Do Bullets Go To Sleep?

TracySes23

Well-Known Member
Joined
Aug 16, 2012
Messages
242
Location
Champaign, IL
Anecdotal observations lile these are tantalizingly interesting.

Purusing some recent benchrest match group sizes at 100 and 200 yards shows that about 80% of the groups grow in average size (in MOA) between 100 and 200 yards, and about 20% of the groups shrink in average size. Only 10% of the groups shrink in size by an amount that can be considered statistically significant.
***************************************************
My better group sizes at 200 yards were essentially the same MOA as the 100 yard groups. However they were much more consistent. I still don't understand the lessening of flyers.

This particular range was in a valley about 75 feet deep with a flat area approximately 300 x 300 yards. There always seemed to be very little wind to deal with at ground level. I could sometimes see the leaves in the treetops moving.
Since this was the only range I'd ever shot at, I didn't realize how significant this was.

I recently purchased a new custom Savage chambered for the 22-250 with a 1 in 9 twist, Duo port action w/BR stock. I think I'm still breaking in the barrel with only 120 rounds through it so far. The wind does affect my groups consistently. I gotten several groups that were 1/2" vertical by 2" horizontal. These were 55 gr Sierra Spitzers or Hornady 60 gr HP. I've assumed the wind caused horizontal stringing. Wind is especially frustrating when trying to work up loads for a new rifle. At the age of 72, I suspect I'm not as good a shot as I used to be. So I assume a lot of blame for what I've identified as flyers, especially with vertical dispersion.

I appreciate your input. I always like a chance to view things from a different perspective or learn something that benefits my shooting or hand loading.

Spencer
 

Michael Courtney

Silver Member
Joined
Nov 15, 2010
Messages
284
Location
Southern United States
Anecdotal observations like these are tantalizingly interesting.

Perusing some recent benchrest match group sizes at 100 and 200 yards shows that about 80% of the groups grow in average size (in MOA) between 100 and 200 yards, and about 20% of the groups shrink in average size. Only 10% of the groups shrink in size by an amount that can be considered statistically significant.

When only 10% of the available data shows the shrinking group sizes with longer range, the question becomes whether this observation can be dismissed as a result of random chance, or whether it is systematically produced by some feature of the rifle barrel, bullet, and conditions. Anecdotally, we have noticed that the feature of shrinking group size seems to occur commonly for combinations that are only weakly stabilized, such as a 53-55 grain .224 bullet in a 1 in 14" twist.

Unfortunately, the available benchrest data on group sizes does not contain enough detail to analyze the data with some meaningful selection criteria that would allow assignment of a possible causal factor to the shrinking groups at longer range. To compute stabilities, we would need a record of bullet make, model, and weight, barrel twist rate, muzzle velocity, ambient temperature, humidity, and atmospheric pressure.

Consequently, we cannot yet determine whether or not the occasional occurance of smaller group sizes at longer range is a meaningful and predictable consequence of definite factors or whether it is the result of random chance.
My better group sizes at 200 yards were essentially the same MOA as the 100 yard groups. However they were much more consistent. I still don't understand the lessening of flyers.
One of the challenges in sorting out the bullet going to sleep issue is how data is actually collected and reported by different parties. Almost no two shooters treat flyers and horizontal stringing the same.

That's why I like the idea of using benchrest match data if we could get it with sufficient supplementary information about bullets, twist rates, conditions, etc.

Group sizes in benchrest matches are measured and reported with much greater uniformity of procedure.
 

TracySes23

Well-Known Member
Joined
Aug 16, 2012
Messages
242
Location
Champaign, IL
One of the challenges in sorting out the bullet going to sleep issue is how data is actually collected and reported by different parties. Almost no two shooters treat flyers and horizontal stringing the same.

That's why I like the idea of using benchrest match data if we could get it with sufficient supplementary information about bullets, twist rates, conditions, etc.

