UltraDot ?

[rifal]

Could someone tell me what the standard sight correction (clicks) is on an ultradot scope when going from 50 Ft. to 25 yds. Caliber is .22 LR.

Thanks

Don

[GOVTMODEL]

Zero clicks.

[rifal]

That was easy.

Thank you

Don

[Jaybar]

Zero adjustment may or may not be valid. It depends on the height of your UltraDot above the bore and/or the ammo you use. I had one gun a few years ago (High Standard) with the dot mounted fairly high above the bore. When sighted in at 25 yds with Remington Target, the POI at 50 yds was about 3/4" high. If I used RWS Target with the same setup there was no adjustment needed between the short line and the long line. The lower your Dot is in relation to the bore, the less likely that you'll need any adjustment between the lines.

[Guest]

With my GSP and Ultra Dot Match Dot (using CCI SV ammo), the adjustment to go from 50 ft to 25 yds is 4 clicks down (i.e., the bullet is still rising to the line of sight at a 50 ft zero). One of my team mates with the same setup uses the same 4-click adjustment.

[Ed Hall]

The lower your Dot is in relation to the bore, the less likely that you'll need any adjustment between the lines.

Although the rest of the post is correct, the quote above is not true.

The bullet is in an accelerated fall (trajectory) from the centerline of the bore as soon as it leaves the muzzle. To have zero adjustment at two distant points, you have to have those points coincide with the rise and fall of the bullet as it crosses the sight line.

All bores are angled upward in relation to the sight line. The bullet leaves at an upward angle, crossing the sight line, reaches its apogee and then falls, crossing the sight line again. The closer the sight line is to the center line of the bore, the sooner the first crossover is (closer to the muzzle). Note that you could have only one point if you adjust the sight line to coincide with the apogee of the trajectory with the sight line level.

As Jaybar correctly mentioned, the variances depend on the speed of the bullet and the height above the bore. For my 208s, my zero is pretty close at both 25 and 50 yards with the scope more than an inch above the bore, firing standard velocity ammo. 50 feet and 25 yards (75 feet) are normally close enough to leave alone. If the first crossover is at 25 yards, with the scope one inch above the bore center line, the impact should be less than one-third inch lower at 50 feet (two-thirds of 25 yards). Note the impact would be lower at 50 feet, demonstrating why "Guest" with his GSP moves his sight down when going to 25 yards.

Take Care,
Ed Hall
U.S. Air Force Competitive Shooting Teams
Bullseye (and International) Competition Things

[Spencer]

All bores are angled upward in relation to the sight line.

Without bore sighting one of my .22s I hesitate to say what is the case for rimfires, but for CF many appear to have sights that angle down from the sight line (to allow for recoil that occurs before the bullet leaves the barrel). This is particularly noticable for the shorter barreled big calibre pistols.

Spencer

[Ed Hall]

Very good point, Spencer.

I think you meant to write:

"...but for CF many appear to have bores that angle down from the sight line..."

And, my statement should have been:

"All bores are angled upward in relation to the sight line at the moment the bullet exits the muzzle."

-----------------------------------------------------------

Now on to something a little different, but quite interesting to me:

In doing some math for this addendum, I stumbled across something that seems too simple to be correct, yet appears to calculate out. I invite all the mathematicians to jump in and dispute or validate my findings.

The apparent discovery:

It appears that the ideal distance between the bore center line and the sight line to allow for the same zero at 25 and 50 yards, is one-half the amount of bullet drop at 50 yards. This is speaking mathematically without regard to air friction, which of course is considerable.

Let's step through an example. All are invited to follow my calculations:

Let's choose 1070 fps for our bullet velocity (because it lends to easy rounding at 50 and 25 yards).

Drop due to gravity is equal to (about) .5 times 32.17 times time times time times 12. The result will be in inches.

My calculator shows the following for the transit times for 50 and 25 yards (150 and 75 feet, respectively):

150 feet at 1070 fps = 0.14018691588785 and a few more places.
Let's round to 0.14 second.

75 feet at 1040 fps = 0.07009345792523 and some more digits.
Let's round to 0.07 second.

Now, let's calculate the bullet drop:

150 feet = .5 * 32.17 * 0.14 * 0.14 * 12 = 3.783192
Let's round to 3.7832 inches.

