Help with Ballistics drop tables

[stosh]

All,

Here is the problem: Zeroed my rifle at 100yds,cronographed velocities, but my pc programs drop tables don't match my actual bullet flight, at 200 and 275yds.

Zeroed at 100yds to hit dead on at 200 requires 2 clicks up, at 275 6 clicks up.
my programs are saying I need 4 clicks up at 200yds and 8.7 at 275.
I know I am doing something wrong but can't figure it out unless it's the programs drag equation is wrong for this bullet.

6x47 Lapua, 28" 1-10 barrel, knightforce 12-42 NSX,1/4" clicks) mounted 2.25" above bore. Bullet is a Berger 88 gr Flat Base LD with a published BC of .388. Velocity is 3400.
Any help would be appreciated.


Stosh

 

[TominSWNY]

Your two click and 6 click is correct for a scope 2.5 inches above the bore.

4 and 8.7 for a scope 1.5 above the bore

 

[fireball10x]

Set your chronograph up at 100 yards check the speed with your bal program and that way you know what your bal coe is and go from there

 

[fireball10x]

It's more likely an issue with your 100 yard zero.

The bullet crosses the line of sight twice. If your 100 yard zero was the first time the line of sight and bullet path crossed then the bullet is still rising,relative to the line of sight) and the lines will intersect again at something beyond 100 yards. The ballistic programs I'm familiar with use the second intersection as the "zero". It sounds like the second time your bullet and LOS intersect is somewhere well beyond 100 yards.

As an example, using your data, if the "second" zero is at 140 yards the bullet will be 0.04" high at 100 yards which is gonna' look like zero to most folks. But, it will only be 1.2" low at 200 which is slightly more than two clicks.

I'd try a few rounds at 130-140 yards and I think you may find the bullet is either still zero or even a little high at that range compared to your 100 yard zero.

I use a 200 yard zero to try to avoid this but I just got home from a Shootin' match where I got beat like a rented mule so take this for what it may be worth.

Usually it will cross somewhere around 25 yards with a 100 yard zero and 50 with a 200.

 

[stosh]

Thanks guys, as always your very helpful.

Stosh

 

[Chuckhunter]

Stosh Tominswny is correct, change your scope height in your program and you'll see that you program clicks will match your actual clicks.

 

[stosh]

Actually I did that but didn't get me there, the only thing I can do is select a custom Drag formula for Flat Base Hollow points that gets me right on but not sure if that is going to hold true past 275, have a request in to the programmer so will see what he says.I will need to shoot paper farther out to make sure anyway but just wanted expert advice from this web site. You all have a wealth of knowledge and I am always impressed by your willingness to help another shooter.

Keep the ideas comming.
Stosh

 

[fireball10x]

Usually it will cross somewhere around 25 yards with a 100 yard zero and 50 with a 200

Not sure where you came up with that. Using Stosh's data if the bullet crossed the line of sight at 25 yards it would cross it again a somewhere between 425 and 450 yards.

Sierra Infinity software using Stosh's data says for a 100 yard zero:

Yds Path
0 : -2.25
10: -1.88
20: -1.54
30: -1.24
40: -0.96
50: -0.72
60: -0.51
70: -0.33
80: -0.19
90: -0.08
100: 0.00

For a 140 yard zero:
0 : -2.25
10: -1.88
20: -1.54
30: -1.23
40: -0.95
50: -0.70
60: -0.48
70: -0.30
80: -0.15
90: -0.04
100:+0.04
110:+0.08
120:+0.09
130:+0.06
140: 0.00

The difference between a 100 and a 140 zero is forty thousandths of an inch. Unless you're shootin' in the Houston warehouse you'll never see that.

The come up at 200 would be either 1.19" or 1.28",two clicks) with either a 100 or 140 yard zero.

Using the data for a 1.50" scope height would only make a 0.06" difference at 200 vs a 2.25" scope height.

Stosh's software is broke....... or I should say Stosh's software doesn't match what his rifle says and what Sierra's software says.

Well I was thinking of a scope on a deer rifle 1-1/2 above bore and when i sight them in average is 25 yards it crosses and 100 and a 200 yard crosses at 50 average but at 2-1/2 makes a big change it will cross at about 75 yards with a 200 yard zero and at a 100 zero it will cross at 100 and 150,It's so high it's like those see thru mounts.I sight in alot of guns and when I use standard type mounts and the gun is zeroed at 100 it's about on at 25 and at 200 yard zero it's crossing at about 50 with deer rifle velocities and scope heights