Group sizes in benchrest matches are measured and reported with much greater uniformity of procedure.
Is there someplace on the Internet where I can find this procedure?

I know how to measure extreme spread very accurately, using machined spindles with a disk near one end which positions the shaft perpendicular to the target. However I suspect there's something else I'm not considering.

Spencer
 

TracySes23

Well-Known Member
Joined
Aug 16, 2012
Messages
242
Location
Champaign, IL
Yes, if there is time . :)
Case I :When bullets are fired at velocities which are fast enough to spin them too fast they usually group less in MOA at a longer range rather a shorter one.
Case II : When bullets are fired fast enoungh to spin at the lower end of the required RPM range, groups are equal in MOA at 300 yards.
So if I'm understanding you correctly, then would a 1 in 9 twist have the tendency to shoot better at 100 yards at normal velocities or would the spin rate affect the accuracy in an adverse way? Or it's a combination of velocity & spin rate that does it?
I have 2 rifles chambered for the 22-250. A Remington 788 which is the rifle I referred to in the beginning. My second one is a Savage model 12 LRPV with the Dual Port action & AcuraTrigger which only has 120 rounds thru it to date. Since I've never knowingly broke or wore in a barrel before, I'm not sure that part is finished yet. I've done enough reading to realize all barrels don't always need the same number of shots to complete this procedure.
So I'm essentially trying to find out how to make a reasonable comparison between the two, if that's possible.
 

goose000

New Member
Joined
Oct 10, 2013
Messages
1
So how does this affect our ability to predict long range behavior based on short range models? Although it is clearly fairly simple to determine coefficients across a wide range of velocities by decreasing the powder charge and measure velocities at short ranges as you have done, you seem to have demonstrated that those coefficients do not apply to (or at least not perfectly match) down range velocity changes.
Having not read the paper on the theory, are you able to predict the dampening of coefficients with these measurements accurately enough to improve the modeling of these bullets over a long distance, and would it be possible for the hobby level enthusiast to apply these model improvements?
 

Michael Courtney

Silver Member
Joined
Nov 15, 2010
Messages
284
Location
Southern United States
So if I'm understanding you correctly, then would a 1 in 9 twist have the tendency to shoot better at 100 yards at normal velocities or would the spin rate affect the accuracy in an adverse way? Or it's a combination of velocity & spin rate that does it?
I have 2 rifles chambered for the 22-250. A Remington 788 which is the rifle I referred to in the beginning. My second one is a Savage model 12 LRPV with the Dual Port action & AcuraTrigger which only has 120 rounds thru it to date. Since I've never knowingly broke or wore in a barrel before, I'm not sure that part is finished yet. I've done enough reading to realize all barrels don't always need the same number of shots to complete this procedure.
So I'm essentially trying to find out how to make a reasonable comparison between the two, if that's possible.
There are too many confounding factors to compare the accuracy of two different barrels and ascribe the difference to any single factor such as twist rate or bullet velocity or stability or possible damping rate.

Benchrest shooters prefer to shoot the lowest twist rates that will stabilize their preferred bullet, and they also tend to pick flatbase, shorter bullets that stabilize at lower twist rates than needed to shoot the long, high BC bullets preferred by long range shooters.
 

Michael Courtney

Silver Member
Joined
Nov 15, 2010
Messages
284
Location
Southern United States
So how does this affect our ability to predict long range behavior based on short range models? Although it is clearly fairly simple to determine coefficients across a wide range of velocities by decreasing the powder charge and measure velocities at short ranges as you have done, you seem to have demonstrated that those coefficients do not apply to (or at least not perfectly match) down range velocity changes.
Having not read the paper on the theory, are you able to predict the dampening of coefficients with these measurements accurately enough to improve the modeling of these bullets over a long distance, and would it be possible for the hobby level enthusiast to apply these model improvements?
The data might be analyzed to determine typical tip off angles and damping rates for a given bullet in a given rifle, but the damping rate would only apply to a given bullet, and the tip off rate would only apply to a given rifle. A hobby level enthusiast would then need a 6 degree of freedom numerical model (like the one described by Robert McCoy and used by Bryan Litz) to apply the information.