75 feet = .5 * 32.17 * 0.07 * 0.07 * 12 = 0.945798
Let's round to 0.9458 inch.

Now, let's start with our sighting system at our bore line and tilt it to coincide optically with the point of bullet drop at 50 yards (3.7832 inches down). This would bring it down half that amount at 25 yards; 1.8916 inches. This would overshoot the 25 yard bullet drop by 0.9458 inch, since the original drop was 0.9458 inch at 25 yards.

To adjust the 25 yard zero, keeping the 50 yard optically set, you would raise the sighting system a distance equal to twice the discrepancy at 25 yards; 1.8916 inches. This would align the sighting system with both the 25 yard and 50 yard "calculated" impact points.

Notice the relationship between the calculated sighting system height and the 50 yard bullet drop - 1.8916:3.7832 = 1:2

Therefore, it appears that the ideal sighting system height above bore line to have the same zero at 25 and 50 yards, is one-half the distance of the 50 yard bullet drop.

I've tried this with several velocities above and below the 1070 and it seems to hold true.

May the mathematicians prove or disprove my above fiddlings...


Next let's explore the practical side of this:

All kinds of factors about the air density will lead to variations in friction which in turn slow the bullet to varying degrees. At our distances and velocities, will they matter that much?

My 208s with an Ultradot on top seems to be within a couple clicks of zero at all three distances I shoot. And those couple of clicks are probably not a result of air density. My scope is mounted close to 1.4 inches above the center line of the bore. I thought I'd try some more math to determine what the "calculated" error should be at 25 yards and 50 feet, if the gun is zeroed at 50 yards. Here are my calculations:

I'll start with the same 1070 velocity for the ammo, which will produce the same values as above for transit time, bullet drop, etc.

The only addition to the above will be the calculations for the 50 foot drop:

Transit time for 50 feet is 50/1070 = 0.0467289719626 and a few more digits.
Let's round to 0.04673 second.

The 50 foot drop is .5*32.17*0.04673*0.04673*12 = 0.421496403558
Let's round to 0.4215 inch.

Now let's compare how much we moved the 25 yard sight line compared to the corresponding bullet drop:

1.4 inches at the gun equals half that, or 0.7 inch at 25 yards, so we only came back .7 inch of the original 0.9458 inch. That's a difference of 0.2458 inch. So, we should expect about a one-quarter inch error at 25 yards, "mathematically."

How about at 50 feet?

First, we need to find the adjustment made at 50 feet when we corrected for 50 yards:

Our shift was 3.7832 inches down at 50 yards. This should equate to 1/3 of that for 50 feet, or 1.26106666 with lots more 6s.
Let's round to 1.261 inches.

Now we'll subtract the drop - 1.261-0.4215 = 0.8395 inch.

If we came up 1.4 inches at the gun, at 50 feet it equates to 2/3 that, or 0.933333 with lots more 3s.
Let's round to 0.9333 inches.

Now to calculate the "technical" error, all we have to do is subtract - 0.9333-0.8395 = 0.0938 inch.

So, in effect, we're talking less than one-eighth inch at 50 feet for my setup.

That sems to fall in line with my practical experiences.


All comments are quite welcome, even those disputing everything I've written...

Take Care,
Ed Hall
US Air Force Shooting Teams
Bullseye (and International) Competition Things

[jackh]

Ed H
Mount the dot in a super low setup and also a real high mount. Shoot and compare 50 and 25 settings.

[Ed Hall]

Ed H
Mount the dot in a super low setup and also a real high mount. Shoot and compare 50 and 25 settings.

Hi Jack,

I've had low mounted scopes on two other .22s and did scope adjusts for 50/25/50 in the past. (I still do with my .45s, but those bullets are slower, so the height above bore would be a bit much - smile.) I'm happy with the way my 208s stays zeroed as it is. I'll wait for any further input from others who would like to test out the numbers. I've stopped testing all the different things and now try to spend my time training. Even my Rika and my Chrony have dust on them - not as much on the Rika. And, I sent my guns out to a "real" gunsmith, the last time they needed some tweaking.

Take Care,
Ed Hall
US Air Force Shooting Teams
Bullseye (and International) Competition Things

[alb]

In doing some math for this addendum, I stumbled across something that seems too simple to be correct, yet appears to calculate out. I invite all the mathematicians to jump in and dispute or validate my findings.

