Do Test Groups' MOA Size Change With Range?

Colorado Redneck said:
The outer third comprises about 55percent of the area of a circle. Assuming random dispersion, then yes. My limited observations are, however, that in a larger number of shots, most are clustered closer to the center of the group.
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My data from analyzing such groups is...

40% of the shots are inside the inner 40% of group diameter. 30% in the next 30%, same for next 20% and 10%. Tracks well with statistical distribution curves.

Why are tuners used at the muzzle on some rifles? What do they change?
 
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A 10 shot group being 1 MOA is kind of miraculous by itself. However, if the question is will the same ammo and rifle produce 1" at 200 or 300 yards, then no.
"...and precession..." That's normally called pitching and yawing. The base of the bullet literally wobbles until the rifling twist takes effect and the bullet stabilizes. That's at around 300 yards for a .30 calibre.
Arrows do the same thing. You can see an arrow stabilize when the fletching kicks in. It's like a switch was thrown. The arrow's back end stops wobbling and starts flying true.
 
The longer the bullet is out of the bore, the more opportunity things like wind and gravity have to change the path of the bullet. Therefore, with sufficient sample sizes, (i.e. enough groups shot and compared) the MOA measurement of groups at longer ranges should be larger than groups shot at shorter ranges under identical conditions. Maybe not a lot bigger, but some.

There are some circumstances under which a rifle might, under nearly ideal conditions, make groups that are about the same, measured in MOA at one particular farther range, but that's sort of a pathological case. Still interesting to consider.
Exactly one inch is good enough for the National Shooting Sports Foundation.
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https://www.nssf.org/shooting/minute-angle-moa/
"A MOA is 1/60th of a degree.

1 MOA spreads about 1″ per 100 yards. (actually 1.047″)"​
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:
  • Using 3 instead of the correct value for pi.
  • Approximating 100 yards as 95.5 yards.
  • Approximating a minute of angle as being 1/63rd of a degree instead of 1/60th of a degree.
In practice, a 5% approximation error is not a big deal given that there's probably around that much error in the actual group size measurements before one starts calculating the MOA values. And, of course, if everyone is using the same approximation by standard, then it's not an issue at all.
 
T. O'Heir said:
The base of the bullet literally wobbles until the rifling twist takes effect and the bullet stabilizes. That's at around 300 yards for a .30 calibre.
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Then why do the best 30 caliber match bullets test .20 MOA at 100 yards, .25 MOA at 200 or .30 MOA at 300? I've seen 30 caliber match bullet test groups shot at Sierra's 100 yard range in California averaging 1/10th inch.

Benchrest aggregate group average records expand about the same from 100 to 300 yards. Their single 5 and 10 shot group records are smaller.
 
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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 .
 
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:
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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.
 
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!
 
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.
 
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
 
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.
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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:eek:. 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
 
ernie8 said:
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 .
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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.
 
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.
 
Road_Clam said:
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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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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TXAZ said:
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'.
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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.
 
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."
 
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.
 
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stagpanther said:
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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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.
 
Note a given wind in the first third of target range causes more drift on target than the same wind in the last third.
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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.:D

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?:)

And wind above the line of sight is faster than in it, varies with terrain.
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Most of the time--but there are exceptions :D
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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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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