Borderline Stabilization... at long range [Archive]

Eutectic

10-09-2010, 02:27 PM

I hear comments on this forum all the time about slower rifling twists for cast bullets... Let's call them 'Borderline Twists'... It is an old philosophy with cast bullets, and many 'old masters', even Harry Pope, believed this way.

We have quite a few 'new masters' on this forum. I say this honestly and truthfully and I would ask all readers to please not let my direct nature of communication to come across the wrong way..... A certain 'opinion' come up here all the time it seems. An opinion I disagree with... An opinion, that for years, has proven opposite for me; many of my experiences supporting this! Truthfully my goal here is to find out if I have been wrong all these years. My goal is to find out WHY my findings are different. A discussion of why your opinion may be different than my findings......

The 'opinion' I would like to discuss usually reads something like this:

"If 300 yards is the maximum distance you intend to shoot this bullet and twist, and the boolit remains point on and accurate at that distance then your twist is fast enough."

Usually, if not always, the load/twist combination has been already shot at a closer distance, say like 100 yards.

My first question: "Why is stability less at 300 yards than at 100 yards?"

Perhaps the best way to get answers is to write down how I see it and why. Then I'll let your expertise show me if, where, when I went wrong.

In the 40's I got an old trapdoor Springfield. Black powder was fairly uncommon at that time period with few using it. But my father had me loading 70grs of Hercules Fg behind Lyman's #457125. Boy, they kicked! At 50 or 100 yards the bullet holes were oval. Not keyholes... just oval. I learned to call this yaw... The barrel was decent and the twist is 1 in 22" I believe.. I figured if they were bad at 100 yards, they must really get bad out at 300, 500 yards. So I asked my father...

"Nope..... they'll get better way out there. The bullet has time 'to go to sleep'."

I would not forget his comment 'go to sleep'....... But what is it?????

A current thread talks about 120gr RCBS gaschecked boolits in the .250 Savage with poor results.... So let me choose the ol' .250 Savage in a hypothetical situation if I may....

We have an older .250-3000 with a 1 in 14" twist. We have a Lyman #257325 bullet mold that casts a .25-35 round nose boolit at about 112grs. We finally work up a load at 2000fps muzzle velocity that shoots OK, but the bullet holes display 'yaw' at the 100 yard target.... Wow! I wonder what would happen at 300 yards? I wonder what would happen at 530 yards???

Why 530 yards? I hear someone saying....... I'll answer that. The retaining velocity at 530 yards is 1000fps or 50% of our muzzle velocity.

RPM's..... Several here talk a lot about boolit RPM's... Let me put a little different 'spin' (sorry) on RPM......

If we calculate 2000fps in a 14" twist I get 102,857 RPM at the muzzle....

If we calculate 1000fps in a 14" twist I get 51,429 RPM...

Is this the correct RPM at 530 yards for our example load above then?

The boolit in our example load above leaves the muzzle of our rifle 'locked in' at departure turning one 360 degree revolution in 14" of travel.

OK... A tougher question.... At 530 yards does our bullet still travel 14" to make one full (360 degree) revolution?

I believe most believe this twist distance is always 'locked' in as it is at the moment the boolit leaves the rifling....

I say NO!!!! I'll say that we experience a downrange phenomena I'll coin a 'compressed helix'.!!!! I'll say that rotational spin and forward travel become independent of each other at departure from the muzzle; each having their own set of variables!!...

Noted Ballisticians have made comments that gyroscopic or rotational speed slows down much less than our boolit's forward travel fighting air resistance head-on. Some Ballisticians say RPM slows very little... I agree with this but cannot prove it. But in our hypothetical example above lets pick a generous amount of rotational, or RPM lost... Let's say we lose 20% of our RPM over 530 yards or more easily looked at we have 80% of our original RPM that we had at the muzzle. That figure is 82,286 RPM. I think it could be higher... we are only talking 1.175 second of flight time here.

So if you allow me the 82,286 RPM figure and we calculate this against our 530 yard retaining velocity of 1000fps to get a theoretical 'twist' for these numbers the twist would then be the equivalent of 1 turn in 8 7/8" for our boolit!!!!!

This is 'going to sleep' !...... This is a 'compressed helix'.....

I say a borderline stabilized at departure boolit (balanced - with no flaws) becomes more stable, not less stable, at longer ranges!

Where have I gone wrong gentlemen?

Eutectic

Good Cheer

10-09-2010, 03:48 PM

For what it's worth.
My grandfather was trained as a sniper on Long Island prior to going to France in 1918. The German officers acting as instructors explained to him that the bullets scribed an ever changing increasingly larger spiral through the air on their way down range. And, that this was why the bullet drop was in part negated by rise at long range. The energy it takes to create that curve ball type alteration of trajectory must have been lost from the slug as the rifling marks interacted with the atmosphere; i.e., the spin rpm must have decreased...some.
I do not remember how far they were shooting.

Fixxah

10-09-2010, 03:50 PM

Interesting read. I can buy the whole theory.

leftiye

10-09-2010, 03:56 PM

Depends on how severe the instability is.

Thas (opening spiral) because of air resistance acting against an unstable boolit as the bullet spins. Uneven air resistance against the canted (yawing) boolit planes the boolit and as it rotates this becomes a spiral.

Deflected boolits as in when they have hit a branch fly in an exaggerated cone, spiraling around the outside of the cone.

Uneven air resistance against the canted bullet causes some bullets to stabilize over a (short) time, causing them to go to "sleep". This is with better stabilized bullets than the previous scenarios. Comparable to a top when it settles down and becomes stable. In this case the wobbling of the boolit is mild enough that it "scrubs off."

NSP64

10-09-2010, 04:34 PM

Makes sense to me.

44man

10-09-2010, 05:43 PM

Long range needs MORE spin to start with and the bullet will rotate around the flight path until it slows enough to "go to sleep." A slow twist is more stable at close range but will lose stability at long range.
I always like a faster twist because you can reduce the load for close shooting but you can't load fast enough for long range with a slow twist.
Faster twists are easier to work with.
I only stray from this with muzzle loaders with a round ball.
Twist is so important for the distance you shoot, it is hard to explain.
A 1 in 22" twist for a .45 is WAY too slow and will never go to sleep. It never spins enough to start with.

fecmech

10-09-2010, 07:32 PM

Not in the same class as what you are talking about in the .25 but my .357 Rossi lever gun has a 1 in 30 twist. Shooting the Lee 158 rnfp at 1100 fps I can make 10 shot 50 yd groups of 1 to 1.5" with all bullets hitting point on,no ovals and they will not group inside of 3 feet at 100 yds! Any that manage to hit the target backer are going anything but point on. IMO this is a case of stability at 50 yds and no stability at 100.

