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Very Hot Topic (More than 25 Replies) Gyroscopic Stability BP Long Range (Read 4624 times)
MartiniBelgian
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Re: Gyroscopic Stability BP Long Range
Reply #15 - Aug 31st, 2023 at 12:29pm
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The goal is to get that bullet there as efficiently as possible, which is where BC becomes important - you will have more retained velocity at the target, which will reduce your vertical.
And that is where that money bullet style shines - which actually is more or less a modern rendition of the Metford bullet (or should I say nose).  Don't forget the Brits continued LR shooting long after the discipline became more or less extinct in the US, and that Metford bullet had become the reference there.

MV isn't important, weight isn't important, time of flight and retained velocity out there is.  A better BC will also reduce wind drift.  No, it won't be a dramatic difference, but any improvement is a plus.  Especially if it means a difference between being on or off target.
  
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Schuetzendave
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Re: Gyroscopic Stability BP Long Range
Reply #16 - Aug 31st, 2023 at 3:42pm
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MV is EXTREMELY important to stabilize yaw FROM poor dynamic stability of pointier bullets where the Center of Gravity is too far back.

BC becomes toast when there is not enough velocity to stabilize the yaw.

That is why Money bullets fall asleep between 400 and 500 yards if you do not have at least 1250 fps. 
I believe TexasMac evaluated some Money bullets that were going to sleep.

Yes a good BC has less yaw and there is less wind drift. 
But if you end up with unstabilized yaw your BC gets to be significantly less.

It is not much of a problem to have sufficient velocity to stabilize the bullet's yaw (and achieve less drag) for high power shooters but becomes more of a problem for BP shooters frequently in the transonic zone when shooting long distances (1,000 yards).

If weight is not important then why have BP shooters progressed to heavier bullets to extend their long range shooting distance?

Why do drop tables show lighter bullets dropping lower at long range?

A 520 grain bullet will drop 1,655.76 inches in 1,000 yards versus only 1,578.47 inches for a 550 grain bullet (.45 caliber bullet at 1,100 fps).

But kinetic energy level relates to the distance a bullet can travel from bullet energy (in addition to just using it to evaluate bullet impact levels).

But on the other hand over stabilization of a bullet does improve the BC somewhat which is a benefit from using a tighter twist.





« Last Edit: Aug 31st, 2023 at 5:15pm by Schuetzendave »  
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CW
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Re: Gyroscopic Stability BP Long Range
Reply #17 - Aug 31st, 2023 at 9:05pm
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I think you are using "falling asleep" in a way I don't understand or have not heard it used before, or not. I understand it as the bullet settles down and flies with-out wobble. Please define. Thanks.

I have a fast twist 40-70 SS I have never been satisfied with. Shoots very well and throws one or two out. I have had the rifle almost 20 years and never considered trying it in a match. I keep trying different things and then tuck it away. This, after a truck load of powder and lead through it. It lives at the back of the safe.
Now, I am back at it again. New long bullet Cheesy 1.515" long  Grin.
  
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gunlaker
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Re: Gyroscopic Stability BP Long Range
Reply #18 - Aug 31st, 2023 at 9:26pm
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The best way to solve these debates is not on the internet of course.  It's at a long range BPTR match, 1000 yards on paper, not steel  Smiley.

Going to a bunch of these matches and shooting with some of the best, including Dave Gullo ( who is a great guy and only too happy to share his ideas ) showed me a pretty clear trend of who was winning and what they were shooting. I just copied them and it's worked pretty well Smiley

Chris.
  
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Schuetzendave
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Re: Gyroscopic Stability BP Long Range
Reply #19 - Sep 1st, 2023 at 12:25am
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"Falling asleep" had been explained to me as when the bullet drag reduces velocity to the point where the yaw point of concentricity starts to spread open until it finally wobbles. 
Or the point where the yaw is no longer stabilized over a long distance due to a decline in velocity.

I see others use it as as where the yaw point of concentricity closes with distance from the muzzle. 
Or the point where yaw becomes fully stabilized from the affects of velocity.

Appears there are different definitions for it.

So I will no longer use that term and explain the situation instead.

Chris I am not disagreeing about the success of using tight twists. 
I was trying to focus to others the need to increase velocities to stabilize certain types of bullets when you do that. 
Also to bring out discussions I had with Paul Jones that the most important factor for long range shooting  was a more balanced center of gravity of a bullet to reduce the yaw so declining velocity from drag was not as important.

But yes you can successfully use the other option of blowing more BP to increase velocities to stablize the wider yaw of pointier bullets instead of reducing the yaw by selecting a more dynamically stable bullet.

It is a benefit for some people to be aware of these options or opportunities before they invest in equipment and proceed to do their range testing.

The angle of yaw and the tightness of the cone of concentricity when the yaw is stabilized has the most effect on accuracy from wind drift.

