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May 27, 2019, 07:46 PM   #26
Jim Watson
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Quote:
 Approximating 1MOA as 1" results in an approximation error of about 5%. Not a big error. For reference, here are some other approximations that are about the same in magnitude:
And the Kewl Guys talk in mils. A milliradian is conveniently the angle that subtends 1/1000 of the distance. Two pi radians in a circle, 6283.285 mils to the geometer. 6280 to the old infantry, 6400 to the artillery and now NATO. 6000 Rusky, 6300 Swedish.

 May 27, 2019, 09:59 PM #27 TXAZ Senior Member   Join Date: September 5, 2010 Location: McMurdo Sound Texas Posts: 3,998 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! __________________ !أنا لست إرهابياً
 May 28, 2019, 06:49 AM #28 jmr40 Senior Member   Join Date: June 15, 2008 Location: Georgia Posts: 10,011 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. __________________ "If you're still doing things the same way you were doing them 10 years ago, you're doing it wrong" Winston Churchill
 May 28, 2019, 07:42 AM #29 Picher Senior Member   Join Date: December 14, 2004 Location: Maine Posts: 3,625 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. JP
May 28, 2019, 12:51 PM   #30
F. Guffey
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Quote:
 I know Bart cites "compensation" which works when barrel vibrations are just right to launch a low velocity bullet at a higher angle than a high velocity bullet, letting them both land close together at extended range, therefore a source of the converging bullet phenomenon. The Brits knew about that when they still shot the .303 at targets. Seems to me this would also mean that they were farther apart at midrange than the base group or the final group.
I bid on and won a rifle being sold on the Internet. Forum members had a field day; I could not see how a rifle could be that ugly without knowing what he was doing. I won the bid for \$120, if I was wrong I would still be ahead because of the parts. I loaded 12 different load of 10 rounds each and headed for the range. When it came to improving on the accuracy there was nothing I could do to improve it; there were no flyers, the groups moved but did not open up and some of the groups shared the same holes. I was told the rifle won the ugly rifle contest.

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

June 3, 2019, 06:05 AM   #31
rms65
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Posts: 59
Quote:
 Originally Posted by ernie8 Bench rest reported groups are factored from 100 to 200 yards , that is not the actual 200 yard measure . If you are shooting .10 groups with a factory mass produced bullet , .30 cal yet , you should go and win some side bets at a bench rest match . I am just glad all the super shooters do not shoot in matches , or I would be in trouble . Kind of like when I was running a pro class drag car in NHRA , people who built their motors with parts from Auto Zone told me how they were making more hp than my factory backed motors were . All my time wasted with blocks not even released to the public , flowed heads and handmade sheet metal intakes made to match , custom turned cam ,750 cfm carbs flowed to 1180 . In case there are any racers here , 314 sb chevy , 7.82 at 178.4 best at 11,500 rpm shift and a 7500 launch .
Ha too funny. And as an old motor head / street racer I know what you are talking about. There's a lot of delusional "experts" out there in every area of interest. And that's a VERY impressive car you put together.

 June 7, 2019, 06:44 AM #32 Road_Clam Senior Member   Join Date: November 21, 2013 Location: New Hampshire Posts: 1,478 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. __________________ "To be old an wise you must have been young and stupid"
June 7, 2019, 07:57 AM   #33
Bart B.
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Quote:
 Originally Posted by Road_Clam 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.
Spin drift is virtually constant at a given range. It is proportional with muzzle velocity spread. It increases with range. Bullet spin in rpm drops about 10% at 1000 yards, velocity about 60%.

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.
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Last edited by Bart B.; June 7, 2019 at 09:07 AM.

June 7, 2019, 09:13 AM   #34
Bart B.
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Quote:
 Originally Posted by TXAZ 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'.
That is a variable in the shooter aiming the rifle. Not an external ballistic variable this thread is about.

