Better Groups At Distance

[Tiny Tim]

The arrow definitely doesn't seem to follow the line of sight or a straight line. The arrow comes out of the bow moving in the direction of the target at a slight angle. The angle steers the arrow off of the main path until it straightens out and then the main direction carries the arrow to target. It seems like I can see it isn't a straight line. Getting the arrow out of the bow straight definitely reduces group size on the target. The arrow is only tilted for say 10yds before the vanes pull it straight. I tune my bow to shoot a bare shaft arrow reasonably well at 25yds because it magnifies the impact at the target and allows me to tweak the tuning. I don't need to tune further out because the impact is all in at say 10yds and backing up further just adds other factors that I am not trying to tune. Once get the arrow launching straight I can add a broadhead and shoot an arrow with vanes from as far away as 90yds on a good day without any wind.

Is there any basis for thinking a bullet could do something similar. Launch tilted and slide until it stabilizes? If launched tilted would it slide because of aero jump where the bullet is tilted relative to the air vector? Tilted in the bore seems like a random effect because it would be tilted and spinning or wobbling. Tilted as it exits the bore could be spinning on a tilted axis. If the tilt was somewhat consistent the impact at the target could be regular and limited to a fixed displacement that does not vary with distance. Let's say the tilt alone creates a 0.5in variation in POI at 100yds but it does not persist beyond 100yds because the bullet stabilized. Then lets say the variation in angle launched created another 0.5in variation in POI at 100yds but it persists beyond 100yds. The measured group might be as large as 1in or 1MOA. At 200yds the tilt still only caused 0.5in or 0.25MOA. The angle launched is still 0.5MOA so perhaps we see a 0.75MOA group. At 400yds we are down to 0.625MOA assuming other factors don't start to creep in. The shrinking in group size would only appear in certain conditions.

Again, all just a giant what if! Good chance it is all just ******** because nobody has proven it in a shoot through situation. I just keep thinking about it in the context of my bow.

Your right in that we don't know exactly. My point was simply that archers paradox could in theory produce a similar result but there would be evidence (tear high, low, left, or right). But if the arrow is weak or stiff, the poi is off and increases with distance. Just a good analogy to help me think outside the box a little.

 

[David_h]

One variable to consider is scope magnification. Try reducing magnification at shorter distances to same ratio as at longer distances.

 

[chav0_12]

You guys are missing a huge difference comparing bullets to arrows. One is fin-stabilized and the other is spin. They act completely different in their stability due to this fact. A bullet isn't going to spin more to become more stable once it leaves the bore, just like velocity, that rate only slows down. A fin-stabilized projectile on the other hand will become more stable as it settles from the initial thrust and the fins take over to stabilize it. Similarly to spin-stabilization, as a fin stabilized projectile loses enough velocity, it will also lose stability.

 

[Critter Picker]

What he said ^^^^^ the faster an arrow flies and the more offset the vanes (or feathers) have, the faster it spins. If you have ever seen an arrow leave a bow in slow motion it looks similar to a fish swimming. It actually wraps around the riser.

 

[ericbc7]

So what you are describing is impossible from a physics standpoint. The bullet never pulls itself back into the line of sight once it deviates. I've heard this described as the bullet is going to sleep or some such nonsense. Windage could explain only but half of the group as bullets shot further to the other side would be pushed out of the group the same amount. What I believe explains it is that at 100 yards, the shooter focuses too much on the small center of the target. That's why you see larger deviations. When the target is at distance, the shooter has a much less detailed target to focus on and is less likely to try to make last minute adjustments in rifle movement before pulling the trigger. Given my anecdotal experience with it, I'd say this explanation is more likely.

View attachment 457682

This is easy to demonstrate now with the advent of shot marker systems that can be set up in series.

 

[Mikecr]

A bullet isn't going to spin more to become more stable once it leaves the bore, just like velocity, that rate only slows down.

Gyroscopic stability normally goes up (considerably) as a bullet travels downrange. Then drops again through transonic.
But I agree that drag stability, moving center of pressure behind center of mass, is different from gyroscopic stability.

