Ballistics Question

[elkaholic]

Clamp your scope solidly with it at maximum power aimed and focused at a ruler exactly 50 yards away from the front of the scope and at exact right angles to the line of sight. Make sure the ruler's aligned straight with a reticule wire. Align the reticule on an even inch line. Count the clicks as the reticule moves to another inch line 2 inches away.

If it takes 17 clicks to move the reticule exactly 2 inches at 50 yards, each click's worth .2353 MOA. Check both elevation and windage to verify they're both the same. If 17 clicks don't put the reticule exactly on the ruler 2 inches away, keep moving the adjustment in the same direction until it aligns exactly on an inch line; counting clicks all the way. Then divide the inches moved by the clicks to get there. 1 MOA in the shooting sports is exactly 1/2 inch at 50 yards.

You'll get a bit more accurate results if the ruler's at 100 yards.

Bart.....just used this method on my Sightron SIII 8x32. I set the ruler up at 96 yards as I figured 1 moa would be as close to an inch as you could get at this range. I clicked up 20 moa which measured 21" and calculated my clicks at .262 moa.......Rich

 

[Bart B]

Bart.....just used this method on my Sightron SIII 8x32. I set the ruler up at 96 yards as I figured 1 moa would be as close to an inch as you could get at this range. I clicked up 20 moa which measured 21" and calculated my clicks at .262 moa.......Rich

What one of the three SIII 8x32 versions do you have? I'll do some checking then see what I get. I think you're right. That's almost a 5% error.

 

[elkaholic]

What one of the three SIII 8x32 versions do you have? I'll do some checking then see what I get. I think you're right. That's almost a 5% error.

I have the 56mm with 2 moa reticle and 1/8 moa dot........Rich

 

[Bart B]

I have the 56mm with 2 moa reticle and 1/8 moa dot.

That one's their SIII SS 8-32x56 LR TD as I see it. Here's what I got doing the math with your data:

At 96 yards, one MOA is .9600 inch based on Sightron's info saying 1 MOA is one inch at 100 yards; that scope's 1/4 MOA clicks are supposed to move impact .2500 inch per hundred yards. At 96 yards, it should move impact exactly .2400 inch. .25 times .96 equals .2400.

If you moved your scope's adjustment 20 MOA, the reticule should have moved 19.20 inches at 96 yards. 20 times .96 equals 19.20 inches.

As the reticule moved 21 inches on a 96-yard target with a 20 MOA adjustment, the scope's reticule moved 21.875 MOA. 21 divided by .96 equals 21.875.

It took eighty 1/4 MOA clicks to move your scope 21 inches at 96 yards. That's .2625 inch per click. 21 inches divided by 80 equals .2625 inch; the number you came up with.

With one click supposed to move .2400 inch at 96 yards but actually moved .2625 inch, that's a +9.375% error. .2625 divided by .2400 equals 1.09375.

At 100 yards, the adjustments would move about .2734 inch per click.

1/4 of an angular (trig) MOA's equal to 0.25133 inch at 96 yards. If your scope's adjustments were spec'd in angular MOA's, it would have only a +4.445% error.

I would be interesting to find out what Sightron has to say about this.

 

[elkaholic]

That one's their SIII SS 8-32x56 LR TD as I see it. Here's what I got doing the math with your data:

At 96 yards, one MOA is .9600 inch based on Sightron's info saying 1 MOA is one inch at 100 yards; that scope's 1/4 MOA clicks are supposed to move impact .2500 inch per hundred yards. At 96 yards, it should move impact exactly .2400 inch. .25 times .96 equals .2400.

If you moved your scope's adjustment 20 MOA, the reticule should have moved 19.20 inches at 96 yards. 20 times .96 equals 19.20 inches.

As the reticule moved 21 inches on a 96-yard target with a 20 MOA adjustment, the scope's reticule moved 21.875 MOA. 21 divided by .96 equals 21.875.

It took eighty 1/4 MOA clicks to move your scope 21 inches at 96 yards. That's .2625 inch per click. 21 inches divided by 80 equals .2625 inch; the number you came up with.