Good Cheer

10-09-2010, 07:41 PM

Oh wow. Had one of those Rossi levers in '80. It was a tack driver at 100 with Lymans 358156 and just enough powder to coast it in. Total killing machine for head lighting jack rabbits across pastures. But I don't have a clue what the twist was.

GabbyM

10-09-2010, 08:00 PM

Right now this evening I think a bullet that is stable will settle down to go to sleep and stay that way. Bullets that are marginal will never go to sleep and in fact open up there spiral. I've never seen a 55gr SBT from a 12 twist 223 go to sleep.

One thing I do know is a M-193 ball round from a 1-12” twist barrel never goes to sleep. They do open up groups at long range and they do it suddenly before you get to a quarter mile. Depending, I've assumed, upon air temperature and pressure. Even on a warm day at five thousand feet they don't make it to a quarter mile before you all of a sudden can't stay on a three inch spotter or prairie dog. This goes for any of the 55 grain spitzer boat tails I've shot. Long or short barrels.

Can't explain the physics behind M-193 going nuts all of a sudden. Only parallel I have is my machine shop. When running tooling it either runs like a charm or when it decides to chatter they go nuts. Not much in between. Chatter marks on the work don't get larger they just stay the same horrible mess. Unless the tool point breaks off. That's mostly harmonic vibration.

trk

10-09-2010, 09:14 PM

mrbill2

10-10-2010, 10:37 AM

Ford SD

10-10-2010, 11:27 AM

I was at the range yesterday and shot this load out of my 308 with a1-12 twist. The bullet
was a Lyman 311334, 200 gr. cast from Lyman #2 and water cooled. The powder charge
was 20/A 5744, velocity I would guess around 1650 - 1700 fps. let's say. Light winds. I was
getting 5 shot groups from 1.250 to 1.5 at 100yds. I was happy happy. So I thought lets
shoot this puppy at 200 and see how things pan out. I realize 200 is not long range. Well to
say things went south would be a under statement. Groups were 6" or larger.
Two Questions. What made the groups become so large ? What can I do to get this bullet to
group better at 200 ?

not a expert but givein the number of people on this site you will get several excelent answers to your problem

your bullet has a bc of .340 length App 1.200
your vel at 200y is 1250-1300 +- and i think is border line stable (at 200 yds) only good bullet shape is keeping it from going in to the target side ways
i think you need a higher velocity even a extra 50- 100fps would help and may decrese group at 200

still good shooting for a first try at 200 yd seen a lot worse

GabbyM

10-10-2010, 12:37 PM

I think what Ford SD is saying is your bullet may have begun the dreaded transition to sub sonic flight.
Most bullets do a little dance as they transition to sub sonic. Maybe all bullets?

Doc Highwall

10-10-2010, 12:46 PM

mrbill2, good shooting. I am shooting something similar you can check out my post under reloading equipment titled Modifying Dies For Cast Bullet Shooting. Things get magnified when the shooting distance gets longer such as what was the wind doing at the firing line vs. at the target also what kind of rest are you using, do you have the parallax adjusted correctly if the scope even has it. They are even more like where you rest the rifle on the rest and do you place it the same shot to shot.

Shiloh

10-10-2010, 12:56 PM

I think what Ford SD is saying is your bullet may have begun the dreaded transition to sub sonic flight.
Most bullets do a little dance as they transition to sub sonic. Maybe all bullets?

I buy the subsonic transition that will cause a wobble. Then there are the grooves in the boolit to add to the complication. What about trying it with a paper patched boolit to eliminate some of the rifling variable??

SHiloh

Larry Gibson

10-10-2010, 02:56 PM

Eutectic is essentially correct except that his down range loss of rotation is exaggerated as over 530 yards the rotational speed decays very little. The rotational speed (RPM) does aversely affect the flight of the bullet as mentioned by the "spiraling" effect. The bullet is traveling point on BTW. At some point the velocity becomes low enough that the centrifugal force on the imbalances of the bullet cause complete loss of stability. That loss of stability can happen in a short distance or it can happen at very long range depending on the bullets suitability for the RPM.

Let's take a look at Palma shooters for an excellent example. The Palma match is shot at 800, 900 and 1000 yards in strings of 15 shots at each range. Originally when the Palma matches were restarted in the 50's the requirement was for the host nation to provide their service rifles and 7.62 NATO spec ammunition with a 145 - 155 gr fmj service fmj bullet. After a match or two the rules changed because the "home Team" always had the advantage of using their own rifles. The 1st change was to allow the teams to bring their own service rifles in 7.62 NATO and the Host nation still provided the ammo. That didn't work out well enough so they allowed "match rifles" to be used. It was quickly found that the service grade ammo didn't shoot well in 10" and 11" twists. It shot better at the longer ranges in 12" twist. It also shot better with longer barreled 12" twist.

It was during this period of matches and practices that it was realized that the increased velocity from the longer barrels was keeping the bullets (145-155 gr service FMJBTs do not have a really high BC) transonic to 1000 yards. It was also realized the RPM of the twists was causing a large accuracy reducing spiral at lng range with the imbalanced service grade NATO spec bullets (we all know milsurp bullets are not as well made, read that as “balanced”, as commercial bullets and are not as accurate because of this). Thus the slow twist barrels developed. It became standard to use 13 or 14” twist 27.5 – 32” barrels for Palma matches. This was to shoot the issue 7.62 NATO spec ammunition with the most accuracy.

The rules of Palma Matches again were changed to allow the teams to supply their own ammunition and reloaded ammunition was allowed with match grade bullets. Then the rules were again changed to allow any cartridge/caliber as long as the bullet weighed in at the NATO spec of 145 – 155 gr. Thus we see the 6.5 caliber pretty much rules the matches today. Many of us lament the rule changes to suit the high power shooters. The rules should have at least stuck with service type rifles and the current or past NATO cartridges. Today it has lost its “romance” and is now just another long range belly match with single shot rifles.

It all developed that way because slowing down the RPM and using a longer barrel to increase velocity was the way to get the best accuracy with the imbalanced bullets and velocity of the issue service grade ammunition. The same principles apply to cast bullets but they apply earlier because of the greater imbalances in cast bullets. However, the more balanced we can cast the bullet, load it and keep it balanced through acceleration the more accurate it will be. I have promoted the RPM threshold concept here for some time but that concept did not originated with me. It originated with numerous cast bullets shooters and their writing many years ago as the lessons from the Palma rifle development was applied to cast bullets. The 1st time I read about was when a fellow asked;

Why is it I can load a 311359 to 40,000 psi in a .30 carbine and get excellent accuracy and yet when I load the same bullet to the same psi in a ’06 the accuracy is non existent?

