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May 27, 2019, 07:46 PM | #26 | |
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May 27, 2019, 09:59 PM | #27 |
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To answer your literal question:
Yes the MOA drops with longer ranges. Why, because of factors that don't really come into play at shorter distances. I shoot at longer ranges, mostly 600 & 1,000 yards and out to a mile (1760 yards). 1 MOA bullet holes that touch at 100 yards are usually bigger than 1 MOA at 1,000 yards and beyond, when other factors come into play. The most obvious factor is wind. Shooting at 1,000 yards, you've got to judge the wind speed and direction along the entire path, and there's a fair chance it's not the same the whole way. An early attempt at 1 mile had substantially different wind speed and direction at 200, 1,000 and at the target. 2.4 seconds is a long time and distance for a bullet to be acted upon by other forces. If you can't read the wind and integrate the forces along the path, there's more error to deal with. Like Correllois, Magnus and others you don't know about, calculate or notice at 100 yards. And when the bullet goes from supersonic to subsonic well beyond 100 yards, you'll notice the accuracy hit past that point. Further, you're eyeball and optics can't see the target as sharply at 1,000 yards as at 100 yards, so your "MOA" increases, even if you were shooting a laser'. Good luck!
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May 28, 2019, 06:49 AM | #28 |
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I don't understand the post, is there a back story I'm missing. BartB already knows the answer to the question in the OP as well or better than anyone here.
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May 28, 2019, 07:42 AM | #29 |
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My, my, didn't we get a bit technical here? That's nice. I don't get to discuss these things with people I know, but I confess that I'm not as technical in the shooting game as a lot of you guys. Seems that many of you are well into precision shooting and I applaud you for your knowledge.
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May 28, 2019, 12:51 PM | #30 | |
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I had more money invested in the scope mount, rings and scope than I had invested in the rifle. And as advertised the builder etched his driver license number on the receiver. I had never imagine there were so many creative ways to build a rifle stronger and with fewer parts. And then I built a rifle thinking it would never be taken apart. Again, I loaded 12 difference loads of 10 rounds each and delivered the rifle. I ask the new owner to determine what the rifle liked. As always I had to call him; he said the rifle liked everything, and then he added the part about thinking he would never get the rifle apart. So I asked; "Why would he take the rifle apart after shooting it 120 times". He claimed it was no easier putting it back together, he did say he thought the rifle was too heavy. F. Guffey |
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June 3, 2019, 06:05 AM | #31 | |
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June 7, 2019, 06:44 AM | #32 |
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Typically what I observe with the average recreational shooter is if you have a rifle that will consistently shoot 1 moa at 100 yds, it tends to open up beyond "1 moa" as distance increases. The main factor is cross winds. My 100 yd "1 moa" rifle will typically yield about 1.5+ MOA at 600 yds. Spin drift starts to become a small variable adding to greater potential MOA spreads at midranges.
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June 7, 2019, 07:57 AM | #33 | |
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Muzzle velocity spread is the biggest contributor to group size. Use your ballistic software to see vertical spread in MOA for a 50 fps velocity spread. Drop difference can be 1/10 MOA at 100 yards, 2 MOA at 1000. Atmospheric variables such as subtle winds and air density have smaller effects. Group size in MOA typically increases about 10 to 15 percent for each 100 yards past the first one. Positive compensation of barrel vertical vibration shooting slower velocity bullets at higher angles above LOS than faster ones not considered, but it can happen. Groups at 600 yards can have smaller MOA vertically than those at 300 and 1000 yards. Last edited by Bart B.; June 7, 2019 at 09:07 AM. |
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June 7, 2019, 09:13 AM | #34 | |
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The error will be a small fraction of an MOA anyway, maybe 1/20th. |
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June 7, 2019, 10:15 AM | #35 |
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Very cool thread--nice comments Bart. I often read in many ballistics texts about wind causing a bullet to yaw or pitch (which are typically caused in an aircraft from control surfaces, which of course a bullet does not have). My understanding is that this is impossible as long as the projectile's velocity exceeds that of the wind component--instead it is the overall movement of the parcel of air which causes the bullet trajectory to "move."
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June 7, 2019, 10:19 AM | #36 |
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Problem you have shooting 1000yd is conditions. Short yardage BR is based on 5 targets shot in 5 relay and winner is based on average of those 5 targets.
Someone may test loads in ideal condition but that doesn't happen in a match. This is BR 5 shot group 1000yds. https://www.gunsamerica.com/digest/b...00-yard-group/ This is 10 shot group @ 1000yd http://bulletin.accurateshooter.com/...ory-be-amazed/
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June 7, 2019, 11:31 AM | #37 |
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Anyone who understands statistics knows why all 5 and 10 shot single group records will eventually get broken. Ditto for several group aggregates. It has been happening for decades. Both smallest and largest.
All the BR aggregate records are a few to several times bigger than the single 5 or 10 shot group records. Each one's biggest single group is several percent larger than the agg average size. Last edited by Bart B.; June 7, 2019 at 04:34 PM. |
June 7, 2019, 11:34 AM | #38 | |
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June 7, 2019, 11:57 AM | #39 | ||
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Let's assume that a given parcel of crosswind is exactly identical in the first 1/3 as the last third of a bullet's trajectory and similarly the same regardless of the bullet's drop (probably a statistical impossibility, but let's go with that for simplicity's sake). The only other meaningful variable that I can think of is projectile velocity--which being faster after muzzle exit I would think would mean less "dwell time" of the projectile in the crosswind parcel of air than there would be at a slower velocity towards the end of the trajectory path; hence more time in the parcel would result in more drift. What am I missing here? Quote:
Terrain induced turbulence, wind shears caused by convective surface heating, catabatic late-day winds and venturis being just a few examples, as well as cold air downdrafts.
