High Power Trajectory Confusion

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Hello,

After a long hiatus, I recently got back into High Power Service Rifle and am having a lot of fun (again). So far I have found a few issues with position and sight picture. My old sight picture caused a few issues the further back I went. As I work through the issues the rifle performance seems more in line with physics. With that in mind it seemed like a good idea to compare my actual elevation per a given yard line (200, 300, 600) with what trajectory applications would expect. The results are a lot further off from expectations...

The figure below shows what I'm referring to. First off - I'm trying to use 1/4 minute elevation clicks as an axis and distance as the other axis. The title shows the 300 and 600 difference between what I'm getting and strelok predicts (seems large to me). The strelok and gunData.org data appear to be minutes, so I'm multiplying by 4 to get to 1/4 minute sights. I also need to divide the gunData output respectively by 2, 3, and 6.

trajConfusion.jpg

About the ammo used - I am working through old (2003ish) black hills ammo 75 grain moly.

I would like to see my trajectory shapes match up a little better with the predictions.

Another interesting note - the data was generated at Pelham's 600 yard range. Each line is a little higher than the previous. I'm wondering if the elevation of each yard line could be causing the issue...

Any thoughts?

Anthony

Note: the attached thumbnail below has errors - the one above seems correct.
 

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I'm not a HP shooter or a ballistics expert by all means but I'm curious if you used a chronograph. Did you input all your own data into the calculators or did you use their generic info (temp, humidity, wind direction and speed, drag, atmosphere pressure, etc). At 100 - 200 yards I don't expect the data to have much variation but I wonder how much these factor at 600 yards.
 
I didn't plug in the level of data you're talking about - my assumption perhaps correct or incorrect is it will be a second order effect. I'm interested in getting there, but not just yet.

I don't have a chronograph yet; but would like the capability soon. Ideally, I'm actually hoping to scrounge up a tin can radar and try to capture SAR imagery on the trajectory. Not a radar expert, but perhaps it will work? It seems like the biggest question is can the tin can register something as small as 75 grain projectile. I'm assuming the cross section on a 75 grain projectile is relatively large, but I haven't done the numbers and it would be non-trivial (probably a few weeks of effort) for me to get to speed.

My initial question is really where is the dog leg in my data? The trajectory apps take bullet weight into account and it seems like all other data aside, there should be a dog leg.
 
I'm no expert either but I have found even data and calculators are only close enough for iron sights.
I'm not sure why but Strelok doesn't work well for me.
At my home range I can vary a minute or 2 in my 100 yard zero just because of the light or time of year.

I have used these average come ups and have done ok by me. Need some final adjustments to get dialed in. Although more times than not my inconsistency in sight alignment and trigger control adds more error in my adjustments that adjusting sights..
100-200 + 2MOA
200-300 +3MOA
300-600 +12MOA https://www.northeastshooters.com/vbulletin/threads/143705-Zeroing-in-an-AR-15-for-HP-competition
I went through this a few years ago. This post helped me out a,bit

I had a real confusing ballistic result with 22lr. I was shooting my 513t and wanted to rough zero
1150 fps 40 grain ammo. Ballistics said approx 2inches high from point of impact should get me poa/poi at 100 yards...well that worked out well got me all over the ten ring. Now ballistics said
For 200 yards I need to impact approx 6" high at 25 yards. Well when I went out to 200 I was still a good 14" low.? Not sure what happened but I came up 7 min and good to go.
 
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I haven't shot there yet, but the differing elevations at the firing points at Pelham shouldn't have any direct effect on the zeroes. They may have an indirect effect in that your position is slightly different (head position compensating for the up or down) than at say Nashua or Reading, when're true firing points are all more o r less at the same elevation.

Remember: everybody gets behind the rifle differently. For instance, my 200 yard standing zero is 1.5 minutes higher than my 200 yard sitting zero (service rifle). Doesn't make any sense until you take into account how different your head position is.

To make a long story short; I don't care what any computer or smartphone software tells me. 2-300 is up 3 minutes and 3-600 is up another 11-12 minutes.
 
Let me see if I can add some clarity to this. If you had a long hollow tube approx. 26" and you were looking through the center you would not see the paper sides so to speak and the two ends would be aligned, if you change your head position then you would realize it because you then have the paper to tell you that you're no longer aligned. Well with the rifle sights you obviously don't have the paper to alert you but could be just as easily misaligned without realizing it but the two round ends still appear to be aligned. So in short this is why head position is so important. Hopefully that adds some understanding to the importance of head position.
 
Sorry, no. It's not.

My point: rear sight aligned with front sight, both aligned with target. You have a straight line between your eye, and the target; the front and rear sights align the gun with this line. Now, if it's a "wetwware" or "fudge factor" thing, fine. And, I know that a tiny difference at the gun end makes a big difference downrange.
 
Sorry, no. It's not.