He proceeded to answer the question by explaining that the real difference in accuracy was not based on psi but simply that the .30 carbine had a 18” twist and the ’06 had a 10” twist. It was the increased RPM of the ’06 load that caused the inaccuracy. I have conducted many experiments with varied twists and have found that to be the case. Most all of you have also found that to be the case but many do not realize it yet.

But the point here is that with cast bullets in particular we must control the RPM for best accuracy with a specific bullet. That is done, other things being equal, by adjusting the velocity. If we want to get into the realm of accuracy at high velocity then we must understand the adverse affect that RPM has on the imbalances of cast bullets, particularly above a certain level of RPM. The easiest way to consistent accuracy at high velocity with cast bullets is to use as slow a twist as will initially stabilize the chosen bullet at the expected velocity. The yaw and pitch will smooth out and the bullet will “go to sleep” at longer range with better accuracy because the RPM increases relative to the bullets loss of velocity at longer ranges as Eutectic mentions.

In the case of the 250 with the 10” twist the long RCBS 120 gr cast bullet as it was cast and loaded was being pushed to too high a velocity/RPM and inaccuracy resulted.

Larry Gibson

sagacious

10-10-2010, 03:03 PM

My first question: "Why is stability less at 300 yards than at 100 yards?"
I am slightly hesitant to join in, but let's see how it goes. You may wish to define your interpretation of 'stability' to move forward with that question. There are several different ways in which a bullet can be 'stable.' I suspect that you mean gyroscopic stability along the course of the trajectory.

A bullet may be more stable, or less stable, at longer ranges dependent on a host of variables.

I would not forget his comment 'go to sleep'....... But what is it????
Hard to know what was meant exactly, as it relates to what was happening physically, but probably a diminishment of yaw relative to trajectory.

If we calculate 2000fps in a 14" twist I get 102,857 RPM at the muzzle....

If we calculate 1000fps in a 14" twist I get 51,429 RPM...

Is this the correct RPM at 530 yards for our example load above then?

The boolit in our example load above leaves the muzzle of our rifle 'locked in' at departure turning one 360 degree revolution in 14" of travel.
No, the second rpm figure is not correct for 530yds. The rpm at muzzle is not "locked in", it's simply the rate with which it begins. Calculating rpm based on at-distance velocity is not accurate. Rpm and forward velocity are two properties that do not diminish in sync, as easch is subject to distinctly different forces.

Note that there seems to be a slight confusion of terms: Rate-of-twist (rot), rate-of-spin (ros), and rpm are not synonymous. Unlike rpm, rot does indeed start as an invariant factor. Rpm will vary as a function of initial velocity and decrease with time-of-flight, and ros will decrease as angular momentum decreases. Rot does not change, because rot is simply the rifling pitch rate, and that can't change unless the gun is rebarrelled. Rot = ros at muzzle, but not at distance. This fact is at the very heart of your question.

OK... A tougher question.... At 530 yards does our bullet still travel 14" to make one full (360 degree) revolution?
No, it travels slightly further than 14" to complete a full revolution, because the ros at distance has slowed from the rot at muzzle.

Let's say we lose 20% of our RPM over 530 yards or more easily looked at we have 80% of our original RPM that we had at the muzzle. That figure is 82,286 RPM. I think it could be higher... we are only talking 1.175 second of flight time here.

So if you allow me the 82,286 RPM figure and we calculate this against our 530 yard retaining velocity of 1000fps to get a theoretical 'twist' for these numbers the twist would then be the equivalent of 1 turn in 8 7/8" for our boolit!!!!!
If the rpm slowed by 20%, then the bullet would have to travel 20% further to complete a revolution, not 20% shorter. Also, taking for granted your rpm figure, still, the ros calculation at 530yds is not correct. Your math shows the bullet revolving faster than 1:14" at distance. Where did it's ros get the energy to increase from it's initial rot? Of course, the ros cannot speed up unless energy is being added. Rot is always >or= ros.

Just hoping to clarify, and respond to the questions given. Hope this discussion stays friendly. Good luck, and thanks for posting your thoughts. Good stuff!

Regards, and good shooting! :drinks:

44man

10-10-2010, 03:56 PM

Much good stuff here. It always comes down to the bullet or boolit, the length and weight when looking for the proper twist.
Been a long time from my long range varmint days but the .220 Swift was always better with heavier bullets then the .22-250 because of the faster twist. That made the Swift much better at long ranges to well beyond 600 yards. But the Swift sucked at close range because of over spin so I did not bother to sight in anywhere except 350 yards.
That means you need to also look at the distance you want to shoot.
Now that most of my work is with revolvers, I found the faster twist rates of BFR revolvers has made it so easy to find accuracy to 500 meters while making tiny groups at 50 yards. My love of the longer barrels also figures into it because velocity achieved is important for stability. I argue time and time again that a 4" barrel with the same TR as a 7-1/2" is not as stable because you can't match the velocity unless you use fast powders that ruin boolits. The spin from a short barrel is less then from a longer barrel UNLESS you match velocity. I feel that the shorter the barrel, the faster the twist needs to be so it matches the velocity.
I see it with a friends Marlin .44 that has the same twist of 1 in 38" as mine. My barrel is short. He gets better accuracy with his longer barrel then I can with my short barrel so I need more powder and pressure.
Going to sleep is when an over spun bullet loses both spin and velocity so it settles into smoother flight. A boolit spun too slow will not go to sleep but will get unstable at long range from lack of spin and the transition from supersonic to subsonic will affect it much more. Spun correctly and the transition has almost no affect. Keep the boolit or ball subsonic from the muzzle out and stability can still be good and so can keeping the bullet supersonic to the target.
Ask me what twist your rifle needs and you will get a blank expression because I don't know the bullet, the velocity or the distance.

Eutectic

10-11-2010, 11:01 AM

Eutectic --

What you write is consistant with Dr. Franklin Mann's writings (1920's) in The Bullet's Flight.

Well worth the reading. (If you don't want to buy it, get your library to get it for you - ineter library loan.)

trk,

Thanks for the info. I believe my good friend has this Mann book. I will borrow it while this discussion is fresh!