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June 7, 2019, 02:30 PM | #40 |
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I gave up on wind calling years ago. My clubs 600 yd range is a multi directional wind vortex. A typical scenario is the 500 flags 1/2 value left to right , the 200 yd flags full value right to left. My solution ? Just friggin shoot the dam target ! Ocassionally i see a consistiant breeze all the way downrange and for this i am gaining some experience with intermittant windage holdovers . I have the utmost admiration for master wind calling. Thats a skillset that is learned from trial and error, not by watching a youtube vid....lol
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June 7, 2019, 02:57 PM | #41 | |
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June 7, 2019, 03:00 PM | #42 | |
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"Everyone speaks gun."--Robert O'Neill I am NOT an expert--I do not have any formal experience or certification in firearms use or testing; use any information I post at your own risk! Last edited by stagpanther; June 7, 2019 at 03:07 PM. |
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June 7, 2019, 03:03 PM | #43 |
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You were respectful. And right in your reasoning.
I used Sierra Bullets software that allows two bullets be compared and different winds in several range bands. With the bullet velocity slower at 667 yards than zero, it spends more time in the last third than the first third. A table with wind above LOS is attached. Last edited by Bart B.; June 7, 2019 at 03:59 PM. |
June 7, 2019, 08:51 PM | #44 |
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Bart, sure they can break records but to win match is more than just one 5 shot or 10 shot group.
It's no secret that record group is smaller then the other groups and that short yard they do shoot 5 targets in 5 relay same day. You have to write program figure that. F-Class seems to make big deal on records https://www.6mmbr.com/gunweek088.html https://www.rifleshootermag.com/edit...pionship/84431 https://www.ssusa.org/articles/2017/...e-competition/
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June 8, 2019, 12:04 AM | #45 |
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Cross wind accelerates the projectile sideways. The projectile keeps the side-way speed even the cross wind disappears. It will slow down but it will keep on moving sideways till impact. The cross wind happens nearer to the muzzle, the more time it will have to travel sideways. When calling the wind, you want to put more weighting on wind near you.
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June 8, 2019, 12:23 AM | #46 | |
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June 8, 2019, 06:12 AM | #47 | |
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Unless you're obtuse like me.
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"Everyone speaks gun."--Robert O'Neill I am NOT an expert--I do not have any formal experience or certification in firearms use or testing; use any information I post at your own risk! Last edited by stagpanther; June 8, 2019 at 06:42 AM. |
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June 8, 2019, 07:06 AM | #48 |
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The spin keeps the bullet stable.
Once you get something moving in a particular direction, it continues moving in that direction until something stops it. Newton's first law of motion and all that. Motion is velocity and velocity implies momentum (momentum is mass times velocity), so if the bullet moves sideways, it must have momentum in that direction. If it has momentum in a given direction, Newton's first law says it will keep moving that direction until something stops it. If you roll a ball across the floor and blow on it to change its direction, it doesn't immediately resume its original direction once you stop blowing on it--it will keep rolling on the new path until something else causes it to change direction again. So once a bullet is (moved sideways by/gains sideways momentum from) a crosswind, even if the crosswind goes away, it will still keep moving sideways until air friction stops it. Since it's moving sideways relatively slowly, there's very little air resistance in that direction to speak of and it's not going to be in the air long enough to be slowed significantly in terms of crossrange velocity. When looking at position plots (like the one under discussion), straight lines mean velocity with no acceleration. Curved lines mean acceleration is being imparted. So, on the plot, the parts of the traces that are curved are the areas where the bullet is being accelerated sideways by wind. The wind is applying a force to the bullet (or you could say accelerating it, since acceleration = force/mass) which is increasing its velocity in the direction of the wind. The straight lines (whether slanted or horizontal) show the areas where there is no acceleration (force) on the bullet due to wind. A horizontal line means no sideways velocity, a slanted straight line means a sideways velocity. It may seem a bit strange to think about sideways velocity being measured in inches per yard, but if you think about it, the horizontal axis could just as easily be labeled in terms of time (time of flight) and then you'd have inches per second which is obviously a measure of velocity.
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June 8, 2019, 07:35 AM | #49 | |
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https://www.nbrsa.org/short-range-group-world-records/ https://www.nbrsa.org/600-yard-world-records/ https://www.nbrsa.org/1000-yard-world-records/ Writing a program is not needed. Most people can use grade school mental math with paper and pencil doing addition and division averaging a few to several numbers. They did that in the 1950's and 1960's at benchrest matches. A hand held calculator can also be used; that started in the early 1970's, but only to speed up the process. Last edited by Bart B.; June 8, 2019 at 12:36 PM. |
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June 8, 2019, 07:49 AM | #50 | |
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The bullet is moving slower during the 700-1,000 yd phase of its flight, so for a given amount of sideways acceleration, you will get more sideways motion relative to forward motion than if you impart that same acceleration earlier in the flight where the bullet is moving downrange faster. Also, the bullet is spending longer in that region since its moving slower and therefore the wind has more time to act on the bullet. It's a combination of both of those things.
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