Spin and stability
- Thread starter max-x
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How to explain this better?
If we talk about it in terms of statistics around the BC: benchrest shooters and F-class shooters are looking for a small standard deviation in BC values (or any dimension or weight). If the average changes, it isn't a big deal for them because their sighters allow them to adjust for the change in POI that will cause. We don't need as small of a standard deviation in BC values. We can tolerate a larger SD, what we can't tolerate is the average moving on us.
This BR shooter could not care less about BC's.
I would have thought after all these posts where you argued that you needed predictable and stable BC's due to your lack of sighters and frequent need to calculate firing solutions beyond 1000 yards, and this is surprising, you now say you can tolerate a larger SD in BC's than in F Class or BR, but don't want the average BC to move around. Averages can be filled with extreme values, don't argue that you want averages that don't move. That will take some explaining as it goes against all your other posts above.
For what you want to do, you need the lowest possible SD of BC for any discipline you care to name, and the lowest possible extreme spread of BC for any discipline you care to name. Forget the average.
Which brings us full circle to the bullet itself. Is it up to the task you think it is, or is it prone to a lot of manufacturing defects or compromises that will limit it's ability to meet your expectations? Not every bad shot is the shooter or the wind or the gun. Sometimes it is the bullet itself. I am saying keep an open mind.
Look at muzzle velocity. F-class isn't as concerned with the actual number, as long as there is the least amount of vertical on the paper.
PRS also want the least amount of vertical, but also need to know the precise value for their calculators.
SD of the BC = extreme spread of MV
average BC = average MV
How many F-class shooters have ultra precise chronographs vs how many PRS shooters do? I'd bet the PRS have more.
Why do you keep going back to bullet quality? Do you have bullets to sell? What are their specs and cost?
Let's say I buy your high quality bullet that is better up to the task than the mass produced offering. Is it's BC not going to drop off when the SG drops below 1.5 as every bullet did in Bryan's tests?
Not interested in selling bullets it is a thankless task.
Of course the BC will drop with a SG less than 1.5 but if you want to argue that quality bullets aren't useful on that basis, you and I will never see the problem in a similar way. BC is only an archaic measure of observed performance, it does not necessarily make it a good bullet.
Mystic Precision
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A few thoughts to consider...
How do you maintain very small vertical (sub 1/2 min) at 1000yds if not to have VERY CONSISTENT velocity AND drop? How do you have very consistent drop if the BC is varying?
How do you know that you are able to shoot very tight LR vertical if not to measure with very precise chronographs?
How do you improve the odds of converting your sighters if you don't have a very stable and reliable set up over a wide range of ambient conditions? At the top levels of F class, we all want to have 17shots to score 15... those sighters matter so they aren't treated as random shots.
Except for the errors in wind judgement, those sighters are aimed to hit a 1/2 MOA circle at the furthest distances competed. How can you do this if you have no idea where that shot is going to go?
I had a nice chuckle with some of the PRS vs F class comments. What PRS shooters want in bullet placement is what F'ers spend enormous efforts to perfect.
If consistent BC is the goal, then consider that RPM has a profound effect of the flight characteristics of every bullet.... the effect is not constant for all bullet shapes.
And this affect can change with flight speed.
Until you start testing at the furthest distances you are competing at, you are only assuming that the results you calculate at short range is what you are going to get at long.
There are a growing number of shooters who are seeing results unique to certain bullets and bullet designs which are contrary to the designers suggestions.
A big reason some bullets made of the "best" technology are being quietly modified and adjusted.... why I have suggested continued testing and observation.
Jerry
How do you maintain very small vertical (sub 1/2 min) at 1000yds if not to have VERY CONSISTENT velocity AND drop? How do you have very consistent drop if the BC is varying?
How do you know that you are able to shoot very tight LR vertical if not to measure with very precise chronographs?
How do you improve the odds of converting your sighters if you don't have a very stable and reliable set up over a wide range of ambient conditions? At the top levels of F class, we all want to have 17shots to score 15... those sighters matter so they aren't treated as random shots.
Except for the errors in wind judgement, those sighters are aimed to hit a 1/2 MOA circle at the furthest distances competed. How can you do this if you have no idea where that shot is going to go?