Eutectic

mrbill2

10-11-2010, 11:03 AM

" mrbill2, good shooting. I am shooting something similar you can check out my post under reloading equipment titled Modifying Dies For Cast Bullet Shooting. Things get magnified when the shooting distance gets longer such as what was the wind doing at the firing line vs. at the target also what kind of rest are you using, do you have the parallax adjusted correctly if the scope even has it. They are even more like where you rest the rifle on the rest and do you place it the same shot to shot. "

I'm using a Caldwell rifle rest with a position stop and a Weaver T36 with parallax adjusted. I think I'm doing everything right as far as shooting the gun I just need to follow the instructions from Ford SD and Gabby M and speed the bullet up. I'll give that a try next time I get some loaded.

There is one thing that I could never understand with this RPM stuff. Why the math formular includes x 60 to convert the answer to RPM's. It would seem the me that RPS (per second) would be more appropriate as no bullet has a flight time anywhere near 1 minute. But I'll leave that stuff up to the experts.

Thanks to all for the advice.

82nd airborne

10-11-2010, 11:04 AM

Spin drift is also a factor at extended ranges, im guessing to to the same thing?

Eutectic

10-11-2010, 12:24 PM

Hi Sagacious,

I have taken the liberty to pull a few of your comments from your post. I have responded with my thoughts to them in blue. Please respond with your thoughts especially where I am wrong.

"I suspect that you mean gyroscopic stability along the course of the trajectory."

Yes... Stability along the centerline of the projectile axis.

"No, the second rpm figure is not correct for 530yds."

Yes! That's the point I was after! IT IS NOT THE CORRECT RPM AT 530YDS.

"Calculating rpm based on at-distance velocity is not accurate."

True.

"The rpm at muzzle is not "locked in", it's simply the rate with which it begins."

By 'locked in' I mean the values induced by gas pressure and rifling twist are over at the moment our projectile leaves the lands and grooves... The values of forward speed and rotational speed are 'locked in' and measureable... This does not mean they are 'locked in' after our disconnect! If fact, rotation and forward travel are not 'locked in' the same again. In the atmosphere each dynamic (rotational and forward travel) has its own set of variables and this is where confusion sets in.

"Rpm and forward velocity are two properties that do not diminish in sync, as easch is subject to distinctly different forces."

This sentence seems to contradict itself... Maybe 'diminish' is confusing me. Could you please explain again?

"Note that there seems to be a slight confusion of terms: Rate-of-twist (rot), rate-of-spin (ros), and rpm are not synonymous. Unlike rpm, rot does indeed start as an invariant factor. Rpm will decrease as forward velocity slows, and ros will decrease as it's angular momentum slows. Rot does not change, because rot is simply the rifling pitch rate, and that can't change unless the gun is rebarrelled. Rot = ros at muzzle, but not at distance. This fact is at the very heart of your question."

Your (rot) is my 'locked in' and is only relevent while our boolit is still engaged in the rifling.. Your (ros) muddies the waters with confusion and is probably not needed.... Downrange Boolit RPM (rotation over time) coorelated with Boolit SPEED (distance over time) will allow computation of our HELIX LENGTH where ONE full 360 degree rotation of our boolit has taken place. THIS IS the very heart of the question...

Quote= (OK... A tougher question.... At 530 yards does our bullet still travel 14" to make one full (360 degree) revolution?)
"No, it travels slightly further than 14" to complete a full revolution, because the ros at distance has slowed from the rot at muzzle."

I disagree with you here. Please explain how the 14" HELIX (again I use the term 'HELIX' in our case for the length of ONE full 360 degree rotation of our boolit) holds constant over 530 yards as two different sets of variables are at play, one for rotation and one for forward speed?

Quote=(Let's say we lose 20% of our RPM over 530 yards or more easily looked at we have 80% of our original RPM that we had at the muzzle. That figure is 82,286 RPM. I think it could be higher... we are only talking 1.175 second of flight time here.
So if you allow me the 82,286 RPM figure and we calculate this against our 530 yard retaining velocity of 1000fps to get a theoretical 'twist' for these numbers the twist would then be the equivalent of 1 turn in 8 7/8" for our boolit!!!!!

"If the rpm slowed by 20%, then the bullet would have to travel 20% further to complete a revolution, not 20% shorter."

I don't think so. What is missing here?

"Also, taking for granted your rpm figure, still, the ros calculation at 530yds is not correct. Your math shows the bullet revolving faster than 1:14" at distance. Where did it's ros get the energy to increase from it's initial rot? Of course, the ros cannot speed up unless energy is being added. Rot is always >or= ros."

I believe we are looking at less rotational energy lost, not energy added for the RPM figure. I think we agree at the bullet's departure from the rifling that for our example the RPM is 102,857. I used a loss of 20% of rotational speed over 530 yards. I believe the loss is even less.... so does Larry Gibson.... Regardless of our opinions, 80% of the RPM at muzzle is the 82,286 RPM figure. We cannot forget velocity (our forward speed) at 530 yards is now only 1000fps.... This could have happened?

I see this happening at 530 yards for our example.....

82,286 RPM divided by 60 = 1371.43 revolutions per second. (RPS)

1 divided by1371.43 RPS = .00073 second (the elapsed time for one revolution)

1000 feet per second remaining velocity X 12 = 12,000 inches per second.

12,000 inches X .00073 second = 8.76" travel for one bullet revolution or the length of our 'HELIX' as I am using the word in our discussion.

Again, please explain how your 'ros' remains a constant while our other dynamics are changing continually along our boolit's flight.....

"Just hoping to clarify, and respond to the questions given. Hope this discussion stays friendly."

I do as well... I look forward to your thoughts!

Eutectic

felix

10-11-2010, 01:54 PM

We should never assume the boolit is actually doing the twist upon muzzle exit according to the calculated spec. Here we enter the 44man's arena of his saying the faster twists in his revolters are proving to be "mo'betta". ... felix

Eutectic

10-11-2010, 03:40 PM

felix,

I understand your point of some slip and slide in the high pressure .44 loads especially in short length barrels.... But don't you think our mild rifle load example in a 24" barrel with a fairly slow twist would be fairly close?

Eutectic

sagacious

10-12-2010, 03:09 AM

Hi Sagacious,
Yes... Stability along the centerline of the projectile axis.
That is probably not what you mean. The bullet can be stable along it's axis, but unless the gyroscopic axis roughly follows the trajectory, the bullet will not be stable in flight. The bullet can spin just fine along it's own axis, but unless the two axes coincide for the nduration of flight, the bullet may become dynamically unstable. Stability along the bullet axis does not equal stability in flight over time.

"Rpm and forward velocity are two properties that do not diminish in sync, as each is subject to distinctly different forces."

This sentence seems to contradict itself... Maybe 'diminish' is confusing me. Could you please explain again?
Diminish = decrease. Rpm and fv do not decrease in synchrony; thus calculation of rpm cannot be determined by velocity at distance. For rpm to be calculated precisely, one has to take into account the loss of spin over time. Standard calculations of rpm give only the accurate rpm at muzzle.

