What Am I Missing?

[wkdickinson]

I have a 243 Win that shoots great. It's built on a Savage "target" action, 28" 1:8" twist Criterion, McRae chassis with a Vortex GE on top. The load I am shooting is Berger 105 hybrid, Peterson SRP, 41.0 gr of H4350 and CCI 450 primers. The load chronos at 3,165 avg. - with zero pressure signs.

My problem is, if you run a ballistics chart using Shooter or Applied Ballistics software it says with a 200 yd zero you need to come up 8.1-8.2 moa for 600 yds. I have a solid 200 yd zero. Last night I was shooting at 600 yds on an f-class target and at 8.1 moa I was up in the 8-ring, but was shooting X's at 6.75 moa up.

I assumed either my scope was not tracking correctly or my ammo was way to hot because I had changed lots of H4350 (even though there were no pressure issues). So this morning I went back to the range (a benefit of being retired ) verified my 200 yd zero, shot a "tall-target test" at 100 yds - 30 moa measured 31.625" instead of 31.41". A 0.68% error in 30 moa, so at 600 yds that would equal .06 moa or about 3/8". I also chrono'd (Magnetospeed V3) 15 rounds and got an average of 3,199 fps.

I am scratching my head! Any thoughts?

 

[jr600yd]

Forget the math. Shoot at 200 record your zero. Shoot at 600 and do the same. Life will be a lot easier.

 

[Dusty Stevens]

Are you leaving the magnetospeed on there for 600?

 

[joshb]

Thoughts? Call it an anomaly, shoot the gun and enjoy!

 

[flintcreek6412]

paper or e-target? Some will offset an e target 1 moa low to preserve the center. That will make your shots appear high on the monitor yet they are actually hitting the x downrange.

 

[Fast14riot]

Did you check your scope height measurement in the apps? A higher scope will make it seem to shoot a lot flatter.

 

[wkdickinson]

Are you leaving the magnetospeed on there for 600?

No

 

[gman47564]

is your scope height inputed correctly ? several different things can throw the applied ballistic app off... i also use applied ballistics... alot of times i will true the app with drops at knowen distances here at home... if i have everything inputted right the app is spot on... if i got something off just a little and have to true the app it will give me a little faster speed than what my magnetospeed is giving me... the bc of the bullet could be a little off at the altitude your at or the humidity could be wrong .. it all makes a difference in come ups per the app..

 

[wkdickinson]

Did you check your scope height measurement in the apps? A higher scope will make it seem to shoot a lot flatter.

Yes, scope height is correct.

 

[Fast14riot]

Did you confirm actual distance? Because about 550y/500m would be approximately 7moa for everything else staying the same.

 

[Dusty Stevens]

No

Theres your answer then. The magnetospeed causes a serious tuning difference.

 

[wkdickinson]

Theres your answer then. The magnetospeed causes a serious tuning difference.

I did not have the MS on when I shot it at 600 or for my 200 yd zero. I did have it on when I did the tall-target test.

 

[Forum Boss]

Many possible things.

1. Distance is wrong. We’ve seen some 600 yard ranges where true distance from rifle muzzle to target is closer to 580. It is also possible that your 200 yard target is not exactly 200 from your muzzle.

2. Velocity error. We once tested 5 different chronos on an in-line fixture. Same shot velocities were different with each, but consistently high or low compared to other units, even when corrected for placement. Magnetospeeds are good, but it’s not inconceivable your true velocity is 20 FPS faster.

3. Understand that Ballistics tables are just models and BC is dynamic, meaning it changes slightly at different points in flight.

It is not unusual, in my experience, with 6mm bullets, to have impacts higher than predicted at 300-600, but lower farther out.

On my 6BR running 2910 FPS MV, Ballistics table called for 2 or 3 more 1/4 MOA clicks at 600 than were actually required most days.

4. Temp and weather. Again, I have seen 1/2 MOA click variance at 600 based on temperature and foggy air alone.

As others have said you may also be inputting scope height incorrectly.

 

[wkdickinson]

Thanks for all the input from everyone. I think I will take jr600yd's suggestion to "forget the math" and just use 6.75 as my 600 yd. zero .

 

[Fast14riot]

I ran your numbers, as stated I got 8.4moa in Strelok. I corrected BC which then gave a G7 of .688 or a velocity correction of 3500fps, both are far greater than what I would consider reasonable error for 600y and 6.75moa. I'm leaning towards distance being the error.

But, as you have stated, keep a DOPE book and record your data. Thats what really matters.

 

[wkdickinson]

Thanks!

 

[XTR]

If your 200 yd zero is with the MS attached they give me about a 2 moa change up from my “naked” zero.