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

What bullet are you shooting and have you chronographed the current ammunition you are using?

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Fed factory 107 SMK
And yes all current for lot number.
I have had this issue for a couple weeks.

I thought adjusting true velocity would give me the correction, but it did not.


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List your details and someone will run the numbers for you in a different program

I’m going to take the initial advice and check 0 again. Then shoot a larger sample for velocity, and try to get a better angle on the wind.

Yesterday the wind was 1-2 mph to my back so couldn’t have caused me to be 1/2 minute low.

I’m also going to put a group of 5 on paper at 300 and then come back to the experts with complete information.


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Fed factory 107 SMK
And yes all current for lot number.
I have had this issue for a couple weeks.

I thought adjusting true velocity would give me the correction, but it did not.


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Can you clarify—I may have misunderstood but I’d thought you said you were using a chrono’d velocity from a different gun. Did you chrono that lot of ammo in that specific gun? If not, thats what you need, the same ammo will have different velocity between different guns.
Then double check all your app inputs and follow post #2. You can then true BC to line up with your actual dope.

0.5moa is also almost certainly within the cone of your rifle. You may simply be seeing an artifact of a small number of shots. If your zero is off by even 1 click as a result
of adjusting off only 3 shot groups, then when combined with small groups, even with an exceptionally precise rifle that can easily show up as an apparent 0.5moa error. Plus you need to know the size cone you are shooting to say whether any shot is inside it or not. So for certain you need to shoot at least 10-round groups (if not larger) for some of this initial setup.
 
Can you clarify—I may have misunderstood but I’d thought you said you were using a chrono’d velocity from a different gun. Did you chrono that lot of ammo in that specific gun? If not, thats what you need, the same ammo will have different velocity between different guns.
Then double check all your app inputs and follow post #2. You can then true BC to line up with your actual dope.

0.5moa is also almost certainly within the cone of your rifle. You may simply be seeing an artifact of a small number of shots. If your zero is off by even 1 click as a result
of adjusting off only 3 shot groups, then when combined with small groups, even with an exceptionally precise rifle that can easily show up as an apparent 0.5moa error. Plus you need to know the size cone you are shooting to say whether any shot is inside it or not. So for certain you need to shoot at least 10-round groups (if not larger) for some of this initial setup.

Same lot shells, same rifle, chronographed in same area on same day.

I think the rifle really wants to be .5 MOA at 500 yards, and I need to check the me variable first with larger samples on all fronts.
Will report back…


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Sometimes it appears to me that a ballistic app is just to get you close. I don’t think I’ve ever NOT had to adjust from what the 4DOF app says to get on target shooting factory.223s at 3 and 4 “ gongs at 500 yards. So many variables!
 
I think the rifle really wants to be .5 MOA at 500 yards, and I need to check the me variable first with larger samples on all fronts.
Will report back…
That would be great, but ime unlikely. This is quite possibly the issue. In some ways its an issue of expectation—the shots will disperse from average point of impact into a bell curve with MOST shots falling relatively close to center, but a predictable and significant portion of them will land 2 and 3 standard deviations outside that “core” group—thats all BEFORE any human error. So any random 3 or 5 shot group is relatively likely to not have one of those “ 3sd’s outside the core” shots so it’ll look “better”, but may very well still be well off true center of cone. Its a very, very rare rifle that actually has a .5moa cone. So if you are shooting 3-shot groups and often getting .5moa results, as soon as you go to a 10+ round group you will see that double or triple in size. Thats not human error, thats just how it works. The key is that unless you have an uber-precise rifle (which ime isnt common even with a full custom), its going to wind up as a 1.2 or 1.5moa group, and any one 3-shot group could be centered well off from the actual center of the bigger group—easily more than a scope-click off.

Basically you need to somehow account for the 32% of your data (ie impacts) that fall outside of 1 standard deviation away from the true average point of impact. This alone could realistically, and commonly does, account for the amount of error you are seeing at 500Yds. Could easily be velocity is slightly off, bc almost certainly needs trued, scope tracking may be off…but ime this factor is usually at least a significant contributor to the issue, both in zeroing as well as in reading the impacts at distance vs expected impact, those two things being ADDATIVE. (Ie any error away from expected poi caused by measuring from a small group at distance, is on top of zeroing error caused by same)

IMG_5055.jpeg
 
Update
Downloaded AB Quantum

Input data, and initial output is correct to my current dope at 485 at 8.9’ up. This is true to my field adjustment of 9’ to hit center of plate.