Downrange Boolit RPM (rotation over time) coorelated with Boolit SPEED (distance over time) will allow computation of our HELIX LENGTH.
This is in error, because the ros at 1:14 lengthens over time, and is totally independent of downrange velocity. For example, a bullet fired perfectly vertically will reach 0fps at the apogee of it's trajectory, but will still be spinning very fast. Ros and velocity are in no way coupled.

I disagree with you here. Please explain how the 14" HELIX (again I use the term 'HELIX' in our case for the length of ONE full 360 degree rotation of our boolit) holds constant over 530 yards as two different sets of variables are at play, one for rotation and one for forward speed?
The term 'helix' is not used correctly for this discussion. The bullet in flight usually describes a helix with it's point or cg relative to the trajectory. Ros is what you're describing, as the helix and ros or rpm are unrelated. It may be better to use a term other than helix.

Rotation is also correct, but revolution is not correct for this discussion. For example, the Earth rotates about it's axis, but it revolves around the Sun. The Earth does not revolve about it's axis, nor does a bullet. Rotation and revolution are not synonymous. Just a point to help clarify.

The 1:14 ros does not hold constant; it must lengthen over time as the angular momentum of the bullet decreases. Put another way, the distance over which the bullet makes one full rotation increases over time as drag slows it's rate of spin.

Ros may be the best term, as we're describing the rate at which the bullet spins (such as 1:14")-- same as we use twist rate (rot) for the rate at which the rifling turns (such as 1:14").

1000 feet per second remaining velocity X 12 = 12,000 inches per second.

12,000 inches X .00073 second = 8.76" travel for one bullet revolution or the length of our 'HELIX' as I am using the word in our discussion.

Again, please explain how your 'ros' remains a constant while our other dynamics are changing continually along our boolit's flight.....
As I noted above, ros cannot remain constant. It lengthens over time.

I checked your math very carefully. The problem is that you're still using downrange velocity to calulate the rate at which the bullet spins (1:8.76"). This will not work, as the rate of spin and rate of fv decrease happen at different rates, so one cannot use the downrange velocity to calculate the distance the bullet travels to spin once (ros).

I suspect there may a measure of miscommunication by either one or both of us. If I'm misunderstanding your questions, just let me know.

A pleasure discussing with you, regards and good shooting! :drinks:

rvpilot76

10-12-2010, 05:49 AM

Here's a thought:

If you have an unbalance tire and travel at say, 45 MPH, you feel the shake in your steering wheel. Now take that same unbalanced tire and travel at 70 MPH. In my experience it's not as noticeable. Think of the shake in terms of frequency. At high speeds, the frequency is so high that it is almost imperceptible. At low speeds, however, it is. I may be off here, but think of the frequency cycle as a direct correlation to group size. The slower the round, the lower the frequency, the greater the spread of the frequency between the peaks and valleys of the frequency, the greater the group size. This explains, in some way, the loss of accuracy (or increase of frequency "spread") at longer ranges. Not a fix all, but I hope I have increased your understanding of the subject matter involved.

Kevin

44man

10-12-2010, 09:27 AM

When we shot IHMSA, we watched many boolits and bullets in flight. We seen some mighty strange things.
I do not know the twist rate of the S&W 29 but the 240 gr bullets would rotate around the flight path like a corkscrew with the powder charge that was the most accurate. It seemed to settle some at long range but it gets very hard to track the bullet with a spotting scope.
This did not affect accuracy and I shot many, many 1/2" groups at 50 meters but it would change POI at other ranges, not enough to worry about.
By going to a 250 gr bullet or boolit, this rotation was gone. The Rugers did not have this rotation at all and boolits flew a straight path if you discount drop.
The BFR's have not been watched but since heavy boolits are used, when sighted at 50, they stay on line to as far as I have shot them which is 500 meters, a lot of drop but accuracy is still there. I do know the guns do not like real light boolits for the calibers while the Freedoms and Rugers prefer a lighter boolit because of the slower twists or more powder is needed for a boolit weight increase. Not drastic, maybe 1/2 gr more powder then the BFR.
Then there was the TC 30-30 with a cast boolit. It was accurate but when watching the boolit go downrange, it would go sideways like it was going to hit the next ram over, come back on line and hit the one aimed at. It caused a lot of laughter and we took turns watching it. The boolit was not wobbling or rotating, it just veered off. At other distances, it hit a different POI on each target, only windage.
Now my .220 Swift with 60 gr bullets. (Pre 64 model 70.) I never shot a group at 100 under 1", mostly larger. I sighted at 350 yards only and head shot chucks beyond 600 yards.
One day while sighting I shot a five shot 1/4" group at 350 yards. A fluke---maybe! But I learned the bullet did not "go to sleep" until out there. The over spun bullet was an advantage at long range.

44man

10-12-2010, 09:55 AM

Now I have to look at my Browning BPCR with a 1 in 18" twist. I have every weight boolit you can think of and have shot some 200 meter groups of 1" from the bench but I can not hit the 500 meter rams. In years I have not discovered the right boolit length or velocity because velocity is limited with BP. Sometimes I did good but any change at all would be a total loss.
It has to be the hardest sport ever and it seems only certain guns work and the same guys win all the time. Do they have a faster twist? They will not say.
My BFR 45-70 with a 1 in 14" twist will out shoot the rifle to 500 meters BY FAR. If it was possible to adjust the sights for each range and I was allowed to use it, I bet I could shoot a 40. To hit steel I have to aim at a tree limb about 26' over the ram. Each ram does not have THAT tree limb! :holysheep
I hate math, I hate Greenhill, I hate predictions! I go by what I see and shoot only.
Now the military has a rifle with a computer that figures in everything before pulling the trigger so a one shot kill can be made at extreme ranges. Makes a guy feel real stupid. [smilie=l:

felix

10-12-2010, 10:24 AM

44man

10-12-2010, 10:49 AM

Eutectic, I hear ya' loud and clear, and your reasoning seems right on. The fly in the ointment comes when we take the many DIFFERENT batches of boolits and they can be seperated ONLY by the target results. This means each boolit within a group was as identical as is possible by home means. Weight, hardness, sizing, lube, casting condition, and you can name the remaining. The only thing left was the rotational results of each boolit BEFORE and AFTER being shot.

