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Unread 04-04-2006, 10:49 AM
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...without knowing your situation/ relationship with coalition forces.....I would have thought the best place for this data would be co-located military units using the same weapons and ammo [img]/ubbthreads/images/graemlins/confused.gif[/img] have you explored this option?!

PS: (as a dumb Brit assuming that these are standard issue US sniper weapons with standard issue ammo) ....surely this data is published in the relevant US military training pamphlets too (most of which seem to be available on-line)? ...it is in the equivalent Brit publications.

..and I wouldn't be too fussy about the data...you're never going to get better than 'in the parish' if you're limited to 25m for all your zeroing and range work! (I hope 'accurate' and 'exact' to 1000m are not actually too 'critical'!! [img]/ubbthreads/images/graemlins/smile.gif[/img] )

.....talking of 'in the parish'and relating it to your use of 'accurate, exact and Critical' ...(and, based on my very limited experience of working 'around' civilian contractors in Iraq)...might be worth pointing out that dependant on your situation in terms of your legal status, the ROE under which you are operating and the requirements of the situation/incident itself, you might want/need to consider the legal ramifications if you 'botch' an engagement (ie kill a friendly or an innocent) using a rifle that has only ever been zeroed at 25m and then set using (what has been kindly described above as) 'SWAP' data.

Good Luck! [img]/ubbthreads/images/graemlins/smile.gif[/img]
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Unread 04-04-2006, 03:31 PM
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Given, the limitations I described earlier, if it's of any immediate use, here's a quick eg of the sort of 25m zeroing target you will have to produce (written dimensions are correct with the data shown, line spacings diagrammatic only)....hard to discern the elevation differences when you start to put 308 bullet holes on it!
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Unread 04-04-2006, 04:39 PM
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He makes no mention of the differances between army and marines mildot reticles, and uses the math indescriminately too!!!!
And the list goes on and on...
Now my plaster book is full of notes in the margins on what is wrong

[/ QUOTE ]

I noticed that too. That is, once I learned that there was a difference. I also have the first US video and if the data in the book is of the same quality as the video then it would cause serious doubts about the quality of the rest of the info as it relates to long range techniques and gear. I learn something every day here at LRH.

But I suppose that is something I should ask in another thread. (I didn't mean to cause a topic hyjack.)
GRAVITY. It's not just a good idea. It's the LAW!
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Unread 04-04-2006, 07:42 PM
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Here’s the come ups for both rifle-sight combinations from 100-yard zeros. Sierra’s 1996 software was used and it’s proved very, very accurate getting come ups from my own 100-yard zeros in four .308 Win. rifles using their 155, 168, 180, 190 and 200 gr. 30 caliber match bullets. But only when accurate muzzle velocity data is known. With variables such as bore, groove and chamber dimensions, these will effect a given round’s muzzle velocity. And then you add powder temperature at firing (heated from spending a while in a hot barrel or storage/carrying place, more changes to muzzle velocity will happen. And the difference in air temperature for each 10-degree F change even at 1000 yards is only 6/10ths MOA at most. As there’s probably going to be enough actual muzzle velocity than the numbers I used to make that much difference, I’m going to use three 20-degree temperature bands. But this data is at least a starting point. It would be interesting to see how it compares to others provided.

The info below is grouped by each rifle (20-inch then 24-inch barrels), then by ranges starting at 200 yards and every 100 yards out to 1000. Each range will have a 20-degree temperature band with the come up. Here’s an example for come-ups from a 100 yard zero to 500 yards for the 24-inch barrel:

“800 yd: 85-105F=28.7 moa, 106-125F=26.1 moa, 126-145F=25.0 moa

If the range is 800 yards and the temperature is 109 degrees F, come up 26 MOA from the 100 yard zero. You’ll hit within 4 inches vertically if your actual muzzle velocity is 2600 fps.

Heres the numbers:

SR25 with 20-inch barrel, sight height 2.5 inches, M118 with 173-gr. M2 bullet leaving at 2500 fps
At 25 yards, impact is 1.3 inches low for a 100-yard zero
Come ups from 100-yard zero
200 yds; 85-105F=1.9 moa, 106-125F=1.9 moa, 126-145F=1.9 moa
300 yds; 85-105F=5.0 moa, 106-125F=5.0 moa, 126-145F=4.9 moa
400 yds; 85-105F=8.6 moa, 106-125F=8.5 moa, 126-145F=8.3 moa
500 yds; 85-105F=12.7 moa, 106-125F=12.6 moa, 126-145F=12.2 moa
600 yds; 85-105F=17.4 moa, 106-125F=17.1 moa, 126-145F=16.5 moa
700 yds; 85-105F=22.5 moa, 106-125F=22.1 moa, 126-145F=21.3 moa
800 yds; 85-105F=28.4 moa, 106-125F=27.7 moa, 126-145F=26.5 moa
900 yds; 85-105F=34.9 moa, 106-125F=33.9 moa, 126-145F=32.3 moa
1000 yds; 85-105F=42.2 moa, 106-125F=40.9 moa, 126-145F=38.6 moa