With one click supposed to move .2400 inch at 96 yards but actually moved .2625 inch, that's a +9.375% error. .2625 divided by .2400 equals 1.09375.

At 100 yards, the adjustments would move about .2734 inch per click.

1/4 of an angular (trig) MOA's equal to 0.25133 inch at 96 yards. If your scope's adjustments were spec'd in angular MOA's, it would have only a +4.445% error.

I would be interesting to find out what Sightron has to say about this.

I called Sightron this A.M. and spoke with the technician. He said to send it in and they would check it out. He agreed that this was a pretty healthy error and it is possible to re calibrate it if there was no mechanical flaw, in which case they would repair it.....Rich

 

[elkaholic]

I called Sightron this A.M. and spoke with the technician. He said to send it in and they would check it out. He agreed that this was a pretty healthy error and it is possible to re calibrate it if there was no mechanical flaw, in which case they would repair it.....Rich

I just called Sightron back and they confirmed that it was calibrated in angular moa. Since by definition, moa is a measurement of angle, what is the difference between angular moa and moa?..........

 

[Bart B]

I just called Sightron back and they confirmed that it was calibrated in angular moa. Since by definition, moa is a measurement of angle, what is the difference between angular moa and moa?..........

The difference:

Angular MOA typically means 1.0472 inch per hundred yards. It's based on what the sine of 1/60th of a degree subtends at 100 yards.

MOA typically meant, in the shooting sports for over a hundred years, means 1 inch per hundred yards. Nowadays, it is sometimes stated as inches per hundred yards or IPHY. Scopes calibrated for this typically have their specs written to say 1/8" or 1/4" per click.

Here's some quotes from Sightron's web site for their scope you have:

Click Value 1/4 MOA

Windage and Elevation Movement Table
Click Value 50 Yards 100 Yards 200 Yards 300 Yards
1/8 Minute 1/16"........ 1/8"........ 1/4"....... 3/8"
1/4 Minute 1/8".......... 1/4"........ 1/2"....... 3/4"

If Sightron claims that scope's calibrated for angular MOA, ask them why their online specs and manuals don't state that, but instead state it's calibrated for inches per hundred yards.

The only way they could possibly "recalibrate" it is to replace all the lenses in the scope such that they end up exactly with design specs for them. I don't think they'll machine two new sets of adjustment hardware just for your scope. If that's what's done, I'd be very interested in what another test would show.

Some years ago, Nightforce sent me two of their high end scopes to check for range focus and adjustment accuracy on my optical bench collimator. With both objective lenses set for infinity, one focused at 225 yards with adjustments about 4% off perfect and the other focused at 175 yards with about 6% adjustment error.

If one expects precision adjustments in their rifle scope, they better find out if their scope really has it.

 

[Mikecr]

I disagree.
Minute of Angle, is an exact value. Therefore anything not an exact increment of MOA -is not MOA.
It is the same with MILs, and nobody should be running around describing some sort of 'shooter's MILs'.
Anything can be expressed in Inches per Hundred Yards though. So if adjustments are not another REAL term(like MOA or MILs) you still have IPHY.

It is always amazing how shooters generalize things, even when there is no reason to.
That scope makers also do it must be taken as an insult. i.e. they think we're stupid...
Again, even when they don't have to!

The tech at Sightron was lying to you. Your scope is as close to MOA as it's going to get.
You were smart in testing to find your adjustment value. And now you know EXACTLY what to use in ballistic software.
Problem solved. Good job.

 

[Bart B]

Minute of Angle, is an exact value. Therefore anything not an exact increment of MOA -is not MOA.

It is the same with MILs, and nobody should be running around describing some sort of 'shooter's MILs'.

Mike, I well understand your position in this matter. It may not matter that thousands (millions?) think as I do. Meanwhile, I and all those others will use MOA in the US of A shooting sports to mean one (1.00000000000000000000000000000.... adinfinitum) inch for every hundred yards. That's an exact value, too, and a lot more exact than MOA when the sine of 1 minute of arc is 0.00029088820456342459637429741574..... (there's not enough memory in our computer systems to hold all the digits) nor is there enough in any one of our computers to hold all the digits for the reciprocal of 60 to get a reading more accurate than the sine number above.