I never get tired of thinking about the Iowa class of guns. I remember the Navy(?) asking for sign-up interviews at MU of its graduating seniors, 1963 in math/engineering. The job was working on "Fire Control" applications. At that time I was surely not interested in putting out fires on Navy ships, so what a mistake on my part for not at least asking the question of someone in the know about just what are they talking about. Now, of course, I know that would have been one interesting job for me. Just think, a moving bench with a moving target up to 26 miles away, and hitting that football sized target on every shot (a turrent's worth?). ... felix
Amazing what the military has done. How great to know all of it. But at today's dollar value, we are talking BILLIONS of tax payer dollars when we complain about over $20 for a can of powder.
Wouldn't you love to run full speed through the woods and hit a deer also running full speed?
No, I don't think so, it is not hunting or personal ability. Might just as well hunt with a grenade. There is just something right about shooting a revolver off hand and dumping a deer to 100 yards instead of putting the gun in a turret with computer aiming.

felix

10-12-2010, 11:14 AM

All sports have their intentional limitations, and deer hunting is no less a sport. I kinda' wonder about using scopes, but then we are branching into varmint hunting. Start using benches, we are talking about targeting groups. I have quit group shooting in the last few years, and just use KY windage, scope or no scope. I get the scope into range by shooting once and moving the crosshairs to match the target. ... felix

Eutectic

10-12-2010, 12:46 PM

I hate math, I hate Greenhill, I hate predictions! I go by what I see and shoot only.

I love it 44man! ... You have convinced me to drive over to Billings and borrow a gun from an old friend. I don't have a .250 Savage in 14" twist but he does....

I need to answer a few questions for myself... Let's see what gun, caliber, load, boolit, velocity, twist, and 530 yards have to add to this hypothetical example we have kicked around like a football from the keyboard in this thread!

By the way..... What is the rifling 'twist' rate in the 16" guns used in the "IOWA" class of battleships?

Eutectic

felix

10-12-2010, 01:26 PM

Don't know about the twist, but it is guaranteed to be microgroove. The lands/grooves are a triangle in shape. Looks like an inch deep or better, when looking up at a fairly straight barrel overhead. ... felix

44man

10-12-2010, 01:33 PM

Now look at the tank rounds. Sabot's and smooth bore barrels. Hit another tank while going balls to the wall over rough country.
We need fin stabilized boolits. [smilie=s:

felix

10-12-2010, 01:49 PM

44man

10-12-2010, 02:18 PM

It would be very interesting for me to see what parameters, both input and output, the computers are using from and including targeting through firing. I know how the programs work, but not the data. I must assume GPS is involved big time nowadays. ... felix
Not me. I repaired TV's and radios part time for many years. I majored in auto mechanics in school. I worked for an airline for 42 years.
But today I feel like I crawled out of a cave and discovered ---ROCK! :mrgreen:

Larry Gibson

10-12-2010, 02:28 PM

sagacious

........ The bullet can be stable along it's axis, but unless the gyroscopic axis roughly follows the trajectory, the bullet will not be stable in flight. The bullet can spin just fine along it's own axis, but unless the two axes coincide for the nduration of flight, the bullet may become dynamically unstable. Stability along the bullet axis does not equal stability in flight over time.

Just a bit of further clarification regards to inaccuracy;

The bullet doesn't necessarily become dynamically unstable . If the gyrascopic axis is aligned with but not coaxial with the trajectory the bullet travels in a spiral around the axis of trajectory. The greater the imbalances of the bullet and the greater the centrafugal force (higher RPM) the greater the spiral around the axis of trakectory. This is fundementally why bullets shoot groups and do not shoot into one hole.

Many erroniously think that "stability" means the bullet is pointing forward and any inaccuracy caused by "instability" means the bullet is unstable and tumbling. Such is not the case. The rest of your post is very well put and correct. I:drinks:

Larry Gibson

sagacious

10-12-2010, 07:44 PM

The bullet doesn't necessarily become dynamically unstable . If the gyrascopic axis is aligned with but not coaxial with the trajectory the bullet travels in a spiral around the axis of trajectory.

Larry Gibson
Larry,
You are of course right on. I thougth about that aspect when I replied, but decided not to add precession to the mix. In fact, and as you know, because of the magnus force, the bullet never flies perfectly point forward, but always slightly off. We're probably not at that point in the discussion yet. :)

Best regards to you and yours. :drinks:

c3d4b2

10-12-2010, 08:09 PM

Thanks to Google you are able to read Dr. Franklin Mann's "The Bullet's Flight"on your computer

http://books.google.com/books?id=QdQqAAAAYAAJ&lr=&pg=PP1#v=onepage&q=&f=false

NSP64

10-12-2010, 08:26 PM

My head hurts:groner:

I used to shoot RB out of my ML 1-24 twist. I just adjusted powder down untill it started shooting tighter groups.

NSP64

10-12-2010, 08:46 PM

So, in a nut shell if it has a slower twist, you will have to shoot it faster for any given weight of boolit, than a faster twist barrel to get it to stabilize.

For instance.
Bullet A out of 1-14 barrel 1900fps
Bullet A out of 1-10 barrel 1700fps

rvpilot76

10-12-2010, 09:26 PM

In a nutshell, yes.

Eutectic

10-12-2010, 09:52 PM

Thanks to Google you are able to read Dr. Franklin Mann's "The Bullet's Flight"on your computer

http://books.google.com/books?id=QdQqAAAAYAAJ&lr=&pg=PP1#v=onepage&q=&f=false

Excellent!! .... Thanks for posting!

Eutectic

Dannix

10-12-2010, 11:05 PM

I have not had a chance to read this whole thread, but here's the little bit that I've read about balanced flight. It's not exactly coming from an unbiased source, but perhaps it's spot on?

Balanced Flight
It is clear that a projectile being able to retain stability throughout its flight will go farther and will be more accurate. Warren Jensen, partner and designer at Lost River Ballistic Technologies® identified the conditions that could be translated into projectile design, which would exhibit very long distance accuracy. The concept is called Balance Flight and is patented (6,629,669).

Working with PRODAS software, Jensen designed projectiles in multiple calibers, where the linear drag on a projectile is matched to its rotational drag. In other words, forward rate of deceleration and an axial rate of deceleration are balanced. The gyroscopic stability remains constant resulting in the projectile remaining on its original trajectory path. Non-balance flight occurs when a projectile’s spin is too great, thus leading to an "over spin" of the projectile. Over spin leads to increasing angles of repose, which result in increased drag and can result in instability at the transonic threshold.