And that is also part of the benefits of using tighter twists and heavier bullets.
Heavier bullets having a greater kinetic energy are less prone to wind drift.
But why not minimize wind drift further by selecting a better dynamically stable bullet as well?
I believe Dave Gullo has done that.
That is what the discussion is about - not about not using tight twists and heavier bullets.
And by doing so you may not need to use as much BP.
« Last Edit: Sep 1st, 2023 at 1:12am by Schuetzendave »  
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MartiniBelgian
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Re: Gyroscopic Stability BP Long Range
Reply #20 - Sep 1st, 2023 at 7:19am
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gunlaker wrote on Aug 31st, 2023 at 9:26pm:
The best way to solve these debates is not on the internet of course.  It's at a long range BPTR match, 1000 yards on paper, not steel  Smiley.

Going to a bunch of these matches and shooting with some of the best, including Dave Gullo ( who is a great guy and only too happy to share his ideas ) showed me a pretty clear trend of who was winning and what they were shooting. I just copied them and it's worked pretty well Smiley

Chris.

Exactly - if those money bullets are so inherently unstable and continuously yawing, how come they perform at long range?  And better than the older bullets that are heavier or of equal weight?  Real BC is NOT a theoretical figure, main factor determination is elevation required to get from 1 distance to another.
If there's yaw, your 'real life' BC will suffer - but apparently this doesn't seem to happen.  Well, at least not with my money bullets.  As always, the proof is in the shooting.  And W.E. Metford probably forgot during his lifetime more about BP shooting and ballistics than we will ever know.
I took a look at his ballistic tables, we still have a way to go... Or that C&H diamond grade no.6 was really powerful!
  
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Schuetzendave
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Re: Gyroscopic Stability BP Long Range
Reply #21 - Sep 1st, 2023 at 8:20am
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Yes a Money bullet with enough velocity does as about as well as a Creedmoor.

The question here is which is less susceptible to wind drift?
Is the velocity stabilized Money bullet with a bit more yaw and a slightly larger concentricity cone or the more weight balanced Creedmore with lesser yaw angle and a tighter cone of concentricity more accurate in the wind?

So how do you evaluate wind drift impacts when testing one bullet against another at the range?

I would go out on extremely windy and gusty days and shoot a number of 30 shot groups on paper with each bullet.

The large group sizes will demonstrate which is more susceptible to wind.

This process of choosing the best equipment to also minimize wind drift is how I improved my accuracy in the Schuetzen game and it also applies more so to long range shooting according to Paul Jones.

So yes do go to the range for your testing and compare bullets of the same weight that are a Money nose versus a Creedmoor versus a PJ Creedmoor where he has moved the center of gravity further forward.

And then test them for accuracy (IN THE WIND) to determine which are less susceptible to the wind.

If you are happy with your Money nose everything is great.
But some of us explore opportunities for even better accuracy which means selecting the bullet that is least susceptible to wind drift.

Long range with my .40-65 I got my Money bullet to be more accurate past 400 to 500 yards by increasing the velocity.

However I could shoot my PJ Creedmoor bullet in the .40-65 more accurately at a lower velocity (with 5 grains less BP) at long range than the Money bullet because it was less impacted by wind drift.

« Last Edit: Sep 1st, 2023 at 10:09am by Schuetzendave »  
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KaiserKong
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Re: Gyroscopic Stability BP Long Range
Reply #22 - Sep 9th, 2023 at 7:03pm
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SchuetzenDave,


Have you read McCoy’s book on external ballistics?
(You need to Login or Register to view media files and links)

I’m currently working through the mathematics and trying apply this to black powder bullets / velocities instead of more modern designs and higher Mach numbers. I’m hoping to have an answer to these types of questions too.
One point to consider - a faster twist will make a bullet with weight imbalance more susceptible to wobble too. So any gain in performance from faster twist may be negated if your mold isn’t perfectly axisymetric.
  
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MartiniBelgian
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Re: Gyroscopic Stability BP Long Range
Reply #23 - Sep 10th, 2023 at 2:50am
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True, but the difference between e.g. a 16 or 18 twist is irrelevant.   The rate of spin is such that any imbalance will show  up big time, whatever the twist.
What many fail to realize is that the money bullet xas optimized for long range, specifically reducing vertical.  This means increasing MV and a good BC  which in turn will also reduce wind drift.
So yes, this will require more powder, obviously.
  
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SchwarzStock
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Re: Gyroscopic Stability BP Long Range
Reply #24 - Sep 10th, 2023 at 7:45am
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CW wrote on Aug 31st, 2023 at 9:05pm:
I think you are using "falling asleep" in a way I don't understand or have not heard it used before, or not. I understand it as the bullet settles down and flies with-out wobble. Please define. Thanks.



My understanding as well!
  

If your rifle is not in 7.62 and you can't hit what you are aiming at with de-linked machinegun ammo you are a pretender.
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SchwarzStock
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Re: Gyroscopic Stability BP Long Range
Reply #25 - Sep 10th, 2023 at 7:48am
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gunlaker wrote on Aug 31st, 2023 at 9:26pm:
The best way to solve these debates is not on the internet of course.  It's at a long range BPTR match, 1000 yards on paper, not steel  Smiley.



Have to disagree, best proof would be through the use of a machine rest, remove the human factor.
  

If your rifle is not in 7.62 and you can't hit what you are aiming at with de-linked machinegun ammo you are a pretender.
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