I had a nice chuckle with some of the PRS vs F class comments. What PRS shooters want in bullet placement is what F'ers spend enormous efforts to perfect.
If consistent BC is the goal, then consider that RPM has a profound effect of the flight characteristics of every bullet.... the effect is not constant for all bullet shapes.
And this affect can change with flight speed.
Until you start testing at the furthest distances you are competing at, you are only assuming that the results you calculate at short range is what you are going to get at long.
There are a growing number of shooters who are seeing results unique to certain bullets and bullet designs which are contrary to the designers suggestions.
A big reason some bullets made of the "best" technology are being quietly modified and adjusted.... why I have suggested continued testing and observation.
Jerry
I was never arguing that quality bullets aren't better, only that one should choose a twist rate that keeps SG above 1.5 in the temperatures they plan to shoot in if they need to rely on that number not changing on them when the temperature changes. Regardless of bullet quality, I will choose a twist that keeps SG above 1.5 for the temperatures I want to shoot in. A slower twist may yield slightly tighter groups, but the BC changing with temperature causes me more heartburn. An accurate BC is critical for calculating an accurate trajectory. That doesn't change with bullet quality. The higher quality bullet will have a more consistent trajectory, but you still need to know it's BC in order to calculate the trajectory accurately.
Maybe by looking at the holes in the paper? Isn't that what you are always saying? If you have a very precise chronograph, why not shoot your ladder tests at 100yds?
How many F-class shooter use a ballistic calculator? Barely any I'd bet. I don't. We just dial in what we used the day before and add a click or two if it's a bit warmer.
F-class wants consistency, first and foremost. Each round the exact same as the last one. PRS also needs the same consistency, but they also need predictability.
Take two bullets. Equal BC for both of them. Bullet A is perfect in all aspects. Bullet B is the same but has one parameter that varies quite a bit. Let's say some rounds have a centre of gravity a bit too far forward. Manufacturing defect.
Run the numbers in your app, dial and shoot. Bullet A hit the target, nice group. "Lower quality" bullet B also hits the target, but has a larger group.
I guess you win. Now you are arguing against using quality bullets since it apparently has no merit in calculating trajectory over a lesser quality bullet. Why not shoot Speers then? I really don't understand why this is so tough.
It would actually help you tremendously to calculate trajectory if you knew the bullet could be counted on time and time again to do exactly what you want it to do. Or you can try and figure why you missed when your iPhone said your trajectory was perfect and you still missed. Maybe it was the bullet failing to deliver the goods? It happens all the time but most will blame every other component in the system before they blame the bullet. The bullet doesn't care about your iphone.
coleman1495
CGN Ultra frequent flyer
- Location
- Whitecourt
Ouch jeez that one kind of hurt. Okay granted I never worked at putting rockets into space, I do take pride in being a some what analytical person. Its true that the people that did these experiments put a lot more into it. There is a lot of experimentation that goes into putting something on Mars.
I am not sure I understand exactly what the debate is about here. The BC does change during the bullets flight path. There are a number of variables that go into that.
Lets say someone tested a rifle extensively at 300 yds. They calculated drop, BC and everything they possibly could. Would they be able to determined the where the flight path at lets say 1000yds?
Really?
Have you read "Rifle Accuracy Facts"
Do you realize all gathered data, observations and suggested conclusions were compiled to reveal why some factory rifles shoot more accurately than others?
Do you realize none of his data sets or observations ended with "IMO" or "YMMV" or "just keep an open mind"
The fact he used a 270 and lead tipped bullets is irrelevant as he was not studying down range bullet performance or inherent cartridge accuracy potential. He used a rifle as a constant control marker and made various changes to the platform to rest various hypothesis. Whether the test rifle is a 270, 30-06 or 300Win, the principles of chambering, lug alignment, bolt alignment, thread design, bedding and ammunition run-out remain the same and can be applied to the science of rifle accuracy or precision in all disciplines.
He also used a 6mmBR rail gun in his testing - he was well aware of the accuracy potential of various rifle platforms and cartridge design.
