Question on trajectories

[stosh]

I am shooting a 6x47 lapua, 70 gr sierra blitzking at a chronographed 3550 fps. It is a custom rifle with a 20 moa base and nightforce 12-42x56 scope. My problem is none of the ballistics calculators I have will generate the trajectory correctly. FYI it is zeroed at 200yds and all the calculators say it should be about .75" or 3 clicks at .250"/click at 100 yds and is it exactly on. When I was in SD hunting Pdogs I set up a target at 400 yds and dialed in 12 clkicks in elevation. the gun was hitting 4" high. All my calculators say 14 clicks. So actually I only need about 8 clicks to be zeroed at 400. so am I missing something?? Does tha fact that I have a 20 oa base effect anything? I mean could I be zeroed at 200 yds on the near zero instead of the far zero? All help is appreciated!

 

[effendude]

A couple things off the top of my head...
Did the program ask the height of the scope above the bore?
Are you sure of the velocity?
Are you sure of the BC of the bullet?
Are you sure the scope tracks perfectly?

With the calculations you provided, you were only 1MOA off at 400 yards, which considering such a light bullet, winds, shooter error, etc. you were not too far off. How many shots can you place on top of each other at distance? If the bullet/rifle load won't shoot well, you won't ever get a program to plot the shots accurately.

Scott

 

[Immike]

Did you change the elevation in your program for your new location?

 

[Erik Cortina]

One more question, why do you use clicks instead of MOA?

 

[Immike]

One more question, why do you use clicks instead of MOA?

(Erik) has a good point. For any field shooting I use moa in short hand : 12.1 , 15. 4 and so on. For me it correlates better with my scope adjustments and yardage ranging. Even though the scope is not capable of 1/10 it is a predictable formula for me and closer for my quick notes.

 

[CPorter]

Are you using a G1 or a G7 coefficient? If using the G1 that is part of the problem.

With a 20 moa rail I think your scope only has 5 moa of down adjustment left. The closer scope adjustments get to their end of travel the smaller the click increments start getting. Quality scopes might be less affected but they are affected. Bryan Litz describes a tall target test in his book. Basically a target with a 30 inch vertical line calibrated with a level or plumb line. Zero at the bottom (100 yds) then run the scope up the 30 inches and fire another group. Measure the distance between centers. Divide by the number clicks and get the adjustment factor.

 

[CJ6]

Did you program the difference in climate settings (temp/humid/wind mph,angle,Bar press,and altitude) these all play a big part in calculating zeros under different conditions and locations. But the primary is checking your zero at the yardages you plan on shooting AT the location your shooting.

 

[stosh]

All,
Thanks for the replies, here is the answers I know. I am using sierra and RCBS load data software. They both have identical results. Yes I have ran the program with and without the compensation for elevation and doesn't make much difference. I am using .25 "/click adjustments. but I am also looking at the drop tables and they are off too.

 

[Immike]

All,
Thanks for the replies, here is the answers I know. I am using sierra and RCBS load data software. They both have identical results. Yes I have ran the program with and without the compensation for elevation and doesn't make much difference. I am using .25 "/click adjustments. but I am also looking at the drop tables and they are off too.

Hi Stosh, the chronograph is not always right. You may have to adjust your speed to get on track.

 

[Webster]

Shoot one bullet at 100 yrds or 200. Give the scope 10 clicks down shoot another shot and verify what one click is worth. It's probably not exactly 0.250 MOA.

 

[effendude]

The G1-G7 difference is negligible until past 600 yards. If I recall, the blitzking is a flatbase bullet anyway.

Stosh, measure your scope height above the bore, and I will run this info thru Litz's program.
Scott

 

[expiper]

OP...shoot a group at 100 yds and either zero or measure the diff from point of aim,,,then go to 300 or further and measure the drop there ,,,,the diff will tell you your vel from the tables,,,(poor mans chrono),,,,Roger

 

[effendude]

I ran your info through Litz's program.
1.5" scope above bore: 2" scope above bore
100 .89MOA 100 .65 MOA
200 0 200 0
300 -1.62 MOA 300 -1.54 MOA
400 -3.66 MOA 400 -3.54 MOA
500 -0.14 MOA 500 -6.00 MOA

Based on this, I suspect your velocity is off or some other factor is at play
Scott

 

[stosh]

Thanks for info guys, does anyone think it's because of the 20 moa scope base??

 

[Erik Cortina]

Thanks for info guys, does anyone think it's because of the 20 moa scope base??

No

 

[MrMajestic]

I'll second the "No" ;D

 

[Ackman]

I use the ballistic computer in a Pact Pro chronograph. Actual bullet drop is right there with what the chart says. Elevation changes ballistic coefficient. So does temperature. Combine higher altitude with higher temps and you'll definitely see the effects as distance increases.