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Shooting my 338 LM @ 2200 meter

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  #8  
Unread 03-08-2012, 05:31 PM
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Join Date: Jan 2010
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Re: Shooting my 338 LM @ 2200 meter

"I ended up at almost 6 MILS to reach the rock. My scope was at 14x so I guess it would be close to 10 MILS at 25x."

I wonder if the poster realizes that the lrs-1 reads correct mil at 12.5 power. at 25 it reads 1/2 mils. at 14 you cant use the dots for mathematical calculations unless you know its exact measure (can be done by looking at a tape at set distance (like 100 yrds)
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  •   #9  
    Unread 03-08-2012, 05:40 PM
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    Re: Shooting my 338 LM @ 2200 meter

    That's strange, but maybe true.
    But in the manual from Millett, it states that 1 MiL = 25x.

    I took a shot @ 1350 meters 2 weeks ago@ 25x, and used the dot's for holding the windage, it was spot on from what Shooter came up with.

    Maybe something is different with my new LRS-1. ???
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      #10  
    Unread 03-09-2012, 04:05 AM
    M67 M67 is offline
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    Re: Shooting my 338 LM @ 2200 meter

    Quote:
    the reason is in incorrect input.
    Undoubtedly, the question is simply what variable is SO wrong?
    I have done my share of lobbing 308 and 6.5mm to "impossible" range, almost always "sighting in" on the spot, as temperature measuerement is by nose and ass, and pressure by weater forecast, etc.. the 6.5 becomes effectively unspottable beyond 1500m as we do not have desert sand here.
    However:

    I have been pestering Yrcan over this and i am convinced that all the normal variables are accounted for and used well within accuracy that should yield less than 1/10 of the error we are seeing.

    Running my ovn dope i get between 40.0 and 44.0 mil UP, considering the probable met/env at Yrcans site.
    Changing variables

    Temperature: 1C is 0.015mil /
    Pressure: 1hPa is 0.044mil
    Direction: 90 vs 270 is 0.5mil
    headwind: 1m/s is 0.06mil
    velocity: 1m/s is 0.11mil
    Humidity: miniscule effect, and anyways close to 100% in all Yrcans shooting
    BC: 0.010 of G7 BC is 1.2mil (in comparison it is 0.3@1350m)
    Range: 10m is abouts 0.44mil

    As far as i can tell from experience with measuring all these variables, at distances beyond handheld lasers, range is by far the most challenging. I estimate Yrcans temp, press. and other measuerements to be accurate within 2-3units of measurement. Wind probably far better, as we can see there is very little wind anyway.
    Range has been remeasured using different maps, GPS, etc.
    For any probable error in variables other than BC, the range must be over 2300m, which it is not.

    Thus, as i see it we are left with BC, obviously very important at this flight time (5.3s)

    Quote:
    To add another issue to the equation is that there are variables that affect known variables, changing what you thought to be correct, especially at extreme range. Things like BC changes over the trajectory
    The question becomes then, does the G7 BC change with velocity, and does it change on the order of 0.02 units?
    Does it change at the speed of sound? After all the bullet is travelling 600m, and for 2 seconds, below the speed of sound. If this is the case, the only solution will be a custom drag model, or to tweak it with different BCs for different ranges, or to use a bullet that fits the existing drag model.
    Maybe the bullet enters a region of dynamic instability, and is coning , or some kind of limit cycle oscillatons - thus increasing drag?

    K

    Last edited by M67; 03-09-2012 at 04:06 AM. Reason: correcting typos
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      #11  
    Unread 03-09-2012, 09:56 AM
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    Location: Fort Worth, TX
    Posts: 159
    Re: Shooting my 338 LM @ 2200 meter

    Quote:
    Originally Posted by M67 View Post
    Undoubtedly, the question is simply what variable is SO wrong?
    I have done my share of lobbing 308 and 6.5mm to "impossible" range, almost always "sighting in" on the spot, as temperature measuerement is by nose and ass, and pressure by weater forecast, etc.. the 6.5 becomes effectively unspottable beyond 1500m as we do not have desert sand here.
    However:

    I have been pestering Yrcan over this and i am convinced that all the normal variables are accounted for and used well within accuracy that should yield less than 1/10 of the error we are seeing.