Using a ballistics calculator, and assuming a muzzle velocity of 1,070 fps, standard atmosphere and a ballistic coefficient of 0.1 (G1) for .22 ammunition, I got a sight height of 2.14 inches above the center of the bore in order to produce a near zero at 25 yards and a far zero at 50 yards. This, of course, includes the effects of drag, and is reasonably close to your calculations without drag.

For a .45, assuming a muzzle velocity of 750 fps, standard atmosphere and a ballistic coefficient of 0.15 (G1), I got a sight height of 4.05 inches above the center of the bore in order to produce a near zero at 25 yards and a far zero at 50 yards.

1,070 fps is actually a fairly hot load, and is definitely in the transsonic range (not good for accuracy). With my Pardini, the Federal 745 gives me a muzzle velocity of 1,050 fps. RWS Target Rifle (the recommended ammunition for the Pardini) gives me a muzzle velocity of 857 fps (definitely better for accuracy). But, with this muzzle velocity, assuming the same atmosphere and ballistic coefficient, I would need to have my sight 3.18 inches above the center of the bore to produce zeros at 25 and 50 yards.

Regards,

Al B.

[Ed Hall]

Hi Al B,

Thanks for checking out my numbers. I am a bit confused by your reference to 1070 fps as being transsonic. Isn't the speed of sound around 1130 in dry air at 70 degrees and sea level? All the definitions of standard velocity ammo have stated the velocity as between 1050 and 1100, or thereabouts. However, I do seem to remember a discussion about the 208s with the US rep, where he told me that the best accuracy for that gun usually displayed itself at around 1000 fps. I'll have to check out some of my old notes to see what measured velocity I had for my better tests...

Anyway, thanks again for the check on my numbers.

Take Care,
Ed Hall
US Air Force Shooting Teams
Bullseye (and International) Competition Things

[alb]

I am a bit confused by your reference to 1070 fps as being transsonic. Isn't the speed of sound around 1130 in dry air at 70 degrees and sea level? All the definitions of standard velocity ammo have stated the velocity as between 1050 and 1100, or thereabouts. However, I do seem to remember a discussion about the 208s with the US rep, where he told me that the best accuracy for that gun usually displayed itself at around 1000 fps. I'll have to check out some of my old notes to see what measured velocity I had for my better tests...

Hi Ed,

The speed of sound in a standard atmosphere (59 degrees F., 0 percent humidity and at sea level) is 1115 fps, so you are correct about that.

'Transonic' refers to a range of velocities, ranging from 0.75 Mach to 1.20 Mach, or about 840 fps to about 1,344 fps, where the air flow over some parts of the projectile is supersonic, while it is subsonic over other parts of the projectile. This creates considerable turbulence and is bad for accuracy.

I chronographed a number of different types of .22 ammunition out of my Pardini with its 4 inch barrel. The velocities were considerably lower than the specified velocities for the same ammunition shot from a rifle with a 28 inch barrel. Based on this, a round with a stated velocity of 1,000 fps (rifle) would have a velocity when fired from a pistol that would be somewhere around 850 fps, right at the bottom of the transonic range, which again agrees with what you are saying about the 208s.

Regards,

Al B.

[Ed Hall]

Hi Al B,

Thanks again. I did some looking back in my notes and discovered that velocity-wise my worst and best tests didn't differ much. Here are some high points:

This is all from my 208s at 50 yards.

My best group was .78 inch, average velocity 987.01 fps, highest 1003.00 fps, lowest 966.90 fps.

My next best was 1.06 inches with an average of 973.30 fps - no further data available.

And, third was 1.18 inches with an average of 957.60 fps - no further data available.

Oddly, my worst of the tests had a group size of 3.04 inches with an average of 991.35 fps, highest 1014.00 fps, lowest 971.10 fps.

The lowest average velocity of all the tests showed 929.60 fps, and that ammo gave me a group size of 1.80 inches.

I guess I haven't fired anything as slow as some of your ammo, at least not in any testing, but then again, the 208s barrel is slightly longer than the Pardini's.

