Scope ap off

[Truc]

This has me a bit baffled,
yesterday I shot steel targets from 550-1025 yards. I'm shooting a 300 SAUM with 200gr 20X bullets at 2830fps. At 550 yards I was .3 Mils high and had to adjust by subtracting .3 mils all the way out to 1000 yards. Once I made the initial adjustments I was making contact up close and at 1000 yards on first shots. 4 first shot hits at 550 and when I went to 950yards plus I hit the first three with the first shot so I'm confident it's right.
I'm trying to figure out where the error might be. My ES is below 5.
Any thoughts would be appreciated

 

[BallisticsGuy]

Well you're probably expecting that the math is a calculation based purely on physical laws rather than an estimation based on a model which includes some physical law but also a ton of parameterized values and a few wild estimations and rules of thumb. It ain't like that. External ballistics is done with a model. There can and will be variances.

Ballistics apps will easily show .2mil @ 1000yrds variance between apps which usually comes down to how the mathematical model is implemented. Then there's your group size so add another .2mil. Then there's air temperature differences which can easily add or subtract .2mil @1000yrds for differences as small as 20deg F. Now add in the wind which can make your bullet travel a longer distance than the straight linear point to point distance which can easily add in a couple tenths of a mil. Now also add in the old lights up sights up kind of optical effects that can really mess a guy up. Oh yeah, don't forget that BC is a function of velocity and a given BC is only accurate within a very narrow window distance from a given MV and the fact that BC's can vary marginally between projectiles and then you gotta add in the slop value for the nut behind the wheel.

You're just expecting too much from something that's not meant to have that much expected of it.

Now specific to your actual case, having .3mil too much at 550 suggests to me that your zero is off or one of your other inputs is off, perhaps click value. If it were click value I'd expect to see the error increase with distance though so I'd start with your zero distance precision.

I did some tinkering in my own ballistics app that I publish and I find that if you get your scope height wrong by 1/2" then you're looking at .2mil difference. Having your zero distance off by just 10yrds (you probably wouldn't be able to see this) would easily toss in another click. So, look at your inputs. DM me if you need help.

 

[Truc]

I appreciate your thoughts, yes my scope height was off by .4" and that did make a .1 mil. difference on my setup. I will have to double check my zero. I did notice a guy that was shooting yesterday that also had issues. He was using the same dope that he did on Friday and struggled getting it to go where he was expecting it. He was constantly shooting just over the target, so I'm guessing this is the external ballistics you were referring to?

 

[JungleShooter]

I did some tinkering in my own ballistics app that I publish and I find that.....

I would love to try it out, BallisticsGuy!
Got a link for me?

Thanks!

Matthias

 

[ShtrRdy]

Having to subtract 0.3 mil off for each distance sure sounds like the zero is off.

Could the zero setting in the ballistic program be different than the distance you are zeroing the weapon system?

Are you shooting from a different position/rest when shooting out to distance compared to shoot to zero?

 

[Truc]

Now that you mentioned it, I did use a different rear bag. Yesterday started out frustrating as ….
while I've been shooting this match for several years I switched guns and just couldn't get comfortable with my setup. Different stock, bipod, and cartridge.
I was sure my zero was set before I went, but then my horizontal was .5 mil off also. Rear bag could be the issue, thanks

 

[emp1953]

At ranges beyond 500yds spin drift can come into play, more so with some bullet rifle combinations than with others. Scope cant is also a hiding gremlin that will give you fits. The only way I found to combat scope cant is with a level. I have one that is integrated into the top of my rear scope ring( Nightforce level ), easy to glance at as I settle into position. This model works best on my hunting rifles. I never realized how crooked I can hold my rifle until I started using that, keeps me honest every time.

 

[JungleShooter]

A level has been keeping me on the level as well.

However, mounting the level is only accurate if the gun's rail is perfectly installed in relation to the barrel....
Installing the level on the scope tube itself avoids any imperfection of the gun rail/ barrel.


A failsafe method is to first install the scope so that the vertical crosshair intersects with the center of the bore.
(You can aim at a mirror and turn the scope in the loosened rings until the vertical crosshair is in the middle of the barrel)
This first step will avoid scope cant.