    Running my ovn dope i get between 40.0 and 44.0 mil UP, considering the probable met/env at Yrcans site.
    Changing variables

    Temperature: 1C is 0.015mil /
    Pressure: 1hPa is 0.044mil
    Direction: 90 vs 270 is 0.5mil
    headwind: 1m/s is 0.06mil
    velocity: 1m/s is 0.11mil
    Humidity: miniscule effect, and anyways close to 100% in all Yrcans shooting
    BC: 0.010 of G7 BC is 1.2mil (in comparison it is 0.3@1350m)
    Range: 10m is abouts 0.44mil

    As far as i can tell from experience with measuring all these variables, at distances beyond handheld lasers, range is by far the most challenging. I estimate Yrcans temp, press. and other measuerements to be accurate within 2-3units of measurement. Wind probably far better, as we can see there is very little wind anyway.
    Range has been remeasured using different maps, GPS, etc.
    For any probable error in variables other than BC, the range must be over 2300m, which it is not.

    Thus, as i see it we are left with BC, obviously very important at this flight time (5.3s)


    The question becomes then, does the G7 BC change with velocity, and does it change on the order of 0.02 units?
    Does it change at the speed of sound? After all the bullet is travelling 600m, and for 2 seconds, below the speed of sound. If this is the case, the only solution will be a custom drag model, or to tweak it with different BCs for different ranges, or to use a bullet that fits the existing drag model.
    Maybe the bullet enters a region of dynamic instability, and is coning , or some kind of limit cycle oscillatons - thus increasing drag?

    K
    My apologies as I do not know how to do the multiple quotes

    Quote:
    I estimate Yrcans temp, press. and other measuerements to be accurate within 2-3units of measurement. Wind probably far better, as we can see there is very little wind anyway.

    My impression in the video is that there is a fairly good wind. It can be heard in the Mic of the video camera, the ripples on the water and waves on the far shore dont strike me as calm conditions. I could be wrong but I have spent a lot of time on the water as a fishing guide in the past, and the water seems to have a fair wind over it. It also appears, it could be an illusion, that the spray from the bullet impact seems to go right and possibly toward the shooter upon settling after every shot, due to wind.

    Quote:
    The question becomes then, does the G7 BC change with velocity, and does it change on the order of 0.02 units?
    Does it change at the speed of sound? After all the bullet is travelling 600m, and for 2 seconds, below the speed of sound. If this is the case, the only solution will be a custom drag model, or to tweak it with different BCs for different ranges, or to use a bullet that fits the existing drag model.

    The bullets BC does change with velocity and it could easily change by more than .02 units at that distance. The bullets velocity is constantly getting slower and the BC is constantly changing as the velocity changes. If the bullet he is using has a BC of .780 that may be good to1000 yards, but will most likely not be a valid number for soloutions at 1800 or 2000 yards. At that distance he was shooting the bullet would be below 1000 fps and is possibly in a state of unstabilized yaw and who knows what else, further affecting the drag and velocity loss of the bullet.

    Shots like that are stretching the boundries of what the typical small arms cartridges can do with calculated predictable accuracy. Thats why Cpl Craig Harrisons 2475 meter and Rob Furlongs 2430 meter shots are so remarkable.
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      #12  
    Unread 03-09-2012, 10:26 AM
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    I guess you can't rule out issues with the scope. The OP ran the elevation adjustment nearly to the limit. The true elevation depends on the calibration of the turrets, which may not be constant over range. Also, optical distortion could be a factor. If the windage adjustment was also far from the optical centerline (possible, depending on bore/receiver/base alignment) then there will be an error due to either pincushion or barrel distortion, if present.
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      #13  
    Unread 03-09-2012, 10:40 AM
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    Join Date: Aug 2008
    Location: Fort Worth, TX
    Posts: 159
    Re: Shooting my 338 LM @ 2200 meter

    Quote:
    Originally Posted by bruce_ventura View Post
    I guess you can't rule out issues with the scope. The OP ran the elevation adjustment nearly to the limit. The true elevation depends on the calibration of the turrets, which may not be constant over range. Also, optical distortion could be a factor. If the windage adjustment was also far from the optical centerline (possible, depending on bore/receiver/base alignment) then there will be an error due to either pincushion or barrel distortion, if present.

    Bruce makes a great point that has been overlooked. All of what he stated above could be the culprit. Need a emoticon that shows slaping the forehead as in, "Duh, why didnt I think of that!" lol
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      #14  
    Unread 03-09-2012, 11:05 AM
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    Join Date: Nov 2008
    Location: SW Montana
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    Re: Shooting my 338 LM @ 2200 meter

    Your going to need multiple velocity banded BC's to reach that range accurately with Shooter or almost any program out there right now.
    Range is a big issue as well, there are a few hand held units that will be fine at that range.
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