 

[Tiny Tim]

A bullet isn't going to spin more to become more stable once it leaves the bore, just like velocity, that rate only slows down. A fin-stabilized projectile on the other hand will become more stable as it settles from the initial thrust and the fins take over to stabilize it. Similarly to spin-stabilization, as a fin stabilized projectile loses enough velocity, it will also lose stability.

Yes, as velocity falls to a certain point, both will destabilize. And while a bullet does not increase its spin rate, it does become more stable (like the arrow), because the rate of spin decay is less than the rate of speed decay.

 

[Maol]

tankgijohn72 in post #28 offers the proof why nobody has ever collected Bryan's $1,000. The effect isn't Ballistic. When it is observed it has to have another cause besides gun effects on the projectile.

IMO the most likely cause is optical, either eye or scope, or the shooter's focus.

 

[Mikecr]

When terms like 'impossible', or 'physics', or 'proof' are cast, it sabotages the search for truths.
One scenario is not proof of all.
A common notion means nothing of possible.
And physics in this matter is far broader than considered with highly limited shoot through testing.

So while this alludes us, soft opinions are actually more valuable to consider than rigid declarations.
Personally, I'd like the answer, and could care less about results of a $1,000 publicity stunt.

 

[D-mon]

So we could explain the phenomenon of the bullet being more accurate at longer range by:
1: being more focused at the longer distance .
or 2: the bullet going to sleep ( although it seems that Brian litz has debunked that one.)
but what about positive compensation ?
when you look at how rimfire bench rest shooters are using tuners to titghten their group, it is some sort of positive compensation so that the slowest bullet and the fastest bullet launched at two separate departing angles, do meet at the same spot at a given distance. I do not know if a rimfire bench gun could have its tuner retuned for another given distance like 100 or 200 yards. but that would be an interesting experiment.
At least the positive compensation seems to be working on the vertical plan.
i have also read the following article that made me think about it:

Using barrel vibrations to tune a barrel

www.geoffrey-kolbe.com

 

[Radman]

I have been searching for a rational reason that bullets wouldn't maintain a constant angular deviation between POA and POI as they travel down range. In other words, how could groups at say 600yds be smaller MOA than groups at 100yds?

Initial, it doesn't make sense that a bullet could improve the MOA over distance. It starts at the muzzle and passes through the hole in the target 1MOA off of POA at 100yds. It has to stay on that line and be 1MOA or more at 600yds!

Yet, many folks state that is exactly what happens and I believe that is what they are seeing. They say their 600yd group is better than their 100yd group. They see 1 MOA at 100yds and 0.5MOA at 600yds. I have seen it explained as it simply takes time for the bullet to "stabilize".

Aerodynamic jump seems to explain this if we assume the jump or slide is caused any time the bullet axis isn't aligned with the air. A cross wind causes the bullet to turn very slightly into the wind any the gyro effect causes the bullet to slide up or down as long as the cross wind is present. A constant wind results in a constant slide that shows up as a constant MOA angle.

If a bullet gets tilted for some other reason then there would be a slide as long as there was a tilt. The bullet could engage the rifling and travel down the barrel slightly tilted. The bullet could be knock silly as it exists the barrel and gas escapes around it. Eventually, the bullet would align and the slide would stop or the bullet would "stabilize". In other words, once the force that caused the tilt is removed the bullet wants to stabilize and stop sliding and just travel along the line in which it was launched.

This seems to explain how groups could get smaller. Each bullet follows a path that is somewhat colinear, however the lines are slightly offset because of the slide. The slide is a finite change in POI that does not continue to increase after the bullet stabilizes because the slide stops. If the slide is 3/8" at 100yd it might still be 3/8" at 600yds.

Layered on top of that we have the whip of the barrel which changes the POI and causes small changes in angle that would be constant for each bullet after it leaves the barrel. 1 MOA at 100yds would remain 1 MOA at 600yds. The observed performance at 600yds would be primarily driven by changes in angle at the time the bullet leaves the muzzle.