The bigger practical effect for most hobbyists is how much BC variation there is between different rifles. Knowing the BC for a given bullet in a given rifle is probably the best improvement a hobbyist can make and much more important for predicting long range trajectories than such minutae as tip off angles and damping rates.
 

Airgunner7

Well-Known Member
Joined
Apr 4, 2010
Messages
131
Location
Boise , Idaho
I did not have time to read all of this but, If not said, I have 2 simple ways to prove concept:
1.Shoot through multiple sheets of very thin paper spaced out.
2. Shoot multiple short and long range groups with a thick rail gun or many varied loads (to eliminate harmonic grouping). The average MOA's of both close and far will be the same if bullets do not go to sleep. The key is eliminating or averaging the harmonic factor out.
Kind of funny how you always hear about developing the perfect load for a rifle but, not a distance. Some of the best 1000 yard loads shoot really bad at 200 and vice versa. My 2 cents.:)
 

TracySes23

Well-Known Member
Joined
Aug 16, 2012
Messages
242
Location
Champaign, IL
The data might be analyzed to determine typical tip off angles and damping rates for a given bullet in a given rifle, but the damping rate would only apply to a given bullet, and the tip off rate would only apply to a given rifle. A hobby level enthusiast would then need a 6 degree of freedom numerical model (like the one described by Robert McCoy and used by Bryan Litz) to apply the information.

The bigger practical effect for most hobbyists is how much BC variation there is between different rifles. Knowing the BC for a given bullet in a given rifle is probably the best improvement a hobbyist can make and much more important for predicting long range trajectories than such minutae as tip off angles and damping rates.
Now I'm really confused. Probably from my own ignorance, but why or how would the BC of a bullet change from one rifle to another?
 

Michael Courtney

Silver Member
Joined
Nov 15, 2010
Messages
284
Location
Southern United States
Now I'm really confused. Probably from my own ignorance, but why or how would the BC of a bullet change from one rifle to another?
We are experimentalists first. The fact that the BC of the same make and model of bullet, even taken from the same box, can (and often does) vary with the rifle it is fired from has been repeatedly demonstrated.

Convincing theoretical explanations are harder to come by. Different possibilities have been suggested: tip off angle, engraving, stability, velocity, obturation, etc.
 

Mikecr

Well-Known Member
Joined
Aug 10, 2003
Messages
5,308
Location
NC, oceanfront
Off axis engraving and bore/groove diameters.
Believe it or not, bullets can enter throats at angles and travel down the bore off axis. This represents a large misalignment once the bullet is released. It dampens out, but in the meantime drag is higher and nothing further will recover deceleration resulting.

Barrels are made with different bore/groove diameters for cal, and bores expand more/less depending on load and barrel contour. Bullets obturate in them to last dimension before release, which slightly affects it's form. So the bullet might release a bit shorter, and bigger than cal, or a bit longer, and smaller than cal.

This is potential for different effective BC from that finished barrel.
 

Kennibear

Well-Known Member
Joined
Jul 24, 2012
Messages
493
Location
Washington State
WOW!!!

Ohler makes an acoustical target that works only on supersonic bullets. I do not know if it can distinguish to the finesse required for this. It could be set up to record the accuracy at multiple ranges of the bullet's path. As soon as the bullet strikes a solid target, no matter how thin, the bullet will be deflected. You cannot meaningfully shoot through multiple solid targets,even very ethereal ones, for accuracy comparisons.

Unless I am visualizing this wrong, the assumption is the wobble of the bullet is damped out at some undetermined range and continues on its merry way at the lowest Cd of that particular shot. That is; at some point the bullet settles into its best low drag configuration. Correct?