The book covers:
1 Internal Ballistics,
2 Chamber and throat Design,
3 Barrel Vibration,
4 Scope and Sight problems,
5 Barrel Receiver Thread Joint Motion,
6 Muzzle Blast,
7 Bullet Core Problems,
8 Bullet Imbalance,
9 External Ballistics etc.... ALL of these are common potential variables in any rifle system.
"widely discredited".............really?
-Precision Shooting Magazine re-published his book in 1998
-6mmBR lists it as a top resource http://www.6mmbr.com/bookreviews.html
-it is a recommended resource on Gradous Rifles site: http://www.gradousrifles.com/links.php
One weak criticism surrounds Harold's assertion of barrel torque on the action interface. Because the bench-rest community uses very little torque when installing a barrel, Harold's conclusions were deemed invalid. What most do not realize who have not read the book is that the torque/force of tightening the barrel to the action has nothing to do with creating more pressure between the square interface between the barrel and action. If the book is read and understood, it makes perfect sense...... Ask Robert Gradous or Greg Tannel, or, any of the top Smiths in the US of which these guys have personally assisted over the years. There are more than you can imagine!
The point is that the top scientific minds who have chosen an interest in precision shooting have much to offer this industry.
I have yet to see anyone discredit or even come close to amassing any contradictory data to oppose the wealth of information that Bryan Litz has built.
This debate is ridiculous
DO we see arguments like this on 6mmbr.com? ....No, they appreciate Brian Litz' work and are pleased to have the knowledge passed along for free.
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Got Juice?
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- Peoples Republik of Kanukkistan
The faster the rotation, the more stable the bullet will be. However when the C of pressure changes on the bullet in the transonic region of flight, there is a slight yaw induced from gravity acting on the bullet, which will in turn cause more yaw until the bullet starts tumbling uncontrollably.
I think that is how it goes. I'd have to look back in my notes on projectile motion.
I think that is how it goes. I'd have to look back in my notes on projectile motion.
Got Juice?
CGN Ultra frequent flyer
- Location
- Peoples Republik of Kanukkistan
Ahh, the old 'precision' vs 'accuracy' debate love it.
rpollock, I think that your assertions on the importance of bullet quality are correct. A poorly manufactured bullet, with inconsistencies in aligning all the various centers of gravity longitudinally with the center of rotation will absolutely cause both loss in accuracy and BC. Why is this? At the risk of being torn to shreds for heresy on this thread, I'll try to relate the scenario to an easily discernable similar scenario, take a thrown football- a good bullet pass shows good stability and minimum drag. A poorly thrown (underspun) ball, may fly well, or may fly with a wobble. If it has a wobble, what is occurring? Well, each time the frontal surface area of the ball increases due to the divergence of the longitudinal axis from the axis of rotation, small additions in form drag occur, hence, changing it's 'BC'. While I have no way to empirically prove exact correlation, I would expect that this reason is similar to why an underspun bullet shows a reduction in effective BC. To further expand on the benefit of using quality bullets, in addition to being underspun, a properly spun poorly manufactured bullet with a longitudinal CG which is misaligned with the center of rotation, would also experience a wobble, which may impart minor cycles of yaw, like the football, and which would reduce observed BC. The BC of the bullet itself hasn't particularly changed much, but it's flight characteristics have caused the observations to diverge from the math. A corollary to this would be that in the supersonic regime, the forward shock imparts lift to the body when an angle of attack is created, and it's effect is greater than that of air resistance at subsonic speeds. This may cause a random divergence of what becomes printed on paper.
The next thought, returning to the original topic of SG is: might there be any merit in overspinning a poorer quality bullet- like the dreaded Amax, in order to minimize the effects of the above described scenario. I believe that this is what Litz observes in his first book in the epicyclic swerve page.
Thereafter, how would this attempt balance with paying the price of now needing to manage more resultant torque during the firing cycle?
The next thought, returning to the original topic of SG is: might there be any merit in overspinning a poorer quality bullet- like the dreaded Amax, in order to minimize the effects of the above described scenario. I believe that this is what Litz observes in his first book in the epicyclic swerve page.
Thereafter, how would this attempt balance with paying the price of now needing to manage more resultant torque during the firing cycle?