My point: rear sight aligned with front sight, both aligned with target. You have a straight line between your eye, and the target; the front and rear sights align the gun with this line. Now, if it's a "wetwware" or "fudge factor" thing, fine. And, I know that a tiny difference at the gun end makes a big difference downrange.

The rear sight is an aperature, so yes, unless your eye is perfectly centered (by good, consistent head position), there is somewhat of a fudge factor.
 
Thank you. I'm used to "open" sights, on the stuff I use that has more than just a bead.

You mean like a notch or u rear sight? They are tough to see and use. I know the old 1903 springfield rifles were shot well by the old timers, but I'm really glad we don't have to use them now.
The beauty of the aperature rear sight is that, for the most part, your brain automatically centers the post within it. It's almost a no-brainer at 200 yards, but more care needs to be taken with it at longer yardages.
 
Have you confirmed your 1/4 inch clicks are actually 1/4 inch? I don't know if this applies with iron sights, but with my current scoped long range set up I was seeing differences in actual vs predicted point of impact that I could not explain even after checking chronograph of speeds on two units. Set up a target on a four ft target backer. One 1" black spot near bottom, then 1" orange spots precisely 10", 20", 30" vertically above black spot. Set up at 100 yard using a level so spots all vertical, and confirmed rifle was sighted in at 100 yards. Then aiming each shot at the black spot, fired one shot at black spot. dialed in 10" (40 clicks) fired one shot. Added another 40 clicks (20" elevation) and fired one shot, then added another 40 clicks (30" elevation) and fired another shot. Reset sight to 100 yard zero, and repeated the four shots. I found that my elevation .25inch clicks were very consistently and repeatably closer to .27" than .25" Which at 300 was noticeable, and at 600 and 900 I expected a problem. I added a correction factor to my dope, (IIRC was 6%) and everything lined up. First attempt at 600 rang the gong, and first at 900 elevation was fine, (but I didn't hold enough into wind.)
 
I heard JCG call the rear sight a head alignment aid .
If you factor in your eye is the rear sight then depending on where you put your head in relation to distance from the peep
You will change the sight radius. I maybe wrong but I believe this is why the marines teach nose to charge handle ....easy to know your in the same spot.
 
Iron sights are iffy. If you can find issues of Rifle Magazine Lawrence F. Moore wrote an outstanding article on the repeatability of iron sights and I loaned him two of my Central sights made in Australia for his study. Iron sights have variable movements based on how far the sights are separated. The owner instructions with Centrals give you the adjustments with about 8 different sight to sight variations. Obviously the closer the sights the more the clicks are "worth" and the further away the "finer" the sights move.



View: https://drive.google.com/file/d/0B3vWwz0ljvP5VjljX29UQnY1TzA/view?usp=sharing

Note: typo in above says that Michaelsille is a 1000 yard range, it was 1500 yards.


The firing record indicated we tested from 30 Oct 82 till - 22 December 82 and IIRC correctly we shot Saturdays and Sundays when there would be minimum witnesses so guess I worked 7 weekends to help them. I learned a great deal about AMSAA operations at the same time. Give the above report a read, should keep you busy for several weeks.

When I conducted this testing the AMSAA Analyst wanted to know two things. One what the dispersion was with Russian manufacture ball ammo and how good the sights were in relation to hits at the indicated ranges of the sight. In the civilian world this is called accuracy. If you click on the + sign the presentation above will become larger.

At Aberdeen we wanted to test utilizing the sight and the lowest POA/POI position and then reshoot the test with the rear sight on the rifle cranked up to the appropriate range increments in meters to determine how close the group center was to the POA/POI.

Weaver saved all the targets and plotted all shots from POA/POI at each meter line and again each meter line with the sight set. In that way he could determine how well the AK-74 matched the actual testing and since Aberdeen Ranges are like five feet above sea level we were able to generate outstanding data weapon after weapon.

Knowing how data is accumulated if Weaver had desired he could have gone back and compared it to the M1 Garand and the M14 as the accumulation of data was mind boggling.

As indicated in the above you can download Weavers No 3 report that wasn't printed until 1990 and the first two reports were printed in I think it was 82 and 84?? Those reports are still classified I guess.

I also had to write up my impressions of the AK-74 from a evaluators standpoint which I can say while I liked certain aspects of the system I would not want to be tasked to utilize one in a combat scenario or even a hobby scenario as the rifle ejected brass about 30+ feet away out into marsh area and we didn't recover any. It was a reloaders nightmare. They were steel cased so no loss.

He wasn't interested in any hit probability officially though I did put it through a few sessions and I was not impressed with that capability.

The rifle was equipped with a scope mount however one was not supplied when the Military Intelligence came into possession of it. I would have loved to been able to scope it and take it to 1000 on the Romney Creek Range which was 2500 yards.

Now for the bad news. When I got to Aberdeen I learned from the Ballistics Lab that computer projections only correlate in the real world 5% of the time. For instance you might have one yard/meter line that correlates with what the computer says.
 
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