Bullet stability vs flight time

[urcayuse]

Playing with some loads today ,just barely MOA @ 100yds. Yet they are sub 1/4 MOA at 570. Do some bullets require some flight time before they get stable? Does'nt seem to make sense but i've found this to be the result twice. Any more experienced guys out there get similar results?

[Comstar]

Originally Posted by urcayuse

,just barely MOA @ 100yds. Yet they are sub 1/4 MOA at 570.

1/4 inch at 570! Nice shooting! Lol I wish...

[elkhunter11]

1/4 inch at 570! Nice shooting! Lol I wish...

1/4moa at 570 yards, is a far cry from 1/4" at 570 yards.

[260 Rem]

If a bullet groups 1MOA AT 100yds it will produce a group of just over 5" at 500yds unless the wind blows 'em all back towards the center. Typically, only very gifted shooters with good eqpt can maintain the same accuracy at distance as they get at 100yds. One thing you can count on, is that once a bullet sets out on its path..it does not "steer" back on course! It does not "go to sleep" or get more stable. If you are getting consistent 1/4MOA groups over 500yds, you are IMO a gifted shooter.

[catnthehat]

The theory (and arguments!)of bullets going to sleep or not has been argued back and forth since arrows were invented.

I once had a Rub-ger No.1 V in .223 that drve me nutzy cuckoo.
it's 100 yard groups were no tighter than the 200 yard groups, which were respectable but not real zingers.
I talked to a couple of well known shooters about itwhich spaqarkewd the age old battle!
I then asked the old man, (who himself was a very respected ballisician within the industry) who told me to shoot ten more groups and get back to him.
Hmm, it's amazing how the avaerage of three groups can be so much different than ten groups!!
Trigger time with the rifle was the variable in that case.
YMMV

Cat

[twofifty]

quote:
"Hmm, it's amazing how the avaerage of three groups can be so much different than ten groups!!"

That there's a keeper.

[DaleJ]

Originally Posted by urcayuse

Playing with some loads today ,just barely MOA @ 100yds. Yet they are sub 1/4 MOA at 570. Do some bullets require some flight time before they get stable? Does'nt seem to make sense but i've found this to be the result twice. Any more experienced guys out there get similar results?

Makes no sense to me either, but its happened a few times. I thought it was a parallax problem until it happened again with peep sights. Bryan Litz in his Applied Ballistics book calls this the "epicyclic swerve" or corkscrew trajectory. Google epicyclic swerve and several you-tube videos will pop up. There is one that shows time of flight as well as distance traveled.

[Cal]

I've got a .223 that consistantly shoots as tight of groups at 200 yards as it does at 100, heard of such things before but I sure dont understand it.

[260 Rem]

Can't recall the exact effect of the "corkscrew" calculation, but I think it is in the neighborhood of .05" at 100YDS.... and kind of strange how that corkscrewing and sleepy bullets only surface with some rifles in spite of the fact that they are all spinning. First, shooting three shot groups can skew results dramatically. Second, a few groups do not an average make...I wish they did 'cause with some cherry picking most shooters could post some impressive stats.

[hardy]

I have an article by precision shooting that was talking about groups getting smaller at a farther distance because of the scope having a proper parallax at a farther range. Therefore the scope and rifle could actually be aimed more precisely, which in turn produces better groups. Just something else to think about.

[gitrdun]

Originally Posted by Comstar

1/4 inch at 570! Nice shooting! Lol I wish...

1/4 MOA = 1.425" @ 570 yards BTW.

Flat base bullets stabilize much faster than a boat tail at ranges up to approx. 200 yards in the. 223 rem. Boat tails take longer to stabilize but really come into stabilization at longer range where the FB bullets start to wiggle.

[urcayuse]

The hundred yard groups were 5 shot and the 570 was 3 shots, so maybe not a real fair comparison.I checked out Bergers web site and they actually mentioned that the vld's might not group all that well @100yds. I'll try some more tomorrow.

[urcayuse]

Originally Posted by DaleJ

Makes no sense to me either, but its happened a few times. I thought it was a parallax problem until it happened again with peep sights. Bryan Litz in his Applied Ballistics book calls this the "epicyclic swerve" or corkscrew trajectory. Google epicyclic swerve and several you-tube videos will pop up. There is one that shows time of flight as well as distance traveled.

Just watched the video , thats pretty cool stuff thanks

[Tactical Lever]

I read a pretty good sounding theory on it once. It being that as the bullet exits the barrel it is subjected to muzzle blast of hot gases going past it at approximately 6000 fps which temporarily destabilizes the bullet. The bullet as it is spinning, recovers and loses the wobble that may have been imparted to it. Much like a gyro-scope that has been tapped and allowed to recover.

Can't say that I have experienced it myself. Probably wouldn't notice if I did!

[260 Rem]

Originally Posted by urcayuse

The hundred yard groups were 5 shot and the 570 was 3 shots, so maybe not a real fair comparison.I checked out Bergers web site and they actually mentioned that the vld's might not group all that well @100yds. I'll try some more tomorrow.

