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

Australia

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Aug 22, 2018
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Sydney Australia
Are you using a carbon fibre raped Barrel ?- because this was exactly the problem we faced with a Christian carbon light rifle regardless of what we dialed we couldn't get it to print on target - no matter what Balistic calculater we had the rifle simply wouldn't shoot in the same spot
 

entoptics

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Jan 16, 2018
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539
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.
:eek:

This is not how this works.

The 498 you get from a 5° incline at 500 yards LOS distance, is the horizontal component, over which gravity is accelerating the bullet down.

The point of impact shift is the drop the bullet would have at 500 yards minus the drop at 498 yards, and not 500 minus 498 yards!!!

The actual POI shift for a 2° incline at 500 yards with my bullet and velocity is ~0.0007 yards...or ~0.05". In other words...nothing...

I only addressed the incline issue because someone brought it up, and I wanted to be perfectly clear and rigorous in my responses. At 500 yards, in my scenario, it is completely negligible.

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.
Also, you didn't read very carefully. I did not "give my rangefinder bad data". My rangefinder doesn't calculate drops. I used LOS distance in the rangefinder, and then input the incline angle in the ballistics software. This is the most rigorous way of addressing incline, period (though as has already been pointed out, 2° is negligible at these distances anyway).

If you'd like more information on how incline affects POI, I'd suggest googling around, and/or starting a new thread on the topic.
 

corsteve

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Feb 23, 2020
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99
Location
oregon
zero ay 100 then use kentucky windage for the rest some cronos lie every gun is diff i have a 7mm/300prc can throw rocks an get a better group
 

Stgraves260

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Sep 1, 2009
Messages
605
Ok I did a little homework on the Vortex HD 5,000. That range finder does not calculate for altitude or pressure. It will only calculate between a 15 - 30 degree slope out to 400 yards. And less than a 15 degree slope out to 800 yards. LOS is your line of sight mode and your HCD is your Horizontal Component Distance. It will not give you a correction for your HCD past 800 yards. So you will need a Kestrel Applied Ballistics or something like that to give you all the corrections. You are going to have to take a class to help you understand all this. I’m not one for saying it’s impossible or can’t be done but it would be very difficult to explain all this through a text// email.
 

Stgraves260

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Sep 1, 2009
Messages
605
:eek:

This is not how this works.

The 498 you get from a 5° incline at 500 yards LOS distance, is the horizontal component, over which gravity is accelerating the bullet down.

The point of impact shift is the drop the bullet would have at 500 yards minus the drop at 498 yards, and not 500 minus 498 yards!!!

The actual POI shift for a 2° incline at 500 yards with my bullet and velocity is ~0.0007 yards...or ~0.05". In other words...nothing...

I only addressed the incline issue because someone brought it up, and I wanted to be perfectly clear and rigorous in my responses. At 500 yards, in my scenario, it is completely negligible.



Also, you didn't read very carefully. I did not "give my rangefinder bad data". My rangefinder doesn't calculate drops. I used LOS distance in the rangefinder, and then input the incline angle in the ballistics software. This is the most rigorous way of addressing incline, period (though as has already been pointed out, 2° is negligible at these distances anyway).

If you'd like more information on how incline affects POI, I'd suggest googling around, and/or starting a new thread on the topic.
this is a 4 shot group just shy of 2300 yards. I think I’m good. You asked for help, I gave it to you, you didn’t like it, so evidently you know more than me. So my question is then why are you asking for help. Good luck. Hope you can figure out what’s wrong.
 

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WiscGunner

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Aug 2, 2016
Messages
185
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.
Are correct that the shot angle is important if enough distance is involved. However you are very wrong in saying the linear distance reduction of 2yrds is equal to vertical drop. This would mean the bullet if falling at a 45* angle to target. So, you are terribly far off with respect to a 7rem mag at 500yrds but might be closer with a 45scp at 500yrds.

Yes the angle should be included if necessary. The accurate method is to enter the LOS range AND angle into the ballistic calculator so the calculator factors the full distance of environmentals on the bullet.

However, 500 yrds is not a long distance for a centerfire rifle and 2* is not a concerning angle. Certainly not for hunting and likely not even adjustable at such a short range with standard scope turrets. With the OP data entered into BallisticsARC there is a .1MOA difference between 495 and 500yrds at a 0* shot angle. The same difference exists with a 2* shot angle (34.3” of drop at 495yrds and 35.3” of drop at 500yrds).
A 10degree angle is .2moa so you could fudge it and take a click off for a 10* angled shot.
 

smokey3

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Jan 20, 2016
Messages
112
Location
WV
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.
I do not have a cosine indicator, I do have the same chart though. I guess I wasted big bucks on my G7 rangefinder. I was thinking it would calculate the needed change in yards due to the angle difference and the line of sight distance. My angle finder on my phone does the same thing as a cosine indicator I believe, maybe not though.
 

smokey3

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Jan 20, 2016
Messages
112
Location
WV
:eek:

This is not how this works.

The 498 you get from a 5° incline at 500 yards LOS distance, is the horizontal component, over which gravity is accelerating the bullet down.

