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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Riddle me this? Ballistic calc vs reality mismatch...
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<blockquote data-quote="entoptics" data-source="post: 1981068" data-attributes="member: 104268"><p>To address various questions first...</p><p></p><p>[USER=113338]@OutsideSeth[/USER] [USER=19988]@Stgraves260[/USER] [USER=94479]@smokey3[/USER]</p><p>The 2° slope (taken from Fury 5000) was included in the calculation (rangefinder in Line of Sight Mode, so not double counted), though it's less than 0.1" difference at 500 yds, and certainly not 6 feet. 5° incline wouldn't be 6 feet either. 6 feet in 2 yards (6 feet) would require the bullet traveling down at a 45° angle...</p><p></p><p>Smoke definitely affected range finder, but only in that I had to be careful getting a good return ("LAST" setting). I shoot at this location all the time, so I almost don't need to range the 200 and 500 targets, as I setup in the same spot (can even put the rebar stand in the same holes). I range anyway, to ensure I didn't lay my mat down a foot or two forward or back from "average".</p><p></p><p>The targets were in a line, and the rifle/bipod/bags didn't move throughout the course of fire.</p><p></p><p>Coriolis was used in Ballistic (Not an option in 4DOF or JBM), but only accounts for 0.05 MOA at 500 yds shooting east anyway.</p><p></p><p>Mentioned in OP, but folks seem to have missed it. The scope passed a box test at 100 yds a couple weeks ago. 20x12 MOA, round robin fired, correct and square within measurement error. The scope has internal levels, and I use a plumb bob on the target also, so cant isn't an issue.</p><p></p><p>Sight height was calculated from bore center, by measuring from the top of mounted scope to the bottom of barrel (stock removed), then subtracting half the scope diameter and half the barrel diameter at the measurement location. It's close enough for government work...</p><p></p><p><strong>So...On to results of my retest yesterday...</strong></p><p></p><p><em>Summary - things came closer to alignment, so the first sessions results are going into the "worrisome aberration" category, though I'm still a little concerned.</em></p><p></p><p>This time around, I only had time for 6 shot groups, but I fired them round robin style at 200, 500, and 628 yards. I also took 1/4 MOA off of Monday's zero, as that group was a little higher than center. With only 5-6 shots per group, the results don't have as much statistical power as I'd like, but it is what it is...</p><p></p><p>200 yard "zero" group. Missing one bullet, as I got distracted by a phone call, and failed to strip off 500 yard dope for one shot (over the top of target).</p><p>[ATTACH=full]214416[/ATTACH]</p><p></p><p>This is showing ~1/4 MOA high, and is a little disturbing, as the first 3 shots are the ones in orange (0.17 MOA group), and last two printed high. Not sure if this is meaningful (intermittent scope issue?), or just within random variation. Another example of how a single 3 shot group is almost completely meaningless.</p><p></p><p>Here's the 500 yard target. Also lost one shot high due to distraction and leaving 628 yard dope on (dogs this time).</p><p></p><p>Essentially perfect agreement with software's recommendation of 6.75 MOA.</p><p>[ATTACH=full]214417[/ATTACH]</p><p></p><p>And here's the 628 yard target. Software recommended ~10.25 MOA, which was dialed.</p><p>[ATTACH=full]214418[/ATTACH]</p><p></p><p>This one is higher than I'd like to see at ~0.4 MOA. BC would need to go from 0.7 to ~0.8 to or velocity from 2900 to ~2950 fps account for this.</p><p></p><p>At this point, I'm out of time/bullets, so I will take this information in mind as I begin field practice. I'll probably knock another 1/4 off my zero, and add a whisker of BC to my calculations. After I accumulate a "group" of a couple dozen cold bore shots at various ranges, I can see if I'm consistently high/low and adjust my DOPE accordingly. Assuming Bambi even presents himself at a distance beyond 500 yds...</p></blockquote><p></p>
[QUOTE="entoptics, post: 1981068, member: 104268"] To address various questions first... [USER=113338]@OutsideSeth[/USER] [USER=19988]@Stgraves260[/USER] [USER=94479]@smokey3[/USER] The 2° slope (taken from Fury 5000) was included in the calculation (rangefinder in Line of Sight Mode, so not double counted), though it's less than 0.1" difference at 500 yds, and certainly not 6 feet. 5° incline wouldn't be 6 feet either. 6 feet in 2 yards (6 feet) would require the bullet traveling down at a 45° angle... Smoke definitely affected range finder, but only in that I had to be careful getting a good return ("LAST" setting). I shoot at this location all the time, so I almost don't need to range the 200 and 500 targets, as I setup in the same spot (can even put the rebar stand in the same holes). I range anyway, to ensure I didn't lay my mat down a foot or two forward or back from "average". The targets were in a line, and the rifle/bipod/bags didn't move throughout the course of fire. Coriolis was used in Ballistic (Not an option in 4DOF or JBM), but only accounts for 0.05 MOA at 500 yds shooting east anyway. Mentioned in OP, but folks seem to have missed it. The scope passed a box test at 100 yds a couple weeks ago. 20x12 MOA, round robin fired, correct and square within measurement error. The scope has internal levels, and I use a plumb bob on the target also, so cant isn't an issue. Sight height was calculated from bore center, by measuring from the top of mounted scope to the bottom of barrel (stock removed), then subtracting half the scope diameter and half the barrel diameter at the measurement location. It's close enough for government work... [B]So...On to results of my retest yesterday...[/B] [I]Summary - things came closer to alignment, so the first sessions results are going into the "worrisome aberration" category, though I'm still a little concerned.[/I] This time around, I only had time for 6 shot groups, but I fired them round robin style at 200, 500, and 628 yards. I also took 1/4 MOA off of Monday's zero, as that group was a little higher than center. With only 5-6 shots per group, the results don't have as much statistical power as I'd like, but it is what it is... 200 yard "zero" group. Missing one bullet, as I got distracted by a phone call, and failed to strip off 500 yard dope for one shot (over the top of target). [ATTACH type="full" alt="IMG_5031.JPG"]214416[/ATTACH] This is showing ~1/4 MOA high, and is a little disturbing, as the first 3 shots are the ones in orange (0.17 MOA group), and last two printed high. Not sure if this is meaningful (intermittent scope issue?), or just within random variation. Another example of how a single 3 shot group is almost completely meaningless. Here's the 500 yard target. Also lost one shot high due to distraction and leaving 628 yard dope on (dogs this time). Essentially perfect agreement with software's recommendation of 6.75 MOA. [ATTACH type="full" alt="IMG_5033.JPG"]214417[/ATTACH] And here's the 628 yard target. Software recommended ~10.25 MOA, which was dialed. [ATTACH type="full" alt="IMG_5034.JPG"]214418[/ATTACH] This one is higher than I'd like to see at ~0.4 MOA. BC would need to go from 0.7 to ~0.8 to or velocity from 2900 to ~2950 fps account for this. At this point, I'm out of time/bullets, so I will take this information in mind as I begin field practice. I'll probably knock another 1/4 off my zero, and add a whisker of BC to my calculations. After I accumulate a "group" of a couple dozen cold bore shots at various ranges, I can see if I'm consistently high/low and adjust my DOPE accordingly. Assuming Bambi even presents himself at a distance beyond 500 yds... [/QUOTE]
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Riddle me this? Ballistic calc vs reality mismatch...
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