M24 with 24-inch barrel, sight height 1.5 inches, M118 with 173-gr. M2 bullet leaving at 2600 fps
At 25 yards, impact is 0.6 inch low for a 100-yard zero
Come ups from 100-yard zero
200 yds; 85-105F=2.2 moa, 106-125F=2.1 moa, 126-145F=2.1 moa
300 yds; 85-105F=5.1 moa, 106-125F=5.1 moa, 126-145F=5.0 moa
400 yds; 85-105F=8.5 moa, 106-125F=8.5 moa, 126-145F=8.3 moa
500 yds; 85-105F=12.4 moa, 106-125F=12.2 moa, 126-145F=11.9 moa
600 yds; 85-105F=16.6 moa, 106-125F=16.4 moa, 126-145F=15.9 moa
700 yds; 85-105F=21.4 moa, 106-125F=21.0 moa, 126-145F=20.2 moa
800 yds; 85-105F=26.7 moa, 106-125F=26.1 moa, 126-145F=25.0 moa
900 yds; 85-105F=32.6 moa, 106-125F=31.8 moa, 126-145F=30.3 moa
1000 yds; 85-105F=39.3 moa, 106-125F=38.2 moa, 126-145F=36.1 moa

Here’s wind correction data using the old military formula Range (in hundreds of yards) times Wind speed (in mph) divided by the range constant for the MOA correction for a full value wind from 3 or 9 o’clock. For other wind angles, take a fraction of the answer. Example: at 900 yards with a 13 mph wind from 1 o’clock, 9 times 13 is 117, then dividing 117 by the 900 yard constant of 11 equals almost 8, and a 1 o’clock wind is worth 50% of full value, so you would put on 4 minutes of right wind correction and would be within a couple of inches of what’s exact for Sierra’s calculations.

100 and 200 yards, constant is 15
300 and 400 yards, constant is 14
500 and 600 yards, constant is 13
700 and 800 yards, constant is 12
900 and 1000 yards, constant is 11

Wind from 12:30, 5:30, 6:30 and 11:30 o’clock, 25% of full value (or quarter value wind)
Wind from 1, 5, 7, and 11 o’clock; 50% of full value (or half value wind)
Wind from 1:30, 4:30, 7:30 and 10:30 o’clock, 75% of full value (or three-quarter value wind)
Wind from 2, 4, 8, and 10 o’clock; 87% of full value (or a seven-eigths value wind)

Let me know how these numbers work out.
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Unread 04-06-2006, 12:36 AM
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Thank you all very much for the info. Carlock, I will be emailing you shortly. sometimes I have some difficulties retrieving and sending email on certain days so if you do not get a timely reply bear that in mind.

The guys got out to an airfield and got a hundred yard confirmation. This info will help quite a bit.

Thanks everyone.

More will follow.
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Unread 04-06-2006, 01:48 AM
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re-reading this thread , realised I'd had a brainfart on my 25m target line placement [img]/ubbthreads/images/graemlins/blush.gif[/img] , should be:

Now you have access to a 100yd range (what's wrong with a bit of remote desert?!), you can measure out, on a big piece of paper (!) a target to these dimensions (I've converted it all to yds...note how my moa values differ from Bart's...this highlight's how this is all SWAG...remember the real-world implications I mentioned earlier!)

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Unread 04-06-2006, 07:00 AM
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...note how my moa values differ from Bart's...this highlight's how this is all SWAG...remember the real-world implications I mentioned earlier.

[/ QUOTE ]Wouldn't life be boring if everything was exactly the same? Good post, Brown Dog; thanks for correcting your stuff.

Here's another variable....scope adjustment accuracy. Ever calibrate a scope's adjustments to see how far each click really changed point of impact? I've done this by putting a yardstick out at 50 yards, then benching the scope and moving the adjustments over 20 to 30 inches on the yardstick. A small percentage error is common. Evidence that if one makes a 30 MOA come up, the line of sight may move anywhere between 28 and 32 MOA depending on the scope make and model. Every internally adjusted scope I've checked ain't exactly dead-on; they all are a bit off. But each one is pretty repeatable for each click/MOA moving the same amount.

This happens because of the mechanical design of the scope. The clicks per turn for the thread count of the adjustment isn't exact for the erector tube's movement about the objective lens' primary image for perfect fractional MOA changes. But most scopes are within a few percent of being exact.

Once you know your scope's exact change per click/MOA, then you can convert the come ups from tables such as these to exactly what your scope needs to do
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