Velocity error in ballistics calculator possibly

[emmett]

I am trying to enjoy a rifle that I have not fired in a while but as I extend the range out to 600yds and more there is a noticeable error between the dope and the POI. When the come up given is entered into the scope the POI is a couple minutes low. The zero is good at 200yds, so my next suspect is the velocity in the calculator. This info was saved from in the calculator a few years ago and will verify it all but I was wondering if someone can tell me if my info sounds plausible or not.
I am shooting a 300 Win Mag with a 26" 4 groove Kreiger, 76.0 g H1000, WLMR primers, 210g Berger VLD Target touching the lands and am using 2930 FPS as the velocity. Does this sound close or not.

 

[clowdis]

Anything is possible but if you chrono your loads I'm sure you have seen that you have an extreme spread on your shots of anywhere from 10 to 25 FPS. Put this together with the fact that the manufacturers tend to tweak their BC's to the high side and you have nothing more than an approximation of where your shot will land in elevation.

 

[LiveFire]

What are your environmental factors? Is temperature an issue for you? Example, load developed in July at 85 deg and shooting today at 30 deg out. You might need to tweak some info in your calculator.

 

[STOMP442]

A good 100 zero is key when tuning a ballistic chart. I always zero tightly at 100 and go from there. The other thing you need to check is that you have the proper sight height entered as well as the check box that takes in your environmental factors like temp, altitude and pressure.

 

[emmett]

There is probably a 20 degree difference to the cooler side today but it seems like a small error enduced by temp. I have not made the calculation yet but it seems that a lot of velocity loss is needed to cause a 3 moa error from a 200 yd zero to 600 yd target. Maybe I am over thinking it. When I get back to my bench, I can check the info I have entered into the program and such. I did not have any problems with temperature sensitivity causing these effects on the target before when I shot the regularly. Thanks for the replies and I will look into the temp effects in detail as I work through this.

 

[emmett]

There is probably a 20 degree difference to the cooler side today but it seems like a small error enduced by temp. I have not made the calculation yet but it seems that a lot of velocity loss is needed to cause a 3 moa error from a 200 yd zero to 600 yd target. Maybe I am over thinking it. When I get back to my bench, I can check the info I have entered into the program and such. I did not have any problems with temperature sensitivity causing these effects on the target before when I shot the regularly. Thanks for the replies and I will look into the temp effects in detail as I work through this.

A good 100 zero is key when tuning a ballistic chart. I always zero tightly at 100 and go from there. The other thing you need to check is that you have the proper sight height entered as well as the check box that takes in your environmental factors like temp, altitude and pressure.

I have a good zero but at 200yds but that is in the calculator as well as the environmental data to a decent degree of accuracy. The scope height is also correct. Im afraid that the scope may be messing up.

 

[FeMan]

A general rule in truing calculators is that is your come-ups at 600 and in are wrong, its typically a bad MV input. If they are good there but re off at 800+ it is typically a bad BC.

 

[STOMP442]

Double check to make sure you are using the G7 drag model.

 

[emmett]

A general rule in truing calculators is that is your come-ups at 600 and in are wrong, its typically a bad MV input. If they are good there but re off at 800+ it is typically a bad BC.

Very good info and I will try to remember and apply it. Thanks.

 

[emmett]

Double check to make sure you are using the G7 drag model.

I did. It has come down to just a few possibilities now. The velocity in program was inadvertently changed or my scope is not adjusting the reticle accurately. This rifle, load, and calculator were proven when it was stored away a few years ago

 

[Jeff Porter]

Let’s try some Gravity Ballistics…I don’t know if this will work but let’s see. Take your 200 yard scope setting and multiply times 7.105.

See if that matches what you are seeing for true 600 scope setting for a waterline hit.

For example … 200 dope is 1.75 moa on the scope dial. 1.75x7.105 = 12.4 moa. For 600 dope.

 

[Ned Ludd]

There are many possible reasons to explain why ballistic calculator predictions may be off. It is not an uncommon event, although a 2 MOA error at 600 yd seems a bit zealous to me. Nonetheless, without a current measured velocity, there is no way to know whether that may be the input that needs correction, or it's due to something else entirely. As others have already mentioned, things that come to mind as possible explanations would include load velocity, atmospheric conditions, ballistic calculator inputs, estimated bullet BC, etc. I think you're just going to have to measure velcoity and try to get the program dialed in, or you could come at it from the other side using verified drops at various distances to provide better estimates for velocity or bullet BC.

 

[whatsupdoc]

I am shooting a 300 Win Mag with a 26" 4 groove Kreiger, 76.0 g H1000, WLMR primers, 210g Berger VLD Target touching the lands and am using 2930 FPS as the velocity. Does this sound close or not.

Where did you get the 2930 FPS number from?

The only thing that matters in your description is the 210g Berger VLD and the 2930 FPS.
You also need to enter the correct scope height and environmental variables to get close
to the correct elevation value.

Even then most of the time it is not dead on but usually its very close.

That is why we collect data because ballistic calculators are a not a substitute for real world testing.

"What is D.O.P.E? Data On Previous Engagements also known as “D.O.P.E. is a collection of ballistic data that is useful when shooting targets at various distances. In tactical and PRS style matches, this information proves to be invaluable. It provides a quick reference chart in which to dial in elevation and windage."

 

[gpoldblue]

I am trying to enjoy a rifle that I have not fired in a while but as I extend the range out to 600yds and more there is a noticeable error between the dope and the POI. When the come up given is entered into the scope the POI is a couple minutes low. The zero is good at 200yds, so my next suspect is the velocity in the calculator. This info was saved from in the calculator a few years ago and will verify it all but I was wondering if someone can tell me if my info sounds plausible or not.
I am shooting a 300 Win Mag with a 26" 4 groove Kreiger, 76.0 g H1000, WLMR primers, 210g Berger VLD Target touching the lands and am using 2930 FPS as the velocity. Does this sound close or not.

Welcome to the real world! All that data and B.C.'s are only valid in the conditions in which they were established. If any one of your conditions/parameters is different,there's where your errors are coming from. It makes a difference which direction you're shooting...up hill/down hill...altitude...air density or a combination of factors. You're learning.
Good luck and stay safe.