4
4 Liberty
Guest
If I shoot a 1 MOA group at 50 yards, will it be a 2 MOA group hitting a target behind it at 100 yards? Will it grow to 4 MOA at 200 yards?
John Kielly
Shari's fan club
First of all, MOA (Minute Of Angle) is a description of the arc of dispersal of a group, irrespective of distance. One MOA at 50 yards is usually equated to ½";1 MOA at 100 yards would equate to 1". The nit pickers will tell you that the value of 1 MOA at 100 yards is actually 1.047", but most of us manage with the approximation of 1" per 100 yards.
So, if you meant that if a group is ½" at 50 yards, would it be 1" at 100 yards & 2" at 200 yards, the answer is not necessarily so (& probably not likely).
A number of issues can contribute to tighter grouping at a shorter single distance by virtue of having less effect on the projectiles & subsequently attenuate the group at a greater rate than a direct proportion beyond that distance. Examples of that include velocity spread, barrel harmonics (there's likely a relationship between the two), wind direction & speed, topography across all distances, quality of ammunition components etc.
John
So, if you meant that if a group is ½" at 50 yards, would it be 1" at 100 yards & 2" at 200 yards, the answer is not necessarily so (& probably not likely).
A number of issues can contribute to tighter grouping at a shorter single distance by virtue of having less effect on the projectiles & subsequently attenuate the group at a greater rate than a direct proportion beyond that distance. Examples of that include velocity spread, barrel harmonics (there's likely a relationship between the two), wind direction & speed, topography across all distances, quality of ammunition components etc.
John
TomD
e publius unum
In the context of your question, John above is correct. The effect of dispersion as the bullet exits the barrel is linear with distance. But when a cross wind is figured in, groups will grow rapidly in MOA as well when yardage increases. The effect of wind increases as to the square of the distance so wind will push a bullet 16 times as far at 200 as at 50. (unless corrected for, and that is the whole point)
That's why there are so many wind flags at a BR shoot.
Below a shot taken at Riverbend.
That's why there are so many wind flags at a BR shoot.
Below a shot taken at Riverbend.
SGJennings
New member
You'll find it a heck of a lot harder to hold a given MOA, say 1 MOA, group at long distance than shorter. The variables just start stacking up on you.
I agree with these guys.... short answer "yes" but in reality the groups get incrementally bigger. I picture the dispersion as "trumpet shaped" in other words the Rate Of Dispersion increases with distance. In space the dispersion would be linear, in atmosphere it's not. It gets progressively greater, progressively worse.
Now, there's a whole bunch of anecdotal data regarding rate of dispersion LESSENING with distance using certain combinations but this is a whole nuther can a' wurms and the subject of another discussion. In FACT many people end up shooting some "smaller moa groups" at 400yds than at 100 yds. In other words many people have shot say a few 3" groups at 400yds and they can regularly only shoot 1" groups at 100. When you hear talk of bullets "going to sleep" it is in reference to this phenomenon.
Al
Now, there's a whole bunch of anecdotal data regarding rate of dispersion LESSENING with distance using certain combinations but this is a whole nuther can a' wurms and the subject of another discussion. In FACT many people end up shooting some "smaller moa groups" at 400yds than at 100 yds. In other words many people have shot say a few 3" groups at 400yds and they can regularly only shoot 1" groups at 100. When you hear talk of bullets "going to sleep" it is in reference to this phenomenon.
Al
Both the U.S. Army and the NRA did testing with paper targets set up at the various distances out to 1000 yards. Each bullet fired passed through each target, so the group size could be measured. In the horizontal plane, the MOA size remained the same. I forget the year this was published in American Rifleman, but in was back in the 1940s or 1950s. Doesn't matter, the laws of physics stay pretty constant.
In the tests done, vertical did not, until someone remembered that the ammunition had a fair bit of velocity spread. It doesn't take much at 1,000 yards. Turned out that other ammunition of that lot (they couldn't measure what had already been shot!) had a velocity spread that accounted for the increased vertical dispersion, and everything fell in line.
As Al said, a bunch of guys insist that they shoot smaller at, say, 600 than 100. Believe what you chose, but the NRA and U.S. Army at the Aberdeen testing facility say "stays the same."
Obviously, the small difference that *more varying* wind imposes over longer distances affects groups size, just like the number of shots fired. But if you fire enough rounds in a test -- say 100 for good SD numbers -- the result is, in terms of MOA, distance pe se doesn't matter.
In the tests done, vertical did not, until someone remembered that the ammunition had a fair bit of velocity spread. It doesn't take much at 1,000 yards. Turned out that other ammunition of that lot (they couldn't measure what had already been shot!) had a velocity spread that accounted for the increased vertical dispersion, and everything fell in line.
As Al said, a bunch of guys insist that they shoot smaller at, say, 600 than 100. Believe what you chose, but the NRA and U.S. Army at the Aberdeen testing facility say "stays the same."
Obviously, the small difference that *more varying* wind imposes over longer distances affects groups size, just like the number of shots fired. But if you fire enough rounds in a test -- say 100 for good SD numbers -- the result is, in terms of MOA, distance pe se doesn't matter.
goodgrouper
tryingtobeabettergrouper
Simple answer: yes they do usually get bigger. But they can be smaller too, in MOA. Not in actual inch measurement. Seen it with my own eyes dozens and dozens of times with multiple guns, multiple calibers, multiple conditions. But each time, the bullet used was VLD in shape or heavy-for-caliber tangent bullets. The Aberdeen tests I read about were all done with standard ball ammo from standard twist rates decades ago.
Here's the current data Bryan Litz has shown: http://www.youtube.com/watch?v=4pF8W5liSRc&feature=channel_page
goodgrouper
tryingtobeabettergrouper
Forgot to mention, for those that don't know, Bryan Litz is an Aerospace engineer who used to work for the armed forces and is currently chief ballistician for Berger Bullets.