I’ll follow up the next time I shoot, but it looks like the Hornady App is just wrong on this bullet.


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You're talking about a 2 and a half inch difference in POA and POI at 484. Was all of the prediction error in the vertical, or was the horizontal growing or drifting also. I wouldn't fix anything UNTIL.....

I verified my scopes tracking correction factor on a tall target.

I shot beyond 484 by a couple hundred yards to see if I had a consistent change in trajectory OR....was I shooting across a terrain feature that was inducing unseen correction factor. I'd also question how you set parallax and how your understanding of it affects impacts.....and how does your rifle mechanics change between the two distances in question.

I need to trim a little time out of a vid I did last week when validating BC at 1140 and in that I am calling the velocity and have two shots land within a couple of inches even though there's a 25fps spread.....so is it chronograph error, my form error working in my favor or just random luck of shots falling in my favor.....probably all the above.

Moral of the story is you need another data input at a longer range to help understand whats going on where you are now.....OR

If 484 is as far as you have to shoot, true for that to be nearly perfect and backwards validate your corrections and split the velocity to make it work.....BUT understand that you will only be effective at that distance and within THAT DA figure.
 
Shoot a 20 or even better, 30 shot group to check zero. Shoot as many as you can before mirage starts to get bad then back off and let it cool before you continue.

I think the problem here is that if youre off at 300yds, its just off, thats not truing. Im willing to bet your velocity is off. Height over bore and smaller stuff like that isnt going to be as big of a factor for this conversation.

Ideally, you would chrono the large group used to zero on that day and use that data. Plug it in and then go out to a distance where youre comfortable to verify. The further the better, within reason. Adjust your velocity to match your impacts and then verify close up shots again at 300, 400, 500.

I always adjust velocity first and try to stick with that. If it's just not working then I mess with BC.

Ive seen weird shit with the 4dof app but ive also seen it be really close with hornady bullets. I dont use it as my main calculator so I cant say. I use the Sig BDX app which came with my Gen 2 Kilo LRFs. Its based off of AB data. Ive also found their custom drag curves to be much closer than a static BC.

The image below is from a Bryan Litz book but illustrates the BC for the 107smk at different velocities. Just including so you can visualize that BC isnt a static number. Velocity is, within reason, it's more of a constant so adjusting that to true makes more sense.
 

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You're talking about a 2 and a half inch difference in POA and POI at 484. Was all of the prediction error in the vertical, or was the horizontal growing or drifting also. I wouldn't fix anything UNTIL.....

I verified my scopes tracking correction factor on a tall target.

I shot beyond 484 by a couple hundred yards to see if I had a consistent change in trajectory OR....was I shooting across a terrain feature that was inducing unseen correction factor. I'd also question how you set parallax and how your understanding of it affects impacts.....and how does your rifle mechanics change between the two distances in question.

I need to trim a little time out of a vid I did last week when validating BC at 1140 and in that I am calling the velocity and have two shots land within a couple of inches even though there's a 25fps spread.....so is it chronograph error, my form error working in my favor or just random luck of shots falling in my favor.....probably all the above.

Moral of the story is you need another data input at a longer range to help understand whats going on where you are now.....OR

If 484 is as far as you have to shoot, true for that to be nearly perfect and backwards validate your corrections and split the velocity to make it work.....BUT understand that you will only be effective at that distance and within THAT DA figure.

500 is what we have right now.
I will do all those things, but wanted to clarify that the output matches the results with this app, vs was 1/2 minute off before and about 1/3 minute off at 300 yards.

Definitely appreciate all the responses, and will keep coming back until I understand what I’m doing and the bullet.

I am trying to get the rifle dialed in well enough for a 400 plus yard shot on a deer, but not over 500 ever with a 6 CM.
I’m not trying to experiment like that.

I’ll learn with the 6, then move on to the 7 and 300…


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You're talking about a 2 and a half inch difference in POA and POI at 484. Was all of the prediction error in the vertical, or was the horizontal growing or drifting also. I wouldn't fix anything UNTIL.....

I verified my scopes tracking correction factor on a tall target.
This. @B Harrison have you confirmed tracking?
 
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