I think Berger prefaces their comment with "some shooters have reported that VLD's do not group as well at 100yds" ... which I assume refers to some shooters experiences when compared with flat based bullets shot in short range competion. I don't think they meant the same VLD achieved better MOA group results as they got further away? I think most short range competion shooters use flat base bullets?
Further, it is my understanding that flaws on the muzzle crown will cause gasses to mess with accuracy...but, the muzzle blast from an evenly cut crown with no scratches, does not upset bullets. Could be that part of the comparison between the accuracy of flat vs. boat-tail designs have to do with the fact that it is easier to create a perfectly flat base than it is to do the same on the boat-tail?

[PoppaW]

I have a gun that shoots 4moa on paper but never misses the mark on big game. I have calculated the corkscrew effect and it is not enough to explain what I am seeing. I now use the 'cork' effect or 'shot' glass formulas. After a few calculations I don't want to go shooting anymore and it doesn't matter.

[Hotwheels81]

And here I just blamed thick crosshairs...

[duceman]

Originally Posted by PoppaW

I have a gun that shoots 4moa on paper but never misses the mark on big game. I have calculated the corkscrew effect and it is not enough to explain what I am seeing. I now use the 'cork' effect or 'shot' glass formulas. After a few calculations I don't want to go shooting anymore and it doesn't matter.

one of the best theories going! will certainly
lead to fewer gray hairs and risk of heart attack due to self induced stress.
i personally am having a way easier time realizing that some things are not in my control, or don't require my 'assistance' anyway, lee

[fish_e_o]

parallax problems???

[Tactical Lever]

Originally Posted by 260 Rem

I think Berger prefaces their comment with "some shooters have reported that VLD's do not group as well at 100yds" ... which I assume refers to some shooters experiences when compared with flat based bullets shot in short range competion. I don't think they meant the same VLD achieved better MOA group results as they got further away? I think most short range competion shooters use flat base bullets?
Further, it is my understanding that flaws on the muzzle crown will cause gasses to mess with accuracy...but, the muzzle blast from an evenly cut crown with no scratches, does not upset bullets. Could be that part of the comparison between the accuracy of flat vs. boat-tail designs have to do with the fact that it is easier to create a perfectly flat base than it is to do the same on the boat-tail?

Muzzle damage will of course affect accuracy, as will powder selection, barrel harmonics, load density, bullet to rifling contact length, twist speed, sectional density (bullet length to caliber ratio affecting rifling contact area), as well as factors I'm sure that I'm leaving out.

Damage or accuracy problems notwithstanding, all "high" velocity bullets leaving a "normal" length barrel will be passed by a jet of still expanding gases travelling at approximately mach 5. Whereupon shortly after leaving the muzzle they will be rapidly slowed (and cooled) to below bullet speed and then below speed of sound. As the gas cloud slows it creates turbulence coming from a rapid pressure change that the bullet then passes through.

This rapid pressure change and turbulence associated with it, creates a shock wave, similar to when a jet passes through sonic transitional speed, and slightly and temporarily destabilizes the bullet similar to the way a gyroscope would be if it was tapped.

Supposedly the flat base is less affected by this, which is why it is favoured for 100 yd. matches; an advantage that is lost at long range as the boat tail drifts slightly less, drops less and stays super sonic a little farther.

[Bobby B.]

Originally Posted by Tactical Lever

Muzzle damage will of course affect accuracy, as will powder selection, barrel harmonics, load density, bullet to rifling contact length, twist speed, sectional density (bullet length to caliber ratio affecting rifling contact area), as well as factors I'm sure that I'm leaving out.

Damage or accuracy problems notwithstanding, all "high" velocity bullets leaving a "normal" length barrel will be passed by a jet of still expanding gases travelling at approximately mach 5. Whereupon shortly after leaving the muzzle they will be rapidly slowed (and cooled) to below bullet speed and then below speed of sound. As the gas cloud slows it creates turbulence coming from a rapid pressure change that the bullet then passes through.

This rapid pressure change and turbulence associated with it, creates a shock wave, similar to when a jet passes through sonic transitional speed, and slightly and temporarily destabilizes the bullet similar to the way a gyroscope would be if it was tapped.

Supposedly the flat base is less affected by this, which is why it is favoured for 100 yd. matches; an advantage that is lost at long range as the boat tail drifts slightly less, drops less and stays super sonic a little farther.

This 'jet of air' has an obstacle in its path, the bullet. Therefore, this
'jet of air' cannot form itself in front of a bullet any more than a jet of water sprayed at an object can 'regroup' on the other side of the 'obstacle object'. An additional example is the beam of light from a spotlight pointed into the air being blocked by a sheet of plywood. The beam of light cannot 'form around' the plywood sheet. The obstacle blocks the path.

Bobby B.

[260 Rem]

Bobby--- makes sense to us armchair balliisticians Now, back to the idea in the OP which is that bullets can "go to sleep". As per my previous posts, I am not sold on the possibility, but perhaps a "believer" can convert me by explaining why only some bullets go sleep when fired by certain rifles? When one shooter reports improved accuracy over longer distances (say his factory Rem 700 shooting 168 SMK's from a 12:1 twist barrel are grouping 1MOA at 100yds but only 1/2MOA at 300yds) ...why doesn't that happen with every similar barrel/load combination? Perhaps a "believer" can explain, lord knows I'd like to be a convert!

