- Mar 6, 2008
This is a thread for discussion of the article, Do Bullets Go To Sleep?, By Michael W. Courtney, Elya R. Courtney and Amy C. Courtney. Here you can ask questions or make comments about the article.A bullet can leave the barrel with a significant yaw angle (or tip off rate leading to pitch and yaw) and then pitch and yaw in an oscillatory manner as the peak pitch and yaw angles slowly decrease as the bullet flies downrange. This paper presents an experimental design for detecting the in-flight damping and test results which support the theory of damping of pitch and yaw. Three chronographs were employed simultaneously to determine drag coefficients of bullets over near and far intervals 50 yards long for bullets fired at Mach 1.4 to Mach 3.1. Read More...
The calibration was done with the three chronographs at 10, 12, and 14 feet from the muzzle. The LED skyscreens greatly reduce the influence of changing light conditions. We've calibrated the chronographs many different times (different days, different light conditions, etc.) and we've never had them fail to meet the 0.3% specification with the LED skyscreens, and the accuracy outside is not distinctly worse than the accuracy inside.Straight up, what a fantasitic effort by the authors and researchers, especially considering the equipment employed.
First question is with regard to the calibration process. I didn't identify at which distance the calibration was done. If calibration was done at all three distances (10, 160 & 320 feet), was the difference in readings between the three chronographs still within error limits? I say this, given the tendancy of optical chronographs to be light sensative; and the light might have changed with distance(position), let alone time of day and cloud conditions.
Do you believe the spin, pitch & yaw paths to be truely circular or elipitcal as found more often in nature? If the path is more eliptical and prone to changing with velocity and distance might this impact the measured drag coeffcient each time. I'm assuming that the pitch and yaw act in combination to increase drag, but the combination would have a different effect if the pitch was at the major axis of the elipse and the yaw was only at the minor axis and vice-versa.
You may be remembering the stability papers co-authored with Don Miller where I shot the downrange chronograph. Since that event (Summer 2011), we've been much more careful. Our main upgrade in chronograph safety is having Elya or Amy behind the trigger, while I've been demoted to data recorder when we take data. Elya was the shooter for this experiment, so the chronographs were safe.Finally, were any chronographs harmed during the making of this report?
Maybe I missed the intent, but for years the alleged issue has been the supposed ability for a bullet to go to sleep and shoot much tighter at distances such as 300 yds vs 100 yds. Not one out of ten times but rather 9 out of 10 times. Never seen anyone prove a consistent sleep with tighter LR versus SR groups other than internet claims of inconsistent data at best.
So did that resolve that the issue?
First off, thanks for the article. I frequently need a push to get the gears in my head moving.
Now BountyHunter, I'm sure I don't have to tell, but smaller angular groups at longer range is most likely an issue of gyroscopic stability that may exaggerate the pitch and yawing motions, or maybe orbital gyrations? I'm not a scientist (professionally) but it seems to fit. It would be interesting to perform this test with my 75gr Amax load in a 9 twist at 2650 fps. I would think the motions would have a greater affect on drag with the much longer bullet.
As for the tighter groups at longer ranges, I will setup multiple targets out to 300yards, and shoot them all simultaneously. But, that will have to wait, because right now, they shoot great at 100 yards. I guess 90 degrees at 4300 ft is enough to properly stabilize them. When I started developing the load in 30 degree temperature, it was not. To me, that was enough evidence to confirm, but I might be fooling myself?
No keyholes, and I don't have the means to measure drag. I'm not and educated ballistitician, but I plan to run test, shooting 5 shoot groups at multiple targets placed out to 300 yards, targets lined up so they are shot simultaneously, record each shot on every target, and repeat the test as temperature changes and at different elevations.
I intend to show that as air density increases, group size of a stability "compromised" projectile can increase at short range with little affect at long range. It's not the most scientific, but it may be all the effort I am willing to put forth when the solution would be as simple as choosing a proper twist/bullet combination.
Now if I can duplicate the results?? I'll let you know. This may take a while.
Sorry about the tangent, but as for the matter at hand, why did you choose a bullet so short in length? Why not a secant BT?
No keyholes, and I don't have the means to measure drag.
I've never used a chronograph, but around 69 thru 71, my best 5 shot group was 5/16" at 100 yards with a Rem, 788 chambered for the 22-250. Never was able to do better than that, but managed a fair number of 5 shot groups under 1/2" a couple of them were 3/8".
I decided to try my luck at 200 yards hoping I could hold the same MOA. I was taken aback when my first group was 5/8". I never did better than 5/8" at 200 yards after that, but after going to the range 6-8 more times, I managed to get about 25% of my 5 shot groups just as small. i also managed to get about 45% between 3/4 - 7/8" 5 shot groups. I'm recalling from memory, but I don't think I had more than 2-3 groups go over an inch at 200 yards. The load was 35.5 gr 4064 behind a 55 grain Speer Spitzer. I know that only because, when I dug out all my reloading paraphernalia, the labels on my ammo boxes told me what load I was using.
My experience wasn't very scientific, but the MOA of the groups were so consistently better, using the same load, I could never come up with a better explanation. I have to believe something is responsible for those better groups & more consistent groups.
Unfortunately I was laid off the same year and had to move to Illinos to find a job. Never found a range close enough until recently to shoot from a bench. Two more years after that, I got divorced & was too poor to buy reloading supplies for a long time. As it is now I drive 100 miles round trip each time I want to shoot.
To top it all off, I live in Illinois, which really sucks even with the new "Concealed Carry" law that's supposed to be enacted this coming January.
If anyone has an explanation better than mine, I'd like to hear about it.
Do you accept cookies and these technologies?
Do you accept cookies and these technologies?