The point of impact shift is the drop the bullet would have at 500 yards minus the drop at 498 yards, and not 500 minus 498 yards!!!

The actual POI shift for a 2° incline at 500 yards with my bullet and velocity is ~0.0007 yards...or ~0.05". In other words...nothing...

I only addressed the incline issue because someone brought it up, and I wanted to be perfectly clear and rigorous in my responses. At 500 yards, in my scenario, it is completely negligible.



Also, you didn't read very carefully. I did not "give my rangefinder bad data". My rangefinder doesn't calculate drops. I used LOS distance in the rangefinder, and then input the incline angle in the ballistics software. This is the most rigorous way of addressing incline, period (though as has already been pointed out, 2° is negligible at these distances anyway).

If you'd like more information on how incline affects POI, I'd suggest googling around, and/or starting a new thread on the topic.
Youtube TiborasausRex has a series of videos on this subject, very informative for understanding how the cosine factors into the equation.
 

entoptics

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Joined
Jan 16, 2018
Messages
539
this is a 4 shot group just shy of 2300 yards. I think I’m good. You asked for help, I gave it to you, you didn’t like it, so evidently you know more than me. So my question is then why are you asking for help. Good luck. Hope you can figure out what’s wrong.
That is some nice shooting at 2300 yards, but it seems to me you missed the target... ;)

Perhaps you've just explained yourself poorly, and are actually performing the calculations correctly in reality, but what you have described in your posts above is flat out incorrect. There is no debate on that front. There is also no debate that my 2° incline difference between the 200 yd and 500 yd target is not responsible for even my initial 4.5" discrepancy, let alone 6 feet.

I wasn't exactly asking for help either, more just posting up a strange curiosity I encountered. I definitely appreciate everyone's engagement and suggestions though, which will no doubt help less experienced members understand similar issues, and has resulted in an informative and fun thread.👍
 

Stgraves260

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Joined
Sep 1, 2009
Messages
605
I do not have a cosine indicator, I do have the same chart though. I guess I wasted big bucks on my G7 rangefinder. I was thinking it would calculate the needed change in yards due to the angle difference and the line of sight distance. My angle finder on my phone does the same thing as a cosine indicator I believe, maybe not though.
You did not waist your money on the G7 Rangefinder. It’s very good. I’m helping several people on this forum. I thank that people are reading to many different post and are getting them confused. It’s understandable because I help so many people. I do the same thang sometimes and I have to correct myself. I use the first gen G7 Rangefinder myself. I also use a Vectronix.
 

richhymas

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Mar 3, 2012
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48
Sorry. Don’t have the patience to read all the previous comments, but I agree with confirming scope height as well as possible mirage. Also, shoot at 100, 300, 500, 700, 900 yards or so. You may find that there is a scope height that works for all of those distances. I also agree with using a 100 yard zero. Just to minimize variables. Any chance of an updraft? Confirming your findings at different distances and also shooting different locations will help nail things down.
 

entoptics

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Joined
Jan 16, 2018
Messages
539
Sorry. Don’t have the patience to read all the previous comments, but I agree with confirming scope height as well as possible mirage. Also, shoot at 100, 300, 500, 700, 900 yards or so. You may find that there is a scope height that works for all of those distances. I also agree with using a 100 yard zero. Just to minimize variables. Any chance of an updraft? Confirming your findings at different distances and also shooting different locations will help nail things down.
I've shot this load at various distances ~100 times, and the rifle/scope ~300 times, and another essentially identical rifle in 300WM ~1800 times. My skills generally behave. This load also has generally behaved, but a lot of those rounds were on steel in less than ideal conditions, or just groups looking for seating depth or velocity, so many accuracy issues weren't recorded as any more than an anecdotal piece of "data" in my own mind (unreliable).

This last effort was to really dial in for deer season, and I got a monkey wrench in the cogs. :(

I can deal with it, if by nothing else, keeping my Bambi murder to more "social distancing" friendly ranges. :)

As to the updraft idea, this occurred to me, particularly for the 2nd session last night and the 628 yard group's high offset compared to the 500 yd. It was halfway up a steep hill, and it's plausible some updraft was happening as the sun went down.

The mirage comments are also noted. Strings were slow enough and short enough (3 shots, cool, 3 shoots), that I doubt barrel mirage could account for what I saw on Monday, but there was also a little ground mirage at work, due to the sun coming in and out of the smoke.

I'm inclined to chalk this one up to multiple tiny, and nearly immeasurable tolerances, stacking in a bad way.

1/16 MOA up with mirage or wind patterns
1/16 MOA up with scope error I can't measure
1/16 MOA up with with my 200 yard zero
1/16 MOA from spin/jump affects
1/8 Rifleman error from the slight position change required to engage the 2nd target.
1/8 MOA up with random variation in the groups. Flip a coin (shoot) 100 times, and it's not hard to imagine you could find a string of 18 where high was over represented.

The above speculation accounts for a half MOA, that if conspiring in the "up" direction, could explain two groups on one day. That's why I like to shoot lots, and record my results (and not ignore misses or surprises as "outliers").
 

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