Need help with 500 yard trueing up calculator on a 6 CM

[B Harrison]

I’m having some trouble making sense of the corrections to the Hornady app.

Seekins PH3
Factory Fed 107 SMK
Have velocity from an old p35
Have actually adjusted the come up (I think) and getting decent hits at 484 yards and at 300…….

I can’t get any listed BC’s to work with what I think is the actual come up at 484.

Everything in the calculation calls for 8.5 MOA, but I’m good at 9.

All other data is very close, hits at 300 are also 1/2 MOA off calculation.

I’m in WNC and still learning to shoot at distance, but the rifle is good, cold bore hits within a 1/4” of the POA and groups with this ammo are 1/2 MOA consistently, so I know any bad shots are not the rifle.


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[Fred@Exterra]

When we are truing up an app to actual data, the first thing we look at is our 100 yard zero- it needs to be absolutely spot on. This usually takes a couple of ten shot groups to get the cone perfectly centered.

The second thing I look at is the scope. Shoot a tall target at zero, then at + 20 MOA & measure the actual distance between them… it should be 20.94” between the two. If it’s not, there is a correction in the app for that type of error.

Next is chronograph error… they are all wrong, some are just wronger . Light screen graphs are notoriously inaccurate, magnetospeeds are better & the new Doppler radar are the best (currently). I wouldn’t be surprised to see 100+ fps correction here.

Lastly, I start tweaking the BC. Ballistic Coefficients are reasonably tricky to measure and vary from rifle to rifle (depending on speed & stability), so seeing some variation isn’t a surprise.

For a long time, it was recommended to true up at close range (~500 yards) using speed, then fine tune at long range with BC.

EDIT: the first, first thing to look at is environment. Is your range flat, is you temperature, pressure & humidity correct for both ranges. Is there the possibility of an updraft or downdraft at your range.


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[Castle Rock]

Simple rule of thumb is to only use the Hornady app with Hornady bullets and even then there are much better options.

 

[B Harrison]

What is a better app? Even if it costs an initial fee.

I’m a beginner at past 300.
I will likely never shoot past 1000 yards, just want to practice and understand so that I am prepared and able.


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[elsb0048]

Far from an expert here I'm a similar experience level to you.
*But* you sould also check your scope to bore offset measurement. if you didn't actually measure it with calipers and shims and eyeballed it with a ruler like I did you could be off a fair bit. That causes wonkiness when truing velocity as well

 

[Fred@Exterra]

What is a better app? Even if it costs an initial fee.

I’m a beginner at past 300.
I will likely never shoot past 1000 yards, just want to practice and understand so that I am prepared and able.


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Shooter is popular & well supported on here. I also like AB Quantum. They all do about the same thing, just with different minor irritants


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[Dave Thomas]

True your velocity first, bc would have to be way off to make a big difference at 500. Fred had good advice above.

 

[Castle Rock]

I prefer Ballistic AE

 

[dårlig jeger]

Do not skip the tall target test mentioned by @Fred@Exterra. We have seen form test scopes with nearly 10% error.

 

[grfox92]

I’m having some trouble making sense of the corrections to the Hornady app.

Seekins PH3
Factory Fed 107 SMK
Have velocity from an old p35
Have actually adjusted the come up (I think) and getting decent hits at 484 yards and at 300…….

I can’t get any listed BC’s to work with what I think is the actual come up at 484.

Everything in the calculation calls for 8.5 MOA, but I’m good at 9.

All other data is very close, hits at 300 are also 1/2 MOA off calculation.

I’m in WNC and still learning to shoot at distance, but the rifle is good, cold bore hits within a 1/4” of the POA and groups with this ammo are 1/2 MOA consistently, so I know any bad shots are not the rifle.


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Are you using a chronograph? What bullet are you shooting?

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[waspocrew]

Did you chrono the ammo through the rifle you're shooting? I know you mentioned:

Factory Fed 107 SMK
Have velocity from an old p35

If you don't have the velocity from your rifle, then you can't expect the generated solution to be correct.

 

[Fred@Exterra]

Far from an expert here I'm a similar experience level to you.
*But* you sould also check your scope to bore offset measurement. if you didn't actually measure it with calipers and shims and eyeballed it with a ruler like I did you could be off a fair bit. That causes wonkiness when truing velocity as well

Especially if you enter it in the “Sight Offset” instead of the “Sight Height” data field… chased my wiener for a whole afternoon one day. I sure felt smart

The easiest way to measure & calculate the “Sight Height” is (1/2 x Scope Objective Housing Diameter) + (1/2 x Barrel Diameter) + (Gap between the barrel & Objective Housing). I take all of these measurements in a line at the front of the scope. Calipers work best, but I’d feel comfortable with careful measurements using a steel rule.


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[ajf243]

Every scope should have some version of a tall target test, either shot at 100 yrds or run off a jig
I have two NF scopes off about 6%.
This put me about a 1/2moa off at 500yards I recall.

If this is happening it will likely lead to fiddling with BCs and velocity to true it up and you'll just chase your tail from there.

 

[Cahunter805]

Lots of good advice given.

What scope is on the rifle?