In the world according to Kennibear here are my assumptions:
1) The bullets are traveling along a theoretical average path.
2) Wobble (Redneck for yaw and pitch) cause bullets to diverge from said theoretical path.
3) Yaw diverts the bullets in one plane in two possible directions and pitch diverts the bullets in a perpendicular plane to yaw in two possible directions.
4) There are no "perfect" shots and each individual shot will wobble somewhat.
5) Wobbles are snowflakes, no two the same.
6) Each shot will enter an actual bullet path divergent from the theoretical consistent with its wobble and stabilize in a path (Cease Divergence) at the point where the bullet goes to sleep.
7) From the bullet's "nappy time" place along its path it will continue at that divergent axial value from the theoretical until impact.
Conclusion:
When we shoot a group of say five bullets they will diverge (i.e. accuracy will suffer) until they "go to sleep". I doubt "nappy time" is at the same place in the path for every bullet. But from that point they will each travel along a path at relatively fixed distance from the theoretical. Therefore we would observe the MOA group size increase until "nappy time" is reached and the actual measurement of the group (in inches) remains fixed as the range increases which appears as decreasing MOA. Unless the divergence of the path imposed by the wobble includes a significant angular component, at which point the accuracy looks like every group my poor eyesight and caffeine hammered nerves have ever shot.

Just the odd ramblings of an old Idaho coffee drinker......
 

Mikecr

Well-Known Member
Joined
Aug 10, 2003
Messages
5,308
Location
NC, oceanfront
No, the moments normally dampen very quickly, like before exiting the chronograph. There may be a minimal bit(very little) nearing 100yds that would likely continue due to it's cause by then.
Dynamic issues/dynamic instability is another matter. This can grow & grow downrange. Neither will shrink grouping.

There is so far zero ballistic evidence supporting shrinking grouping with distance.
Where it's observed, and I've seen it and could reproduce it, it wasn't because of elliptical swerve.
It was likely scope parallax settings different up close -vs- distant.
I'm someone who shoots better moa at distance. I've never been able to shoot better in moa at 100-200yds, than 300-500yds, and it applies to all my guns. But, I'm always using the same scopes(Mk4, NXS), and I think this is my issue(that doesn't hurt anything).
It's difficult to set focus up close(100yds), where you're expecting best performance. Here, you can move the side focus quite a bit each way & your brain will adjust(compensate) to seem focused still.
In Contrast, it's very easy to set focus at distance(500yds), as you're either dead on it or it's obviously not. Too difficult for your brain to compensate this disparity.
 

Kennibear

Well-Known Member
Joined
Jul 24, 2012
Messages
493
Location
Washington State
MikeCr

Thanks for your response. It only raises a couple more questions:

1) Inferred in your response is the dampening of the wobble does not practically effect the LR hunter. But most of us have practical experience with ammo loaded with the bullets eccentrically off, i.e. bullet not straight in the case or with the bore (bent case neck). You are saying that the bullet "going to sleep" does not apply to sloppy bullet fit and we cannot count on that effect improving said ammo @ long range?

2) Does the change in Cd affect the BC of our bullets enough to increase the uncertainty (or create a variable) BC that compromises the predictability of the bullets path? Are our computer ballistics programs going to have a margin of error large enough to limit their accuracy for our purpose because of this?

3) Why not Cd instead of BC? Is the tide of Ballistics Research so ingrained in Ingall's original mathematical theories that we cannot change? Aerodynamics uses Cd and not a coefficient that adjusts the airfoil performance to match some arbitrary standard (G1/G7). The wind tunnel data generates a data curve (a data cloud really) across a range of Reynolds Numbers (think different velocities at different altitudes) and performance predictions are based on that. Our mathematics have always bugged me because we use BC's for maybe three ranges and none are accurate at correcting for form factor (to 1/10th of 1%) and so on and so forth. Cd seems a cleaner albeit mathematically more extensive solution. But we have computers today.

I'd better stop here or otherwise I'm going to have to type this up and submit it as a term paper.....

Thanks!

KB
 

Trending threads

Recent Posts

Top