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Do Bullets Go To Sleep?

 
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  #15  
Old 08-18-2013, 08:28 AM
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Re: Do Bullets Go To Sleep?

[QUOTE=Michael Courtney;839431]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.
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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
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  #16  
Old 08-26-2013, 08:40 PM
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Re: Do Bullets Go To Sleep?

Quote:
Originally Posted by Michael Courtney View Post
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.
Quote:
Originally Posted by TracySes23 View Post
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.
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  #17  
Old 08-27-2013, 12:52 PM
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Re: Do Bullets Go To Sleep?

Quote:
Originally Posted by Michael Courtney View Post
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
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  #18  
Old 08-29-2013, 01:32 PM
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Re: Do Bullets Go To Sleep?

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Originally Posted by HIN View Post
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.
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  #19  
Old 10-14-2013, 09:22 AM
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Re: Do Bullets Go To Sleep?

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?
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  #20  
Old 10-14-2013, 09:50 PM
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Re: Do Bullets Go To Sleep?

Quote:
Originally Posted by TracySes23 View Post
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.
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  #21  
Old 10-14-2013, 09:59 PM
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Join Date: Nov 2010
Location: Southern United States
Posts: 249
Re: Do Bullets Go To Sleep?

Quote:
Originally Posted by goose000 View Post
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.
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