Ballistic calculators off real life drop. why?

BrentM

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Joined
Jan 10, 2013
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2,494
Location
Meridian, Idaho
Like others have said, it can be a cumulative effective. Scope tracking might be off slightly, zero range may be off slightly, scope height factor might be off.

Since the impact is low by the exact same amount but the dial up is consistent for the range I'd consider a tracking test and verifying scope height to the center of the turret to the bore line. If you use the ring center to bore its usually close enough but worth a check. You may also want to double check natural scope alignment. For example if you are zeroing off a bench and then shoot the long ranges prone the alignment can be off slightly. In addition to that I have seen bench rest velocities be a tad higher than free recoil off the ground.
 

KaSH0508

Active Member
Joined
Feb 27, 2017
Messages
37
Location
Utah
Adjust the velocity in the apps until it matches your actual clicks. I have to fine tune my loads through my guns to my ballistic app every time. I adjust velocity at 500 and then BC at 800. This works for me out to 1400 yards.
 

RandySch

Member
Joined
Mar 24, 2013
Messages
10
Using 2 diff calculators and identical bullet, bc, velocity, weather etc...

Both say for instance 3.8 moa at 300..

I’m dialing to 4 and still low.

Gun is sighted and calculated in the same weather conditions.

Same thing at 750. Having to dial up 2-3 clicks extra every time, every distance. Any ideas?

In this case it’s a 6.5 creed, lapua cases, cci br4, 139 Lapua Scenar at 2782 average. Thanks for any help.
I have had the same issue with a couple of different rifles. Both .270 Winchester. The first one, I sighted in at 200 yards at a lower elevation. When I returned to a range closer to home, which is at a higher elevation, the first few shots confirmed dead on at 200. I thought that was odd, thought my shots should be higher. When I returned to the range the next time I started shooting at 500 & 600 yards and my shots were all high. The next time I returned with newly loaded ammo, reloaded to the same specs as previously, my zero was at 225 yards. Using this as my zero I recalculated my drop chart. My shots were spot on at 500 & 600 yards.
My other rifle was also shooting high however my zero confirmed dead on at 200 yards. I did the Tall Target Test and confirmed my elevation tracking was working fine. Next I did velocity verification by shooting at 600 yards. My chrono was giving me a velocity of about 3125 for a 140gr TSX which I thought was probably close. However after I adjusted my drop chart calculations using the adjustment for the 600 yard shots I discovered my muzzle velocity to be about 3200 FPS. Revisiting the range with new drop data based on this velocity I shot at 300, 400, 500, & 600 yards and my shots were all spot on.
 

jshepherd61

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Joined
Dec 28, 2015
Messages
152
Location
Parker
Using 2 diff calculators and identical bullet, bc, velocity, weather etc...

Both say for instance 3.8 moa at 300..

I’m dialing to 4 and still low.

Gun is sighted and calculated in the same weather conditions.

Same thing at 750. Having to dial up 2-3 clicks extra every time, every distance. Any ideas?

In this case it’s a 6.5 creed, lapua cases, cci br4, 139 Lapua Scenar at 2782 average. Thanks for any help.
What calculator? I like StrelokPro and put in actual click variances to adjust accuracy in the APP settings it will really true up your calculations, especially if you start shooting out past 800 yds
 

bigngreen

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Nov 24, 2008
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8,295
Location
SW Montana
If you use a quality Chrono like a magneto speed or labradar, you use real time environmental data, you plug real verified BC numbersnand data into a decent ballistics app and your scope tracking is decent you should have no need to start tuning velocity or BC by anything meaningful till 1000+ yards. If your having to tune either of those numbers by 600 your data is no good.
My typical dial in after verifying tracking and all the measurements is to fire a few rounds from a hunting shooting possition with the magspeed, shoot for zero at 100 and go to 300 and tune my zero hight, then one reound at 600, 800, 1000, 1500 and I may tune my velocity a few feet per second between 1000 and 1500.
If your tuning big time inside 600 yards you'll find your ballistics won't move conditions well and you'll enter a teater totter effect in your tune between near and far ranges.
 

smokey3

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Jan 20, 2016
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124
Location
WV
Velocity verified with 2 chronos. 1 pro chrono 1 labradar.

Zero is not off.
I do not know which ballistic calculators that you used, but I do know that the Hornady 4DOF has a feature which allows a user to measure the actual impact distance, either high or low, and to adjust the data accordingly to match the real world ballistic data that you are realizing in the field. There is a video outlining this procedure. It is designated AXIAL FORM FACTOR and it starts at a neutral number of 1 and can be adjusted up or down for the needed corrections. It is very accurate.
 

redstar6336

New Member
Joined
Feb 5, 2012
Messages
1
Check your scope tracking, lock the rifle in a sled or vice, post a tall target with 1 MOA squares at a measured 100 yards, dial in your 300, 400, 500 and 600 yard adjustments check to see if your scope moves what you dialed in exactly. Most scopes have some adjustment flaws and a good ballistic program will allow you to fix your adjustment by a percentage of tracking error.
 
Joined
Feb 18, 2019
Messages
8
Location
Yakima WA
Have you done a tall ladder test?This in my opinion is the only way to confirm scope,and dope.

same time sorry.

+ what he said when you have gone all the way up on yardage go back down to halfway like 300 yards and see if it stays on or if your scope lost a couple clicks on the turn around.
 

DENWA

Well-Known Member
Joined
Aug 27, 2008
Messages
142
Using 2 diff calculators and identical bullet, bc, velocity, weather etc...

Both say for instance 3.8 moa at 300..

I’m dialing to 4 and still low.

Gun is sighted and calculated in the same weather conditions.

Same thing at 750. Having to dial up 2-3 clicks extra every time, every distance. Any ideas?

In this case it’s a 6.5 creed, lapua cases, cci br4, 139 Lapua Scenar at 2782 average. Thanks for any help.


Get an 8 foot 2x4 set at your zero range 100-200yds.

Aim at your zero and DIAL your scope up to every yardage from your calculator.

At least spot check some of the 300,500,600, 800 etc.

Pull out your tape measure and see if your scope is tracking.
 

rickhirsch

Member
Joined
Feb 14, 2012
Messages
9
Get an 8 foot 2x4 set at your zero range 100-200yds.

Aim at your zero and DIAL your scope up to every yardage from your calculator.

At least spot check some of the 300,500,600, 800 etc.

Pull out your tape measure and see if your scope is tracking.
 

rickhirsch

Member
Joined
Feb 14, 2012
Messages
9
had this problem yesterday it was that I left the scope height in from first rifle and
I was half a minute low from 340 to 600 change it when got home. haven't shot
yet but when I recalculated it came up a half a minute. maybe check it
 

Herr Nagler

Member
Joined
Feb 12, 2019
Messages
24
Location
Denver, CO
Your issue is quite common. The numbers that come out of a ballistic calculator are a prediction, nothing more. I would say that you are doing better than most if you are only off by 1/4 MOA at 300+ yards.

You just need to “tweak” the bc number(s) you are using to a slightly lower value until the elevation predictions that come out of your ballistic calculator match what you observe in the field and then call it good.

As other already mentioned, there are several factors like scope tracking that contribute to this common issue not the least of which is bc changes constantly in flight as velocity drops off.
 
Last edited:

Kerryt38

Active Member
Joined
Apr 11, 2014
Messages
44
If you are off 2-3 clicks at 300 and 2-3 at 750 it’s most likely body position. How much pressure you put on your shoulder or how much you load the bipod can easily make that difference. It could also be a parallax issue. Not likely it’s the app or tracking from the information you have given.
 

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