Ballistics Help

[Kyle Wheeler]

I wanted to see if anyone has some suggestions for my 7 mag. I’m shooting factory 162 ELDX and getting right at 3K with a 26 inch barrel. Shooting razor LHT.

The ballistic calculators I’ve tried have been off shooting 8 inches low at 400 and 3-4 inches low at 300. When I true velocity with this in Strelok Pro it says I need to factor in only about 2700 FPS.

I made sure elevation, temp, sight height and all the other variables were correct. I’ve used 4 different calculators to make sure I’m not missing something.. I’ve never had this issue in the past.

Any ideas as to why I would be shooting low consistently?

In the past I shot a 308 and it was always pretty close using the calculators. I just had to sure you velocity.

Thanks!

 

[Outdoorsman12b]

If you have a known velocity then I would double check you have the correct zero range on your calculator and/or your rifle.

if those two things are lined up correctly then it’s probably your shooting form.

 

[Wapiti1]

A few things to think about that could be the issue.

Not knowing your rifle, a slow twist barrel lowers the BC of the bullet. A 1:9.5 will have a lower BC than a 1:8. That can alter the calculation quite a bit. A bullet's BC is either measured using the manufacturer's test rifles, or calculated assuming ideal stability. Your setup will have a different BC. It may be close enough, or it may be quite a bit off. Range data is the only way to verify, then you adjust in your app.

How confident are you in your velocity measurement?

Did you try the new elevation settings the calculator spits out after adjusting the velocity? If they are good, you have the answer. You're marginally stabilized.

Have you shot the box or done any tracking checks with your scope?

Parallax adjusted properly?

Jeremy

 

[MT257]

I've never had much luck with the calculators. I've always found just going out and verifying at the range is best.

 

[Kyle Wheeler]

If you have a known velocity then I would double check you have the correct zero range on your calculator and/or your rifle.

if those two things are lined up correctly then it’s probably your shooting form.

Thank you! Rifle is zeroed well and calculator. Ill continue working on form but in the past haven’t had this issue and it was consistent up and down to 400.

 

[Kyle Wheeler]

A few things to think about that could be the issue.

Not knowing your rifle, a slow twist barrel lowers the BC of the bullet. A 1:9.5 will have a lower BC than a 1:8. That can alter the calculation quite a bit. A bullet's BC is either measured using the manufacturer's test rifles, or calculated assuming ideal stability. Your setup will have a different BC. It may be close enough, or it may be quite a bit off. Range data is the only way to verify, then you adjust in your app.

How confident are you in your velocity measurement?

Did you try the new elevation settings the calculator spits out after adjusting the velocity? If they are good, you have the answer. You're marginally stabilized.

Have you shot the box or done any tracking checks with your scope?

Parallax adjusted properly?

Jeremy

Never thought of the BC. My 7 mag is twisted slower at 1:9.5. I do have this factored in Strelok Pro but not sure if it corrects BC. The berger calculator said I was stable with the 162 ELDX at 3K elevation.

Would I just adjust BC until it matches up with the range results?

I feel good about the velocity. Box says 2940 and my Magnetto speed was getting about 3010 average with a 26 inch barrel.

Can you clarify the new elevation settings?

I’m going to do a box test with scope here soon. From what I’ve seen the LHT should track well. I did set parallax each time. We did have a good amount of mirage but if I’m thinking correctly that would make me shoot higher I believe.

I really appreciate your help!

 

[Kyle Wheeler]

I've never had much luck with the calculators. I've always found just going out and verifying at the range is best.

Nothing beats real world data.

 

[Kyle Wheeler]

This paper target was at 300 yards and 3 MOA. We were just shooting dead center and wind was about 2-3 inches of drift. The drop was 3.5 inches here in the photo. We then corrected and shot steel with 3.75 MOA instead of 3 and here are results on the steel. It was spot on. Same results at 200 and 400 we were shooting low based on what calculator said.

 

[BRTreedogs]

The calculators just do the math for you.
Math is constant.

You must be inputting something incorrectly.

 

[Kyle Wheeler]

It's not BC, LOL. Don't touch BC at 400 yards. While we're at it, it's not spin drift or aerodynamic jump, it's not coriolis, or carbon ring, etc.

For a 1:9.25 twist, and at 3010 fps (assuming Altitude is 0-ft and temp of 70 degrees, the 162 ELDX is 'marginally' stable and BC is compromised by 2% (meaning nothing at your range).

View attachment 304616

It's extremely unlikely that this is due to parallax...even if you have the 50mm version, parallax needs to be at about 43 yards when shooting 400 yards AND you have to have the worst possible head position to get 8" of error at 400 yards. You'd have to really try for parallax to be the problem.
View attachment 304617

At these close distances, probably the biggest issues, and in no particular order:

1. Bad Range
2. Shooter error
3. Bad zero
4. scope/mount/rifle issue

Making a few assumptions of your shooting conditions, the differences in drop between 400 yards and 437 yards (difference in yards to meters) is about 7-inches. The difference in drop from 300 yards to 328 yards (difference in yards to meters) is about 3 inches. Check your rangefinder to make sure it's in yards, put new batteries in it and check it against a known range.

If that's not the issue, post a few of your 100-yard zero groups. Check torques, clean, etc., etc., etc. Static mount the scope and check tracking.

