Range Report Drop chart never seems correct

[chooter]

With known distances and supposed BC's my results are not correct. So I got the bright idea is that the scope rail cant is the cause of the problem. Assuming that the various programs the drop is figured with a 0 degree cant and that I am using a 20 min cant, is that actually where the discrepancy is?

Are there any programs that figure in the cant for the drop chart?

Chime in.... inquiring feeble mind needs to know!

 

[Forward543]

Cant is unlikely the issue. You have most likely entered data wrong, or have a scope that does not track correctly. Go through all the settings in your calculator and make sure atmospherics are entered right as well. If all of these check out, start pursuing a mechanical issue. Do a tall target test and verify velocity on a labradar or magneto speed. Ammunition dispersion is another place to look.

 

[ballistic1]

Your rail being O moa or 20 moa, or whatever, will have no bearing, once you have
your gun zeroed at a starting base range, such as 100 yds.

Your gun will not shoot the bullets any differently regardless of the rail's
built in cant.

All the differing rail cant will do is move your zero point on your scope's
elevation erector.

Your trajectory chart issues downrange are most likely input related on
whatever ballistic solver you are using

 

[_Windrider_]

With known distances and supposed BC's my results are not correct. So I got the bright idea is that the scope rail cant is the cause of the problem. Assuming that the various programs the drop is figured with a 0 degree cant and that I am using a 20 min cant, is that actually where the discrepancy is?

Are there any programs that figure in the cant for the drop chart?

Chime in.... inquiring feeble mind needs to know!

Lots of info here on truing your BC. It’s discussed ad nauseum. I suggest you look through the threads and podcasts on how to do it. But also make sure you have your software set correct.....which calculator are you using?

 

[chooter]

Applied ballistics and or Sierra

 

[b6graham]

How did you get velocity?

 

[chooter]

Oehler chrono

 

[ShtrRdy]

Did you get a good measure of the distance between bore and scope? Probably something around 2"?

 

[chooter]

Yes. Leopold high 34mm rings, 20 min rail.

 

[chooter]

Yes. Leopold high 34mm rings, 20 min rail.

Yes on the measurement.

 

[hafejd30]

My process is

- Get a load that shoots great
- Test on the magneto speed to get velocity
- use that as a basis for my StrelokPro
- sight in at 100- set and record sight in conditions
- After Sighting In I shoot 300/500/800 yards to get actual drop
- Adjust StrelokPro accordingly to account for the drop
- run with those numbers as a baseline

Even with everything done correctly it’s not uncommon to be 1/2 MOA off due to conditions/minor changes in equipment/reloading components etc etc

The only way to get a accurate drop is by putting rounds down the barrel. Nothing else can replace real rounds on target

 

[lash]

As already said, the cant of your rail has zero, none, nada impact on your ballistic trajectory once zeroed. You have to check and double check your input data used in your apps. More than a few times, I’ve addressed this question here and at the range. Most time it has to do with an incorrect entry or no entry in a field that should have one. The easiest way for you or us to review and reject or correct this as the problem is for you to provide screen shots of your data inputs to your ballistic application and you trajectory results on screen.

It’s easy enough to become confused or not understand what is asked for when first using the applications.

Also, you really haven’t provided any specifics with regard to the issues you are experiencing.

 

[b6graham]

As already said, the cat of your tail has zero, none, nada impact on your ballistic trajectory once zeroed. You have to check and double check your input data used in your apps. More than a few times, I’ve addressed this question here and at the range. Most time it has to do with an incorrect entry or no entry in a field that should have one. The easiest way for you or us to review and reject or correct this as the problem is for you to provide screen shots of your data inputs to your ballistic application and you trajectory results on screen.

It’s easy enough to become confused or not understand what is asked for when first using the applications.

Also, you really haven’t provided any specifics with regard to the issues you are experiencing.

A common one when we get to this point is shit angle being confused with bearing

 

[Steel head]

As already said, the cat of your tail has zero, none, nada impact on your ballistic trajectory once zeroed. You have to check and double check your input data used in your apps. More than a few times, I’ve addressed this question here and at the range. Most time it has to do with an incorrect entry or no entry in a field that should have one. The easiest way for you or us to review and reject or correct this as the problem is for you to provide screen shots of your data inputs to your ballistic application and you trajectory results on screen.

It’s easy enough to become confused or not understand what is asked for when first using the applications.

Also, you really haven’t provided any specifics with regard to the issues you are experiencing.

This.
Somewhere your inputting bad data and getting corrupted results

I went from a 20 to 30 moa rail.
After I got my zero my data and drops are exactly as before.