Does it matter that there's four different standards around the world for mils? Some are exact values but one is not. The "real" trigonometric unit of an angular mil in use by some telescopic sight manufacturers is based on pi which is not an exact number but starts out at 3.1415926535897932384626433832795...... then goes on and on adinfinitum.

How about the measurements for mile, ton, ounce which have more than one standard. Each unit is an exact value, too.

 

[Bart B]

The tech at Sightron was lying to you. Your scope is as close to MOA as it's going to get.

Without knowing what Sightron's tech understands about scope adjustments, it's not fair to say he was lying. That infers you know he knows all the technical details of scope adjustments and optical specs but intentionally said something he knows is not true. For all I know, he may be ignorant about all of this and just replied as his job requirements called for. I don't think you've any real knowledge of exactly what he does and does not know about scope adjustments. . . .unless you've been (or hired someone to do so) directly monitoring him in his professional environment.

There is a way to get that scope closer to the inches per hundred yards as stated in its specs. The easiest way to change how much one click changes the scope's axis is to replace all the optics forming the target image in the adjustment plane. Lens makers have tools to easily measure a lens' focal length to extreme accuracy. Longer focal lengths make the image larger and that makes the adjustment move less per click across a given point on the target. Shorter total focal lengths make that image smaller and the reticule moves further across a given point on the target per click. Same thing happens with field of view through a given hole size in the scope; high magnifications with longer focal lengths reduce the field of view; low magnifications with shorter focal lengths increase the field of view. We don't know if Sightron will do this, but they could.

 

[elkaholic]

Without knowing what Sightron's tech understands about scope adjustments, it's not fair to say he was lying. That infers you know he knows all the technical details of scope adjustments and optical specs but intentionally said something he knows is not true. For all I know, he may be ignorant about all of this and just replied as his job requirements called for. I don't think you've any real knowledge of exactly what he does and does not know about scope adjustments. . . .unless you've been (or hired someone to do so) directly monitoring him in his professional environment.

There is a way to get that scope closer to the inches per hundred yards as stated in its specs. The easiest way to change how much one click changes the scope's axis is to replace all the optics forming the target image in the adjustment plane. Lens makers have tools to easily measure a lens' focal length to extreme accuracy. Longer focal lengths make the image larger and that makes the adjustment move less per click across a given point on the target. Shorter total focal lengths make that image smaller and the reticule moves further across a given point on the target per click. Same thing happens with field of view through a given hole size in the scope; high magnifications with longer focal lengths reduce the field of view; low magnifications with shorter focal lengths increase the field of view. We don't know if Sightron will do this, but they could.

Actually, when I asked the question to the tech, his answer was "I don't know, I will go ask the Wizard" or whoever the head tech was? He returned a couple of minutes later and said "yes, it is angular". I guess I'm not sure at this point whether to send it in as he said, or just live with the correction.......Rich

 

[Mikecr]

It may not matter that thousands (millions?) think as I do. Meanwhile, I and all those others will use MOA in the US of A shooting sports to mean one (1.00000000000000000000000000000.... adinfinitum) inch for every hundred yards.

What do you think it REALLY says about thousands(millions) of Americans then?
It merely implies to me that we readily accept delusions, when easier.

But this is a long range hunting site, and shooters here(hundreds) should strive to know and use the difference between MOA and IPHY.
It's not rocket science, folklore, or pseudo-facts, and it matters in the field.

Do YOU accept that MOA is NOT 1.00 inch per 100yds?

 

[JOSE A. MARINE]

so after all this testing, what do you adjust, mv or bc? I have EXBAL, and dont always get "real close".

I´ve worked with several programs, and EXBAL is about the closest I can get to real life, but I have always lived with some degree of inacurracy...maybe my shooting..haha.

I have shot bullets across four different chronos at the same time and found different velocities between them, sometimes 15% off from one to the other...so I always move -MV first, then BC.. but as above, always lived with some degree of inacurracy....

which is most practical...? MV or BC?

JOSE

 

[barnesuser28]

first i would verify how much your crosshairs move per click and that should fix your inaccuracy