Wow thank you! That amount of drop leads me to believe it could be rangefinder and a slightly low zero. I use the Sig Kilo 1800 and this is the first time I’ve used it. I used to use the razor 4000. Im going to test it with a friends rangefinder next time we shoot.

What about line of sight vs angle compensation? I realized I had it in ABU mode which is line of sight but my angle was set at zero in Strelok. We were shooting in a cotton field so it’s pretty flat. Do you think that would impact it enough?

The groups were consistent and we worked up and down and it was same results so if it was shooter error it was the same error every time.

Here is a picture of my 100 yard zero. We bumped up 1 MOA after this. This was 4 shot group.

 

[Kyle Wheeler]

The calculators just do the math for you.
Math is constant.

You must be inputting something incorrectly.

I agree I’m scratching my head!

 

[762 ULTRAMAGA]

I agree I’m scratching my head!

Do a tall target test asap
My money is on your scope not tracking, I've seen this with quite a few of the cheaper scopes i.e vx5hd, vx6, zeiss v4 and v6.
Hang a chalkline from the top of target and snap a vertical line, make a mark at 10, 20, and 30 moa.
Verify your 100 yard zero and start your test, I like to fire 2 shots every adjustment working up to 30 then incrementally back to zero.
This test can be very eye opening

 

[204guy]

Maybe I missed it but how are you correcting elevation. Dialing, bdc? It's not your solver unless you have an input way off. It's likely your scope or meters/yards as said above.

 

[MTElkChaser]

Do a tall target test asap
My money is on your scope not tracking, I've seen this with quite a few of the cheaper scopes i.e vx5hd, vx6, zeiss v4 and v6.
Hang a chalkline from the top of target and snap a vertical line, make a mark at 10, 20, and 30 moa.
Verify your 100 yard zero and start your test, I like to fire 2 shots every adjustment working up to 30 then incrementally back to zero.
This test can be very eye opening

Agree. And this is pretty easy to do as well. A plumb line or large (4ft or longer) level to draw a plumb line for tracking.

 

[wind gypsy]

Rangefinder ranging in meters and ballistic app in yards seems most plausible.

 

[Kyle Wheeler]

The difference between meters and yards jumps out at me just because it's matching your discrepancy almost exactly. You might go buy a $50 350-ft cloth tape and mark out 400-yards next time you shoot. Obviously a $50 tape isn't a precision measuring tool, but it will definitely pick-up a large error like meters vs yards.

Horizontal range to line-of-sight can cause errors, but not this large when shooting a mostly flat range. An over simplification is that gravity works along the equivalent horizontal range, and wind works along the line of sight range. You'd need about a 25-degree angle for a line-of-sight distance of 438 yards to have an equivalent range of 400-yards.

One other thing about rangefinders is that the Sigs seem to have a fairly generous aiming circle. You should check it out to see where the laser is relative to the aiming circle. A pretty common method is to aim at the top of a power pole until you know where the laser is within the aiming circle.

I have rifle/ammo/scope set-ups that I could confidently zero with 3 or 4 rounds, and I've posted aggregate 20+ shot groups showing why. Not knowing you or your gear, and since you're having problems, use a larger round count to zero.

Also, buy a notebook and log shots, conditions, ranges, etc.

I may try the tape idea. My rangefinder shows yards when I turned it on today but who knows maybe I had it on meters.

I’ll give it another go here in about a week and will zero again and make sure the distance is correct. I’ll turn do a tracking test. There was consistency across all the groups which was encouraging it was just the drop that was off.

I will report back here and again thanks for all the help I really appreciate it as this is my main rig now. I’ve always got my 308 as backup if needed.

 

[Kyle Wheeler]

Do a tall target test asap
My money is on your scope not tracking, I've seen this with quite a few of the cheaper scopes i.e vx5hd, vx6, zeiss v4 and v6.
Hang a chalkline from the top of target and snap a vertical line, make a mark at 10, 20, and 30 moa.
Verify your 100 yard zero and start your test, I like to fire 2 shots every adjustment working up to 30 then incrementally back to zero.
This test can be very eye opening

I sure will! Thank you. I would be disappointed if it wasn’t tracking but we will see! I’ll report back once I get to the bottom of this.

 

[Kyle Wheeler]

Agree. And this is pretty easy to do as well. A plumb line or large (4ft or longer) level to draw a plumb line for tracking.

I sure will! Thanks so much!

 

[Kyle Wheeler]

Rangefinder ranging in meters and ballistic app in yards seems most plausible.

My rangefinder showed yards when I turned on today but I wasn’t checking it when I was shooting so next time i shoot I’m going to make 100% sure but I agree it seems like I was ranging about 30-40 feet more than I should have.

 

[Cahunter805]

Wow thank you! That amount of drop leads me to believe it could be rangefinder and a slightly low zero. I use the Sig Kilo 1800 and this is the first time I’ve used it. I used to use the razor 4000. Im going to test it with a friends rangefinder next time we shoot.

What about line of sight vs angle compensation? I realized I had it in ABU mode which is line of sight but my angle was set at zero in Strelok. We were shooting in a cotton field so it’s pretty flat. Do you think that would impact it enough?

The groups were consistent and we worked up and down and it was same results so if it was shooter error it was the same error every time.

Here is a picture of my 100 yard zero. We bumped up 1 MOA after this. This was 4 shot group.

After you moved up 1 MOA did you shoot a group to check your 100 yard zero?