An important component of Balanced Flight is the design of the barrel lands and grooves. A ratio of a total surface of the projectile to a total surface area of the physical feature must be in the range of 3.00:1 to 4.00:1. As a result of projectile and barrel land / groove design, the drag coefficient is reduced to a range of 0.100 to 0.250. In addition, the bearing surface of the projectile has a depth equal to 1% of the caliber of the projectile and a ratio of a total surface area of projectile to the total surface of the physical feature in the range of to 3.00:1 to 4.00:1. The purpose is to impart an ideal axial surface friction upon launching, which during flight produces a trajectory characterized by a continuously decreasing rate of axial deceleration.

Balanced Flight is best associated with the .408 CheyTac® caliber. However, Jensen first designed projectiles in 30 caliber, which resulted in major
improvements over existing projectiles in this caliber.

Balanced Flight’s improvements of projectiles in the 40 caliber went far beyond expectations. Could a Balanced Flight improve the 50 caliber projectiles? The answer is yes, but it would require specific changes to standard 50 BMG land, groove, and twist configurations. Combined with the CheyTac® cartridge case, the .408 projectile has found an ideal launching platform. This platform represents the best long-distance cartridge to date – in all ballistic-characteristic, including kinetic energy.
http://www.cheytac.com/WhitePapers/Cheytac%20white%20paper%20V2.pdf

Bullshop

10-12-2010, 11:32 PM

Dannix
That is very interesting stuff. I recently built a 22 cal rifle with a 6.5" twist. It was built for 90gn vld bullets. One big difference with this Walther barrel is that it has no lands or grooves, it has a polygonal interior with the 6.5" twist. I wanted to try this type barrel to see if it would foul less than conventional rifling. Now after reading this I wounder what effect if any it may have on drag.

44man

10-13-2010, 09:54 AM

Still makes my head hurt! :bigsmyl2:
Maybe we should shoot round balls! I grew up with round ball muzzle loaders and built many of them. I always read they go to pot after so far and it is the reason for the fast twist inline rifles, so you can shoot farther. Actual advantage to the bullet shooting guns is trajectory, it is flatter.
Take my .54 Hawken. I use 100 gr of powder for normal shooting to 100 yards and it is extremely accurate. It is still accurate at 200 meters but to get a flatter trajectory I go to 120 gr. Add sight adjustment and I hit 4 out of 5 chickens off hand at 200 meters and the gong is just too easy.
The twist is 1 in 60". I do not know just how far the ball will maintain accuracy but I suspect until it hits the ground.
Now take a 1 in 48" twist and a round ball. Reducing the charge a little and it still shoots great but a Maxi ball will also shoot great with the same charge so we are getting into boolit stability too. The 1 in 60" twist will spray boolits.
The super fast twists of inlines means bullets only but if you just pop out a round ball, I suppose it will be decent.
So the over spin on a round ball does not work and the bullet under spun does not work either.
To be practical, we work loads for each projectile to find the velocity where it is accurate. That relates to spin and stability but also relates to the range to be shot.
Too much spin is as bad as not enough. Barrel length does enter into it because of the velocity you can achieve so I feel the shorter the barrel, the faster the twist should be. Could this be why the BFR revolvers work so well? I would love to try a 1 in 16" twist with my 45-70 BPCR too because velocity is limited.
We see all the math and design of special bullets but just how does it relate to cast boolits?

Larry Gibson

10-13-2010, 12:08 PM

The super fast twists of inlines means bullets only but if you just pop out a round ball, I suppose it will be decent.
So the over spin on a round ball does not work and the bullet under spun does not work either.

Not quite the case. To use 44mqan's example of the RB in a ML I shoot RBs in a TC Black Mountain Magnum .50 cal. It is a side lock not an inline but it is made for 150 gr Pyrodex charges and saboted bullets so it has the 28" twist. I worked up a very decent RB load at 1950 fps using FFFG Triple 7. They would shoot into 1 - 1.5" at 50 yards (shot several 5 shot groups. I then moved the target to 100 yards to get a zero and the groups were 16"+! I thought I'd done something wrong so I repeated the 50 yard test; same thing, 1 - 1.5" group. Moved the target back to 100 yards and the same thing; a 16+" group. I slowed the RBs down and did the testing at 100 yards. At arond 1650 fps I was getting 2.5 - 3" at 100 yards. Moved the target to 50 yards and shot a 1.5" group. MaxiBalls (cast of 1-16 alloy) shoot into 2 - 3 moa at 100 yards at 1570 fps.

The same thing can be observed with other bullets, especially cast bullets. If the bullet is severely imbalance the group dispersion will not be limear as range increases. As an example a test I conducted for Bass was comparing M118 bullets with unbalanced (purposely) M118 bullets. Ten shot groups were fired with at 50, 100 and 200 yards. The rifle has a 10" twist and velocity was 2666 fps. The balanced bullets shot into groups with linear expansion of group size. The unbalanced groups showed a definate decrease in accuracy and non - linear expansion of groups as the range increased.

This also applies to cast bullets when we drive them above the RPM threshold. The same test was also done with 311291 at 1912 fps and at 2487 fps. The slower 1912 fps load was below the RPM threshold and gave 10 shot groups of .7" at 50 yards, 1.55" at 100 yards and 2.5" at 200 yards. This obviously shows a linear expansion of the groups and good stability. The 2487 fps gave 10 shot groups of 2.55 at 50 yards, 4.7" at 100 yards and 14.5" at 200 yards. Obviously the linear expansion was greater with the faster and more unstable load that was over the RPM threshold.

This test is easily reproduceable and predictable. It is also the reason not to test at 50 yards with rifles if pushing over the RPM threshold. It is also a good reason to test at the maximum range to be shot when confirming what appear to be "accurate" shorter range tested loads.

Bottem line; a RB can be over stabilized as can be any other bullet; jacketed or cast.

Larry Gibson

44man

10-13-2010, 01:42 PM

Larry, you said the same thing I did. Slow the round ball in a fast twist and it does OK. However, I like better accuracy from the ball.
This is what I want at 50 yards for 5 shots and no more then double that at 100.
By the way, that is with open sights.

44man

10-13-2010, 01:51 PM

Reading Larry's post again shows we are in total agreement for much of the discussion so I don't understand the "not quite the case" wording????

Bullshop

10-13-2010, 02:01 PM

Larry
A bullet or boolit understabalised will do the same thing. I had an experiance with a 38/55 with 1/14" twist shooting 330gn boolits with a muzzle velocity of 1400 fps.
I wont bother going out to measure them for length but suffice to say that with the 1/14" twist at 1400 fps they were marginally stable.
I was preparing for a long range gong match and felt I had developed a really good load. It was grouping very well at 100, 200, and 300 yards. I dont have actual group sizes at each range but it was about proportional to the range increase.
Then surprise!!! past 300 yards they began to have an audible buzz in flight. At 500 yards I was doing good to keep them in the same hay field with my target, SHOCK!
The fix was a slightly shorter boolit. With the shorter boolit at about 300gn everything stayed together nicely and the gun/load did well at the shoot to the longest range we shot, 800 yards. The lesson for me was just because a load does good at moderste range do not assume it will continue to do good at longer range. Shoot to be sure.
In what I have read from the old masters of the 1890's and early 1900;s they seemed to prefer the absolute minimum spin for the range they were shooting, and steared clear away from more than enough spin.