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 stagpanther Senior Member   Join Date: March 2, 2014 Posts: 7,458 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." __________________ If you’re ever hiking in the woods and you get lost, just look up and find the brightest star in the sky and you’ll know which way space is. 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!
 June 7, 2019, 10:19 AM #36 old roper Senior Member   Join Date: June 11, 2007 Posts: 1,976 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/ __________________ Semper Fi Vietnam 1965 VFW Life member NRA Life Member
 June 7, 2019, 11:31 AM #37 Bart B. Senior Member   Join Date: February 15, 2009 Posts: 7,999 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. __________________ US Navy Distinguished Marksman Badge 163 Former US Navy & Palma Rifle Team Member NRA High Power Master & Long Range High Master NRA Smallbore Prone Master Last edited by Bart B.; June 7, 2019 at 04:34 PM.
June 7, 2019, 11:34 AM   #38
Bart B.
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Quote:
 Originally Posted by stagpanther 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."
Note a given wind in the first third of target range causes more drift on target than the same wind in the last third. And wind above the line of sight is faster than in it, varies with terrain.
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June 7, 2019, 11:57 AM   #39
stagpanther
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Quote:
 Note a given wind in the first third of target range causes more drift on target than the same wind in the last third.
OK--this is purely a friendly discussion and I'm not challenging that outright (having zero proficiency at calling the wind myself LOL)--but I'm going to argue it anyway from the devil's advocate point of view.

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:
 And wind above the line of sight is faster than in it, varies with terrain.
Most of the time--but there are exceptions
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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If you’re ever hiking in the woods and you get lost, just look up and find the brightest star in the sky and you’ll know which way space is.
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 12:03 PM.

 June 7, 2019, 02:30 PM #40 Road_Clam Senior Member   Join Date: November 21, 2013 Location: New Hampshire Posts: 1,478 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 __________________ "To be old an wise you must have been young and stupid"
June 7, 2019, 02:57 PM   #41
Bart B.
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Quote:
 Originally Posted by stagpanther 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?
Does this help?
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 PSX_20180601_100231.jpg (105.5 KB, 127 views)
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June 7, 2019, 03:00 PM   #42
stagpanther
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Quote:
 Does this help?
I usually try to be respectful as I can in order to try to educate myself--my apologies if it didn't come across that way. But if you look at the magnitude of the drift from 0 to 300 vs the magnitude from 700 to 1,000--it looks roughly three times as much at the distant third??
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Last edited by stagpanther; June 7, 2019 at 03:07 PM.

June 7, 2019, 03:03 PM   #43
Bart B.
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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.
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Last edited by Bart B.; June 7, 2019 at 03:59 PM.

 June 7, 2019, 08:51 PM #44 old roper Senior Member   Join Date: June 11, 2007 Posts: 1,976 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/ __________________ Semper Fi Vietnam 1965 VFW Life member NRA Life Member
June 8, 2019, 12:04 AM   #45
tangolima
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Quote:
 Originally Posted by stagpanther What am I missing here?
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.

-TL

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June 8, 2019, 12:23 AM   #46
JohnKSa
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Quote:
 Does this help?
Great plot. It's one thing to know how something works--it's another thing to see it in full color. That tells the whole story in a way that's very easy to understand.
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June 8, 2019, 06:12 AM   #47
stagpanther
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Unless you're obtuse like me.

Quote:
 The projectile keeps the side-way speed even the cross wind disappears.
I truly had no idea that a crosswind vector could add it's own inertial energy vector to a projectile's path. (intuition tells me this is impossible--otherwise a projectile would become hopelessly destabilized by every bit of mixing air it encounters).
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If you’re ever hiking in the woods and you get lost, just look up and find the brightest star in the sky and you’ll know which way space is.
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Last edited by stagpanther; June 8, 2019 at 06:42 AM.

 June 8, 2019, 07:06 AM #48 JohnKSa Staff   Join Date: February 12, 2001 Location: DFW Area Posts: 23,122 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. __________________ Do you know about the TEXAS State Rifle Association?
June 8, 2019, 07:35 AM   #49
Bart B.
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Quote:
 Originally Posted by old roper 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.
I have known for decades that sometimes more than 5 targets are used in a match. Sometimes 10 shot groups are used. Same with 600 and 1000 yard events; for example:

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.

June 8, 2019, 07:49 AM   #50
JohnKSa
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Quote:
 But if you look at the magnitude of the drift from 0 to 300 vs the magnitude from 700 to 1,000--it looks roughly three times as much at the distant third??
Missed this earlier.

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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