[Bobby B.]

It's been years since I last discussed 'the sleeping bullet' theory and I've yet to hear a persuasive explanation detailing the concept. While it's obvious why a yawing bullet will lose its yaw and eventually stabililize, wind resistance can accomplish this, it remains difficult to believe that such stabilization somehow redirect's all bullets towards point of aim.

While I don't profess to understand all the dynamics involved in the path taken by bullets, I'm adverse to accepting falsities as fact. Theories are mostly always interesting to ponder, depending on their merit, but until logic provides clarity, conjecture is irrelevant.

Bobby B.

[Lefty]

My granddad shot lots of competitions out to 1000 yards with the 303 when I was a kid. He shot one rifle out to 400 yards and used a different one from 500 up. They were identical rifles with iron sights, but the one rifle wouldn't group very good out to 400 and he couldn't win anything with it at those distances, and it grouped way better than the other rifle after that range where he won lots. I remember lots of discussions with the other competitors about the two rifles and no one could figure out why, but they all agreed that it was fact. He's been dead now some 33 years or so, so I can't add any other information other than what I've stated. I know a lot of guys wanted to trade or buy the rifle from him but he wouldn't part with it for anything.

[Lefty-Canuck]

I have pulled out decent 0.5-1.0 inch groups @ 100 yards with my .270WIN and 1.312 inch groups @ 500 yards with the same rifle/load....sometimes my nervous twitch sets the bullet on the right path

LC

[Tactical Lever]

Originally Posted by Bobby B.

This 'jet of air' has an obstacle in its path, the bullet. Therefore, this
'jet of air' cannot form itself in front of a bullet any more than a jet of water sprayed at an object can 'regroup' on the other side of the 'obstacle object'. An additional example is the beam of light from a spotlight pointed into the air being blocked by a sheet of plywood. The beam of light cannot 'form around' the plywood sheet. The obstacle blocks the path.

Bobby B.

True, however the gases are not a laser, and are being blasted through a medium just as dense as itself. Without getting into fluid dynamics, it will not quite behave the same. The gas cloud will not act as if the bullet were not there, but it will surround the bullet and pass it. Perhaps this goes a way to explain why a boat tail seems to be affected more; as it gives more room for the gases to bypass it.

No matter how far the gas cloud travels, there will still be some turbulence.

[catnthehat]

All that stuff aside, flat based bullet jackets and bullets themselves are generally considered a lot easier to make accurate than boat tails.

Like I stated earleir, it's all voodoo, because you can get as many experts on both sides of the fence arguing that a particular bullet will or will not shoot better at 500 or 1,000 yards than it will at 50or 100.

Cat

[gopher]

Originally Posted by 260 Rem

Bobby--- makes sense to us armchair balliisticians Now, back to the idea in the OP which is that bullets can "go to sleep". As per my previous posts, I am not sold on the possibility, but perhaps a "believer" can convert me by explaining why only some bullets go sleep when fired by certain rifles? When one shooter reports improved accuracy over longer distances (say his factory Rem 700 shooting 168 SMK's from a 12:1 twist barrel are grouping 1MOA at 100yds but only 1/2MOA at 300yds) ...why doesn't that happen with every similar barrel/load combination? Perhaps a "believer" can explain, lord knows I'd like to be a convert!

The only guy to mention twist. Sierra reloading manual number 5 is a good place to look for the less informed.

[savagewsm]

Don't know if this was already posted but it is interesting to play with regarding stability.

http://www.jbmballistics.com/cgi-bin/jbmstab-5.1.cgi

In theory a bullet should have a stability factor between 1.3 and 2.0. When working up loads this program provides a decent starting point to work with.
Personally I've had good success with this.

[Bobby B.]

Originally Posted by Tactical Lever

True, however the gases are not a laser, and are being blasted through a medium just as dense as itself. Without getting into fluid dynamics, it will not quite behave the same. The gas cloud will not act as if the bullet were not there, but it will surround the bullet and pass it. Perhaps this goes a way to explain why a boat tail seems to be affected more; as it gives more room for the gases to bypass it.

No matter how far the gas cloud travels, there will still be some turbulence.

I agree that the gases are present at the base of the bullet, and present along the shank and ogive of the bullet. I also agree these gases will react upon the bullet. However, if the gases are relatively uniform in their velocity and composition as they travel alongside the bullet, their effect must be minimal and correlated to the uniformity of the bullet itself. Generally speaking, when uniform pressure is exerted, the effect is to stabilize not disrupt. In addition, the spin of the bullet must create its own insulating layer of turbulence around the bullet providing resistance to the gases as they pass the bullet. Even if the gases still generate a measurable degree of instability to the bullet, why would such a force produce a more disruptive effect on a boattail design as compared to a flatbase?

Another unknown is how the gases place themselves in front of the bullet?

Bobby B.