Take Care,
Ed Hall
US Air Force Shooting Teams
Bullseye (and International) Competition Things

[alb]

Hi Ed,

How many shots per group did you fire? The reason that I'm asking is that standard practice seems to be to shoot 3, 5 or 10 shot groups. However, there is a significant amount of variance in group size when you do this, as a result of pure randomness.

A better way to test for accuracy is to shoot 50-shot groups and drop the worst 2 shots. The result produces a very reliable measure of accuracy with very low variance. In fact, when the military does accuracy testing on artillery rounds, they use circular error probability (CEP), which measures the diameter of the covering circle for the best 50 percent of the shots. This produces an extremely reliable measure with only 20 shots. The reason is that you are dropping all of the low probability shots.

Unfortunately, CEP is not practical for small arms testing, where the result is generally a single ragged hole with only a couple of outliers.

Also, the more shots that you shoot per group, the larger the average group size, so 5-shot groups aren't really comparable to 10-shot groups. And groups where you drop a different number of shots aren't comparable to each other either.

Also, a spread of 967 fps to 1,003 fps will produce a vertical spread of 0.16 inces at 50 yards.

Regards,

Al B.

[Ed Hall]

Hi Al B,

All my testing is done with ten shots groups and measured center to center. I don't throw anything out - none of the matches I shoot do.

Also, a spread of 967 fps to 1,003 fps will produce a vertical spread of 0.16 inces at 50 yards.

In practical testing I have not found any correlation between small variations in velocity and resultant hits. It seems that the barrel oscillation has more effect than trajectory, although they must be intermixed to some degree. I've also found group size unrelated to extreme spread, until that spread really is "extreme."

Take Care,
Ed Hall
U.S. Air Force Competitive Shooting Teams
Bullseye (and International) Competition Things

[2650 Plus]

Ed ,I cant stand it any longer so I'm going to pick a nit about your above post. Would the time you spent working out the Sight settings have been better spent on the range having fun popping primers and scoring the targets ? Or as Steve might say "geeze". Good Shooting Bill Horton

[Ed Hall]

Ed ,I cant stand it any longer so I'm going to pick a nit about your above post. Would the time you spent working out the Sight settings have been better spent on the range having fun popping primers and scoring the targets ? Or as Steve might say "geeze". Good Shooting Bill Horton

Hi Bill,

You're quite right, Bill! But, math and TT posting are also hobbies. In fact, all the gathered data I'm quoting from is somewhat old. I haven't had my Chrony out or done any ammo testing in years. Unfortunately, I still can't do any Outdoor training yet either up here in the North Country. And, my lead level got high, so I had to limit my Indoor range use as well.

I do have to admit to a time when I did all kinds of testing, experimenting, etc. But after I concluded I had enough info, I scaled it back considerably. Now I'm pretty well settled on all my loads, brands, etc.

Thanks for the note, and for trying to keep me on track.

Take Care,
Ed Hall
US Air Force Shooting Teams
Bullseye (and International) Competition Things

[Guest]

Not to hijack the thread, but Ed, do you care to elaborate on the high lead levels? How discovered, how are you mitigating? Any recommendations for the rest of us? Thank You.

[Ed Hall]

Not to hijack the thread, but Ed, do you care to elaborate on the high lead levels? How discovered, how are you mitigating? Any recommendations for the rest of us? Thank You.

Basically, if you look at the lists of symptoms of lead poisoning, I was experiencing a large number of them in very minor ways. This was a while after replacing the metal and sand in an indoor range. Although I wore a full cover suit and lead rated dust mask, I blame that work for the spike.

I started wearing the mask for all Indoor shooting, reduced my Indoor range time to once a week and drank lots of reconstituted milk. I must point out that my level was not at an extreme high, that I know of. The highest of the values documented was 29 ug/dL, although I suspect it was on its way down when measured.

My doctor also dismissed my symptoms being as lead caused, but since most of them abated as my level came down, I'm sticking with that theory.

First, don't panic! Just follow the advice given in prior threads, such as cleanliness and range operation. Also, if you find a sweet taste in the back of your throat after shooting Indoors, check into the ventilation of your range, and consider wearing a lead rated dust mask. And, don't sweep without a mask...

Take Care,
Ed Hall
U.S. Air Force Competitive Shooting Teams
Bullseye (and International) Competition Things