Pretty pictures of primary & secondary yaw damping.
How about setting up targets at multiple ranges, and firing so the bullet passes through each target. In and of itself, don't believe the damping of the yaw will affect group size. It would take varying wind.
Course I could be wrong. Nice thing about the target test is the empirical confirmation... And no, groups from different firings at different distances don't count.
JerrySharrett
Senile Member
I'd sure like to buy some of those bullets that get closer as the distance increases.
I'll also take a few thousand bullets that make the group smaller after the second shot!!!
I'll also take a few thousand bullets that make the group smaller after the second shot!!!
Wilbur, the bullet does "corkscrew" (primary and secondary yaw are sometimes summed & termed the "coning motion"). But divergence? No. There will be divergence with a change in wind (added to the other deflection) due to a different angle of attack.
Or so I understand what we are told -- both are suspect.
Edit:
Also, see Harold Vaughn, Rifle Accuracy Facts, page 221.
Or so I understand what we are told -- both are suspect.
Edit:
Also, see Harold Vaughn, Rifle Accuracy Facts, page 221.
Last edited:
MilGunsmith
Member
We have had the experiance of testing some rifles that because of a faster twist to keep the bullets stable at long range, would shoot a larger MOA group at short range. With high speed video, you can see the overspin in the bullet causing a wobble. Like a football thrown with overspin that goes to sleep as it gets further out. Shooting multiple targets at different distances all at once, will give you a ballistic track, but it is not going to give you a tru group size because the bullet is slightly deflected as it passes thru the paper. You would almost need a target as thin as toilet paper to try this.
JerrySharrett
Senile Member
From what I understand in the physics of a bullet in flight, the flight path is not a spiral, it is a somewhat algebraic curve. The bullet body does wobble/yaw on its rotational axis along that curved path, however.
Reading the hole shape in the target paper is how many top shooters troubleshoot their tune. Walt Berger suggests that a bullet that goes to sleep sooner will be less effected by the wind than a bullet that wobbles longer.
Thats it Wilbur, "goes to sleep"!!
Reading the hole shape in the target paper is how many top shooters troubleshoot their tune. Walt Berger suggests that a bullet that goes to sleep sooner will be less effected by the wind than a bullet that wobbles longer.
Thats it Wilbur, "goes to sleep"!!
No one's disputing this. That's the "coning motion" Wilbur referred to, which can also be termed primary and secondary pitch and yaw, which damps. (Usually, hopefully, both primary & secondary. Pretty much.)
& sometimes primary damps completely, but secondary only reaches an equilibrium state (gets no better, gets no worse). However, if a bullet is "dynamically unstable," as opposed to "gyroscopically unstable," the bullet can lose that equilibrium in the transonic (velocity) region, and pitch & yaw increase.
Also know as "the problem with the 168 grain Sierra International Match." (Cause of dynamic instability, for all the ballistic theory to date, is unknown. Solution is "don't use that bullet if you're interested in a target far enough away that the bullet drops below *about* 1,400 fps.")
What's being disputed is that it causes a change in group size.
To say "it must" doesn't count.
Go read the theory, both McCoy & Litz have good books on the subject. Which isn't to say they are right -- and they sometimes disagree. And who can understand all that math?
Which is why the empirical test is useful.
Maybe. I'm skeptical. Electronic targets would avoid even that possibility. Maybe they've got the money at Aberdeen? Or maybe that new Lapua 1,000 yard indoor facility in Arizona?
OK, let's make something really clear...... the cool liddle spirally visualizations that Bryan's so fond of, the ones with reference to "coning motion" and such, are wildly exaggerated computer representations of WHAT THE NOSE OF THE BULLET IS DOING.
They are NOT flight path of the bullet!
They only show that the NOSE is describing little oscillations, the TIP of the bullet. You can buy toy tops with pens mounted in the nose and draw those liddle graphs just as cool as the computer does.
Based on observation it seems that 99.9% of the populace takes from these visualizations the idea that the BULLET is kinda' "orbiting the center of it's flight path" with all sorts of football analogies mixed in when nothing could be farther from the truth. The bullet IS NOT flying like the goofy visual seems to indicate, corkscrewing it's way gently to the target.
al
They are NOT flight path of the bullet!
They only show that the NOSE is describing little oscillations, the TIP of the bullet. You can buy toy tops with pens mounted in the nose and draw those liddle graphs just as cool as the computer does.
Based on observation it seems that 99.9% of the populace takes from these visualizations the idea that the BULLET is kinda' "orbiting the center of it's flight path" with all sorts of football analogies mixed in when nothing could be farther from the truth. The bullet IS NOT flying like the goofy visual seems to indicate, corkscrewing it's way gently to the target.
al
Willllbuuur... New forum. "Things I've seemed to have seen." Preferably sober.
Actually, there have been a bunch of such posts on the long-range forum. So???
Riddle me this.
It seems the testing done by the Army & NRA doesn't count because "VLD bullets are different." Now Samuel Hall's 4-target agg record (group) is 1.6068. (600 yards). I've got a target paper somewhere where I fired 3 consecutive five shot groups, every shot counted (like a match) that aggs a flat .200 at 100 yards. That would be a 1.200 agg at 600 yards, right?
Not quite VLDs, they were 106-grain Clinch Rivers, which have a 13-caliber secant (I think) as oppose to the 15-caliber secant of a VLD as originally defined by Bill Davis. The CR's are pretty close to that.
And that's me. Guess what a really good shot could do.
Edit: to put it clearly, the agg record at 600 yards -- record, mind you -- would be .2678 at 100 yards. How many people could do that with VLDs in a bench gun? I say a lot.
Last edited: