be in to calculate for angle. LOS only measures straight across. Straight Line Of Sight.
 

Stgraves260

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Joined
Sep 1, 2009
Messages
605
The 24.75 MOA’s is for a 1000 yards? That’s 259 inches correct? I still don’t think that you would get 6 feet of drop at 500 yards with the 2 yard difference at 498 yards that you mentioned. Maybe I am missing something?
This would be much more easy in person. LoL!! But we are good. First part of ? Yes sir that is correct (( 24.75 MOA’s for 1,000 yards )) 2nd part of question, but with a question (( do you have a cosine indicator ? )) If so it would help explain a lot.
 

WiscGunner

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Aug 2, 2016
Messages
185
If your rangefinder is in (( LOS mode)) line of sight then it did not calculate for the angle. Go back to your owners manual and see what mode your rangefinder needs to be in to calculate for angle. LOS only measures straight across. Straight Line Of Sight.
Angle compensated ranging is for short range where environmentals aren’t important.

Line Of Sight ranging is needed to include environmentals for the actual distance the bullet will travel

input the angle in the ballistic calculator
 

WiscGunner

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Aug 2, 2016
Messages
185
Use this chart. It will help.
Nice chart but if you use an angle compensated range the you calculator will not factor weather for the real distance so this chart is really great if you are manually factoring environmentals.
 

dfanonymous

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Jul 16, 2016
Messages
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Nice chart but if you use an angle compensated range the you calculator will not factor weather for the real distance so this chart is really great if you are manually factoring environmentals.
That is a case by case thing as to what calculates what. Kestrel w/Applied ballistics will not only calculate the environments but it will calculate the density altitude change in the angle. The issue that most shooters probably run into is that once you have your correct drop for the angle, you need the true range for the wind. Again, your kestrel can do this automatically
 

Stgraves260

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Sep 1, 2009
Messages
605
I’ll use you known range and angle.
500 yards ( LOS )
Angle 2 degrees
Look at the chart where it says 5 degree then to the right under the cosine column it will say .996
Multiple your known LOS 500 yards by your cosine of .996 500 x .996 = 498 yards. Ok we know that there is 36” in a yard. So knowing that we also know that there is 72” in 2 yards.
So a 5 degree angle will change your POI ( Point of impact 72”.
So a 2.5 degree angle at 500 yards will change your POI by 36”
You see where this is going. Just 1 degree can change your POI drastically the further you shoot. That’s what i was meaning earlier when I said people don’t realize the math their ballistics range finder solver is doing.
 

Stgraves260

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Sep 1, 2009
Messages
605
What this all boils down to is if you feed your ballistics rangefinder bad data it will give you a bad firing solution. You said you were is LOS mode on your rangefinder, correct? But you were shooting at a 2 degree angle. So what you did was give your rangefinder bad data. So it’s giving you a bad firing solution.
 

dfanonymous

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Messages
1,264
I’ll use you known range and angle.
500 yards ( LOS )
Angle 2 degrees
Look at the chart where it says 5 degree then to the right under the cosine column it will say .996
Multiple your known LOS 500 yards by your cosine of .996 500 x .996 = 498 yards. Ok we know that there is 36” in a yard. So knowing that we also know that there is 72” in 2 yards.
So a 5 degree angle will change your POI ( Point of impact 72”.
So a 2.5 degree angle at 500 yards will change your POI by 36”
You see where this is going. Just 1 degree can change your POI drastically the further you shoot. That’s what i was meaning earlier when I said people don’t realize the math their ballistics range finder solver is doing.
This is also not even remotely correct.

Your POI will change 0 inches with a 2.5 degree angle while the bullet is in supersonic flight which most centerfire rifles will be at 500. Unless in your hypothetical situation you’re using a .22 that is in subsonic at that range. The bullet is going too fast to care about two yards difference at this distance with the cartridges being talked about.
 

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