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Extreme Long Range Hunting & Shooting (ELR)
Shooting my 338 LM @ 2200 meter
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<blockquote data-quote="M67" data-source="post: 625570" data-attributes="member: 26259"><p>Undoubtedly, the question is simply what variable is SO wrong? </p><p>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 ***, and pressure by weater forecast, etc.. the 6.5 becomes effectively unspottable beyond 1500m as we do not have desert sand here. </p><p>However:</p><p> </p><p>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.</p><p> </p><p>Running my ovn dope i get between 40.0 and 44.0 mil UP, considering the probable met/env at Yrcans site.</p><p>Changing variables</p><p> </p><p>Temperature: 1°C is 0.015mil /</p><p>Pressure: 1hPa is 0.044mil</p><p>Direction: 90 vs 270° is 0.5mil</p><p>headwind: 1m/s is 0.06mil</p><p>velocity: 1m/s is 0.11mil</p><p>Humidity: miniscule effect, and anyways close to 100% in all Yrcans shooting</p><p>BC: 0.010 of G7 BC is 1.2mil (in comparison it is 0.3@1350m)</p><p>Range: 10m is abouts 0.44mil</p><p> </p><p>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.</p><p>Range has been remeasured using different maps, GPS, etc.</p><p>For any probable error in variables other than BC, the range must be over 2300m, which it is not.</p><p> </p><p>Thus, as i see it we are left with BC, obviously very important at this flight time (5.3s)</p><p> </p><p></p><p>The question becomes then, does the G7 BC change with velocity, and does it change on the order of 0.02 units? </p><p>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.</p><p>Maybe the bullet enters a region of dynamic instability, and is coning , or some kind of limit cycle oscillatons - thus increasing drag?</p><p> </p><p>K</p></blockquote><p></p>
[QUOTE="M67, post: 625570, member: 26259"] 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 ***, 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: 1°C 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 [/QUOTE]
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Shooting my 338 LM @ 2200 meter
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