A second step is then to install a level on the scope tube.
Aim the gun at a plumb line and rotate it so that the vertical crosshair is parallel to the plumb line.
Now (while keeping the gun in this position) rotate the level until it shows perfectly level, and tighten it down.
This second step will avoid gun cant.


Matthias

 

[BallisticsGuy]

At ranges beyond 500yds spin drift can come into play, more so with some bullet rifle combinations than with others. Scope cant is also a hiding gremlin that will give you fits. The only way I found to combat scope cant is with a level. I have one that is integrated into the top of my rear scope ring( Nightforce level ), easy to glance at as I settle into position. This model works best on my hunting

This is also important. It will result in hitting off to one side and low.

I appreciate your thoughts, yes my scope height was off by .4" and that did make a .1 mil. difference on my setup. I will have to double check my zero. I did notice a guy that was shooting yesterday that also had issues. He was using the same dope that he did on Friday and struggled getting it to go where he was expecting it. He was constantly shooting just over the target, so I'm guessing this is the external ballistics you were referring to?

It's hard to tell without much more info. 500m isn't far so you need pretty serious errors in inputs to get a difference that'll make someone shoot over the target completely. I suspect that he has multiple issues including shooter skill and rest surface changes apart from inputs errors and gun setup issues as possible contributors.

I would love to try it out, BallisticsGuy!
Got a link for me?

Thanks!

Matthias

ballisticxlr.com click products, downloads, select BallisticXLR v10.5. All downloads are free, support is free. LMK if you need help with the inputs. The other downloads include some that are experimental. Only BallisticXLR is to be considered 100% mature. BallisticPRS is not considered mature. The other calculators are pretty mature.

Now that you mentioned it, I did use a different rear bag. Yesterday started out frustrating as ….
while I've been shooting this match for several years I switched guns and just couldn't get comfortable with my setup. Different stock, bipod, and cartridge.
I was sure my zero was set before I went, but then my horizontal was .5 mil off also. Rear bag could be the issue, thanks

Changing the surface you shoot from, the support you use, etc... can be contributors. Getting everything set up just right and your inputs just right can be challenging and then once you go get it nailed, you have to compare apples to apples to see what kind of difference in POI you get from things like shooting off a bipod on concrete vs. dirt vs. off of bags, etc...

 

[emp1953]

This is also important. It will result in hitting off to one side and low.


It's hard to tell without much more info. 500m isn't far so you need pretty serious errors in inputs to get a difference that'll make someone shoot over the target completely. I suspect that he has multiple issues including shooter skill and rest surface changes apart from inputs errors and gun setup issues as possible contributors.


ballisticxlr.com click products, downloads, select BallisticXLR v10.5. All downloads are free, support is free. LMK if you need help with the inputs. The other downloads include some that are experimental. Only BallisticXLR is to be considered 100% mature. BallisticPRS is not considered mature. The other calculators are pretty mature.


Changing the surface you shoot from, the support you use, etc... can be contributors. Getting everything set up just right and your inputs just right can be challenging and then once you go get it nailed, you have to compare apples to apples to see what kind of difference in POI you get from things like shooting off a bipod on concrete vs. dirt vs. off of bags, etc...

I've seen guys using magnetospeed chronographs get significant changes in point of impact when using the chrony.

 

[BKM]

There are many things that can alter ur dial up from day to day.
First of all u have to have a good zero. Next ,all the data entered into ur app has to be correct. The thing that many shooters get wrong is their velocity or bc. Just because ur chrono , lab radar or magneto speed gives u a number doesn't mean it's correct.
If u are familiar with truing then true ur velocity preferably at 500, 1000, and farther if u can after u verify ur zero. Some bullet manufacturers inflate their bc's also. Check in Litz's library to see if he has put a bc on ur particular bullet. If he has go with it.
Once u have the correct bc and velocity things should come together nicely. Don't forget to input the correct temp, humidity and barometric pressure. A kestrel is a necessity. If ur using data from a nearby weather station it may or may not be spot on for ur location. The last thing is uneven terrain.
If the wind is blowing over humps and valleys u can have vertical dispersions as well. Hope this helps.

 

[emp1953]

Having to subtract 0.3 mil off for each distance sure sounds like the zero is off.

Could the zero setting in the ballistic program be different than the distance you are zeroing the weapon system?

Are you shooting from a different position/rest when shooting out to distance compared to shoot to zero?

Could using meters instead of yards account for this needed correction.