It seems like we are tuning loads to minimize both effects. We want to get the bullet out of the barrel while it is pointed in the same direction for the longest period of time. Then we want to minimize the time it takes the bullet to stabilize and stop sliding. If you get the timing right the changes in exit timing will have a minimal impact. Perhaps adjusting seating depth minimizes the tilt and time needed for the bullet to stabilize?

I buy what you're saying. May play into some of Craig Boddingtons articles. I also believe that your 4th & 5th paragraph may explain why occasionally someone may get a flyer from a perfect rifle. JMO

 

[Mike Matteson]

Concentration definitely helps...of which I lack at 100yds....but back at 400yd I'm less than moa..sometimes 1/2moa...
Depends on bullets and speed too I believe.....as some say above 2950fps can blow tips off of noslers LRABs...
..can't be positive..but I've never recovered a LRAB with a tip on it...........

Dam you mean the tip aren't on it after firing it. I am just joking!
I can't really say that the bullet is more stablilizes at greater ranges than 100yds. Now long ranger for me is generally 500yds. By these days standards that isn't much in distances.
I what I did find in shooting those distance was. My groups at 100yds were in the range of 1/2", and at 500yds were about 3". I never noted smaller groups at longer ranges. They seem to be consistent in group growing at the different distances going out to 500yds.
I am not say that, that can't happen, but it doesn't seem total correct that it would take place.
This summer I think I will get a chance to see what happens at those distances and at longer ranges.
It will be interesting to say the least.

 

[Mikecr]

when you look at how rimfire bench rest shooters are using tuners to titghten their group, it is some sort of positive compensation so that the slowest bullet and the fastest bullet launched at two separate departing angles, do meet at the same spot at a given distance.

Yes, rimfire shooters use tuners because they cannot adjust their loads.
The 2 attributes of tune that are separate and totally different are powder tune & barrel tune.
A tuner does not affect powder tune, but barrel tune.
You absolutely can tweak these attributes, separately, to optimize a specific range.
So logically, you could do this to mess up a specific range.

This is why I suspect that you could dial in at 500yds -while messing up 250yd grouping.
Nobody would do that on purpose, but I think it could happen.

 

[Maol]

When terms like 'impossible', or 'physics', or 'proof' are cast, it sabotages the search for truths.
One scenario is not proof of all.
A common notion means nothing of possible.
And physics in this matter is far broader than considered with highly limited shoot through testing.

So while this alludes us, soft opinions are actually more valuable to consider than rigid declarations.
Personally, I'd like the answer, and could care less about results of a $1,000 publicity stunt.

The search for truths requires sifting the possible from the impossible, and theories need to be proved. If physics isn't the measure what should we use?

tankgijohn72 in post #28 gives first order evidence stating in his lab testing it never happened. That the physics we all use to develop dope were solid, and that the 100 yard 'hit' predicted the 300 yard POI, 100% of the time, without fail.

I am not saying the effect isn't real. Only that Bryan Litz Chief Ballistician for Berger Bullets, and arguably the top external ballistics expert in the US, maybe the world, and tankgijohn72 an engineer that oversaw the exact tests that would determine if it was ballistic have stated it wasn't. My own theory was that it was ballistic, in fact I believed that it was instability. I have actually posted elsewhere espousing that very theory, and have believed it was so, right up until empirical evidence proved it wasn't true.

To many folks I respect have stated that they have seen the phenomena to discount it as a will-o-wisp, mirage or delusion. But, because it must be IMO either optical in nature, or have to do with the shooter got me thinking. Those thoughts about this, brought back to the fore something from the dusty and murky past.

Some here are old enough to remember when the cult classic: Secrets of the Houston Warehouse – Lessons In Extreme Rifle Accuracy an article was originally published in Precision Shooting Magazine Special Edition #1 1993 first came out. Well worth hanging on to it is downloadable here.

BTW I too want to get to the bottom of it, there is something to it and worth knowing.