Truing a ballistic calculator

[crich]

So my recent trip to the range I decided to mess with Strelok Pro and see what It could do. I entered in all my specs into the calculator and found that my actual dope differed a little more than I expected. Keep in mind the farthest I was able to shoot this particular day was only 400yards. When I punched my actual dope in (at 400) to true the calculator it pretty much cut my BC almost in half. I messed around with a few values (scope height, velocity, weight etc) and had to make significant changes to the values to get the calculator to match what my rifle was doing. Below are the specs...

7mm mag 24"
.284 diameter
162gr
.613 BC
2940 fps (verified)
1.94 scope height.

Zeroed at 200 and a 400 target the calculator shows a 4.3 moa correction. My rifle at 400 needs 5 moa of adjustment. After trueing the calculator it changed the BC to .396 or when using fps it adjusted to 2756. These are pretty drastic which leads me to think something Im doing or inputting is off. Granted this is at 400 and my next trip I'll take it out to 1k and bump the numbers again. Anyone have any ideas on this? Seems extreme to me but Im new to the whole calculator deal.

Edit: i found and somehow missed that another member posted a very similar thread wednesday with the exact same issue as me with the same caliber and scenario (ironic as hell)... looks like the 200 yard zero might be the issue.

 

[Travis Bertrand]

I would zero at 100 and make sure it’s dead nuts. Then you will want to adjust MV for anything under 850 or so. If your dope is off past 850 then you adjust your bc.I would look at purchasing Applied ballistics end don’t look back. It’s helped me a ton. One other thing, the last rifle I got dope for, I had to drop 30fps off of it to get my ballistics to match up with real life data. If it’s more than 30, I would look at verifying everything again.

3 main ways to change dope, scope height over bore, MV and bc.


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[crich]

I would zero at 100 and make sure it’s dead nuts. Then you will want to adjust MV for anything under 850 or so. If your dope is off past 850 then you adjust your bc.I would look at purchasing Applied ballistics end don’t look back. It’s helped me a ton. One other thing, the last rifle I got dope for, I had to drop 30fps off of it to get my ballistics to match up with real life data. If it’s more than 30, I would look at verifying everything again.

3 main ways to change dope, scope height over bore, MV and bc.


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Whats the thought process behind adjusting MV or BC past a certain distance?

 

[Travis Bertrand]

The bc of the bullet doesn’t really come into effect until 850. Once your scope height is set ~+10% then that leaves one variable which is MV.

Something is way off on your inputs. I wouldn’t try to have the system correct MV or bc without multiple inputs at different yardages. And like mentioned in this thread and the other, zero at 100. Less room for error and less variables.

What bullet are you shooting?


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[Travis Bertrand]

Whats the thought process behind adjusting MV or BC past a certain distance?

Applied ballistics goes into this in detail and they have a lot of free resources online explaining why.


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[crich]

That makes sense. Im shooting factory 162 eld-x. Ive been thumbing through some of their reading material. Lots to digest but some good stuff.

 

[Travis Bertrand]

This is what applied ballistics shows roughly and at my atmospheric conditions.


I’m betting the zero is off.


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[LaHunter]

So my recent trip to the range I decided to mess with Strelok Pro and see what It could do. I entered in all my specs into the calculator and found that my actual dope differed a little more than I expected. Keep in mind the farthest I was able to shoot this particular day was only 400yards. When I punched my actual dope in (at 400) to true the calculator it pretty much cut my BC almost in half. I messed around with a few values (scope height, velocity, weight etc) and had to make significant changes to the values to get the calculator to match what my rifle was doing. Below are the specs...

7mm mag 24"
.284 diameter
162gr
.613 BC
2940 fps (verified)
1.94 scope height.

Zeroed at 200 and a 400 target the calculator shows a 4.3 moa correction. My rifle at 400 needs 5 moa of adjustment. After trueing the calculator it changed the BC to .396 or when using fps it adjusted to 2756. These are pretty drastic which leads me to think something Im doing or inputting is off. Granted this is at 400 and my next trip I'll take it out to 1k and bump the numbers again. Anyone have any ideas on this? Seems extreme to me but Im new to the whole calculator deal.

Edit: i found and somehow missed that another member posted a very similar thread wednesday with the exact same issue as me with the same caliber and scenario (ironic as hell)... looks like the 200 yard zero might be the issue.

Assuming your data is correct, this could be a scope issue. If you have a reticle that has moa hash marks, you could just use a hold over to see if this gets your POI where it should be. If holding over gets you there, it would indicate a scope adjustment issue.

 

[Wrench]

At 400 you could be off .2 on the bc and still come in better than you can shoot.

As mentioned, work velocity to 600plus and then work bc from 800 out.

If your velocity scrub is consistent to 600 the miniscule variable in bc will be quick to correct from 800-1500.

I have several rifles that will stay moa using strelok to well over 1200 yards. I have a dead coyote at 1630 as my PR so far.....using pro and a 140rdf at 3021fps.

 

[crich]

I agree with the above. Get a solid zero. 200 can work, but you should go with 100 yards - especially since you’re having problems.

First thing that jumps out is you list a G1 BC and then say your solver wants to cut it by about half. Is your solver setup for a G7 model? The 0.613 BC is based on a G1 model. If your solver is using a G7 model, it would make sense that your “needed “ BC is “about half”. A G1 model can work, but the G7 model will be better. Custom drags will be better yet.

Check that your ranges are correct and in the correct units.
Don’t use small data sets.
Don’t touch BC at 400. You really should wait until you’re in transonic.
It won’t matter at 400, but as you get further out, make sure your environmentals are correct
Shooter errors and bad inputs account for the majority of problems folks have with balllistic solvers.

Thats the first thing I thought of. I verified the app was set to use a single BC and the G1 function. I Thought it was ironic that the corrected BC was very close to the G7 listed for the 162 eldx. Ive gone over all the data including scope height measurements probably 4 times. Im going to re zero at 100 and see if I can get it squared away. Theoretically i should be able to punch a 100 yard target into my program and dial accordingly. If my POA and POI dont match then that should indicate that the zero was off a little which I'm assuming it most likely is.

 

[Wrench]

Tall target test it at that time amd kill two birds with one stone.