 

[Long Range 338]

attach screenshots of your data entry for us keyboard commandos to constructively criticize....

 

[lash]

attach screenshots of your data entry for us keyboard commandos to constructively criticize....

Lol

 

[wade2big]

Did you get a good measure of the distance between bore and scope? Probably something around 2"?

This actually makes very little difference within reason.

 

[McSnipsy291]

Round down the bc a bit and see if it helps.. anytime someone posts High BCs or sub 1/2minute groups it should always be taken with a grain of salt

 

[Lowlight]

BCs are AVERAGES

Averages determined at 300 yards, which is the shortest possible range you can actually use. BCs are not wrong, just not static, they are dynamic. They are based on Muzzle Velocity, they are affected by a host of things including the powder used, the rifling and then there is Shooter input into the shot.

A computer cannot fix your bad fundamentals, a computer cannot predict when you broke the shot at a weird point in your breathing. A computer cannot fix the cant you induced in your rifle while firing. The Human Factor is Real.

A BC is a starting point where the end user can if one so chooses to true and fine tune the number for their rifle system.

As been noted,

Scope Calibration is the biggest point of error next to shooter induced errors, if you have not tested your scope, you cannot complain about software being off.

Your 100-yard zero has an effect, are you Point of Aim, Point of Impact or is there a small variation in it. See Hornady True Range Zero for more details

The cant in your scope rail is .11" from front to back if you think .11" is the culprit it is probably you.

You cannot align the rifle to the computer, the computer must be trued to what your system is shooting. In other words, you have to collect the shooting data first and put it into the computer after to true it. You cannot simply take the computer and hope your rifle matches it, because it won't. Truing is real and how you go about it matters.

You adjust your Muzzle Velocity 600 yards and in, and you adjust the BC 600 yards and out to fine-tune the program. Depends on your range and how far you are shooting, but you have to know what you are doing.

The bullet maker is not lying, is not making up numbers, it's just those numbers are an average based on a certain set of conditions and a specific rifle system it from fired from. BCs are FLUID they should be adjusted for your system if you want them to be accurate.

 

[lte82]

You could be holding too much Coriolis or dialing too much for aerodynamic deflection based on the parameters of trajectory. Point mass solvers are much more intricate in design and you probably need a custom 6dof program to accurately calculate drop. I spoke to a top PRS shooter that is basically running his own software and developed one weird trick to help maximize the bc to overcome these limitations. Last, how many inches does the back of the box say the drop should be? Those are usually really close.

Kidding. I would re-read Franks advice again, he's spot on. Test your scope, verify velocity, and tweak bc until your dope matches at all distances.

 

[pbatesaz]

A common one when we get to this point is shit angle being confused with bearing

I’m guessing you meant “shot” angle. Otherwise I have to completely re-think this pastime ?

 

[Long Range 338]

You could be holding too much Coriolis or dialing too much for aerodynamic deflection based on the parameters of trajectory. Point mass solvers are much more intricate in design and you probably need a custom 6dof program to accurately calculate drop. I spoke to a top PRS shooter that is basically running his own software and developed one weird trick to help maximize the bc to overcome these limitations. Last, how many inches does the back of the box say the drop should be? Those are usually really close.

Kidding. I would re-read Franks advice again, he's spot on. Test your scope, verify velocity, and tweak bc until your dope matches at all distances.

You had me going there for the first paragraph! I was like WTF? (and not wind, trajectory, fundamentals...)

 

[Greg Langelius *]

Adding to Frank' advice, BC's and Effective BC's can become even more of a variable when we factor in altitudes and/or density altitudes.

The link looks complicated; but in effect, as altitudes increase, the effective BC also increases. This is because air density affects velocity decay, and less density decreases flight time by decreasing effective drag. Consequently, the bullet arrives in less time, with less drop due to acceleration from to gravity. I.e. Get there sooner, drop less.

You say your drops are not correct, but I can't find where it says they are observed to be higher or lower than predicted. When I add significant altitude to my Pejsa calculator, it reports a corrected BC that's significantly higher too.

Another factor to consider is Chrono/muzzle distance. Too close to the muzzle; and it's not measuring bullet velocity, but muzzle blast gas velocity. I put my chrono about 20ft out from the muzzle.

Greg

 

[chooter]

sight in range and match range are virtually same elevation. approx ten feet separation between chrono and muzzle because I chrono and shoot for groups at the same time.

 

[308pirate]

sight in range and match range are virtually same elevation. approx ten feet separation between chrono and muzzle because I chrono and shoot for groups at the same time.

You got your answer from Frank. Now go put it in practice.