7br

10-13-2010, 02:54 PM

I hear comments on this forum all the time about slower rifling twists for cast bullets... Let's call them 'Borderline Twists'... It is an old philosophy with cast bullets, and many 'old masters', even Harry Pope, believed this way.

My first question: "Why is stability less at 300 yards than at 100 yards?"

If we calculate 2000fps in a 14" twist I get 102,857 RPM at the muzzle....

If we calculate 1000fps in a 14" twist I get 51,429 RPM...

Is this the correct RPM at 530 yards for our example load above then?

OK... A tougher question.... At 530 yards does our bullet still travel 14" to make one full (360 degree) revolution?

Eutectic

Disclaimer: I am not an expert.

First question(SWAG answer) : Think about a top. You start spinning and it and it wanders around a center point for awhile, settles down and stays on its axis, then goes to unstable. I think this is called precession and you might google it and come up with some good information.

Second Question: The rpms at 530 yards will be mostly independant of the velocity. Once the bullet exists the muzzle, the only angular forces acting on it will be drag from the air. My guess that the higher the rpms, the faster you will lose rpms.

Third question:
Really tough. If the rpms have slowed down to exactly 1/2 what they were at the muzzle, then the answer is yes.

Lets see if I can cypher this out.
Time for 1 revolution will be 1/ ((rev/min) *1min /60s)
Distance for 1 rev will be velocity f/s *12in/1ft * time for 1 revolution
So Velocity in f/s * 12 in/ft *1/ ( rpm in rev/min * 1 min/60s)
Simplify (V in ft/s * 12 in/ft ) * 60s /rpm in rev/min
V at distance*720 /rpm at distance will give you how many inches it takes to complete one revolution. The rub is trying to measure the rpm at that distance.

Some one check my math

Hey Forearmed, this is classic physics stuff. Care to comment?

44man

10-13-2010, 04:16 PM

Oh I hate math! :kidding:
But the question is--what should the spin be at 500 or 1000 yards for stability, compared to the velocity? What is the starting spin for each velocity? What is best for 100 or 200? What if boolit length is changed?
I have to side with Bullshop and might need a shorter boolit in my Browning. So many BPCR shooters tout long, heavy boolits but that might be wrong for the twist rates.

Larry Gibson

10-13-2010, 05:57 PM

44man

Boy did I ever misread what you said:-( Definately my bad and please accept my appology. We both indeed said the same thing.

Bullshop definatel that is also the case. We see many examples of that at shorter range with handgun loads that shoot well at 50 yards but poorly at 100 yards. Same with low end .22 Hornet loads with a 16" twist. Mine will shoot 225415s like a house on fire at 50 yards but it groups improved cylinder at 100 yards if velocities are under 1800 fps.

It is very noticeable with pellets in pellet rifles as we extend the range. At some point the pellet just loses it and goes helter skelter.

Larry Gibson

herbert buckland

10-13-2010, 06:44 PM

I have had the problem of trying to get a replica spencer 56-50 to hit any thing at100yds, the the twist rate is 1 in 20 (way to fast for a .521cal .775 long bullet,that is needed to cycle properly in the Spencer)I can get very good 100yd acuracy with a .975 long bullet but because the OAL can not exceed 1.61 to work the pouder charge has to be reduced to 28gr FF black,what I am after is a twist rate that will be acurate from 50 to 300yds with a velicity of around 1000fps yousing the shorter bullet.can any one work out what would be the best twist rate for this that would be stable over this distance given the volicity and bullet lenth problems

NSP64

10-13-2010, 07:44 PM

so in order for the rpm's to be accurate at longer distances did it need to be over stabilized at shorter distances ? would that not be considered" going to sleep "?

sagacious

10-14-2010, 04:40 AM

Some one check my math
7BR,
Your math is a worthy and valiant effort, and is to be commended. The rub inherent in the question, "What is the length of travel for one revolution at N distance" is that the question involves much more complicated math. One must calulate the amount of spin damping that the bullet undergoes, as this affects the rate the bullet rotates at, and thus the distance over which it makes one full rotation. The rate of spin (ros) is constantly slowing from it's initial rate, and the ros at distance is dependent on the rate of spin damping. The rate of spin damping predicates on the atmospheric conditions, the surface geometry of the bullet, velocity, and the relationship of inertial dynamics to fluid flow over the bullet.

What most shooters do is only worry about initial rpm at the muzzle, same as most shooters only measure velocity near the muzzle.... and then test for performance at target.

Regards, and good shooting. :drinks:

44man

10-14-2010, 09:19 AM

so in order for the rpm's to be accurate at longer distances did it need to be over stabilized at shorter distances ? would that not be considered" going to sleep "?
Yes, that's the way I take it. Like I explained, actually watching bullets showed some very strange things but it can't be done with high power rifles, etc. Darn boolits need to be large enough and slow enough to see.
Some say they see a vapor trail from rifle bullets like from a fighter going through the sound barrier but you can see trails from much slower plane wings too. Might depend on the moisture in the air.
Then can it also be the bullet has not yet gone to sleep and is spiraling? That would disrupt the air more.
The TC 30-30 I talked about was a strange puppy with the boolit going sideways and returning to the original aim point. The gun was deadly accurate at 100 yards and with a scope from sandbags I have a pile of nickels and pennies with holes in them. One day I ran out of gas checks so I left them off. Every single boolit would go through the paper sideways at 50 yards. The only thing I can figure is I changed the bearing surface, making the boolit shorter and no longer matching the twist for the velocity.
I would say I was shooting the boolit at the ragged edge of stability by too high a velocity and too much spin, yet it always hit what I aimed at taking into account the windage changes at different distances. Did the length of a gas check really take it out of stability? Would reducing velocity have fixed it so I would not need the GC? My friend wanted the gun so I sold it before finding out.
Anyway you see why I can't recommend twist rates for anything. Too many tiny things can change what works and even a 1/2" change in twist rate might go one way or the other.
I only like a rate that works in the velocity range of a caliber.
My thinking is always mechanical because at my age I can't remember how to add 2+2! :holysheep

Eutectic

10-14-2010, 11:15 AM

The last few posts seem to 'spin' off some to my thinking....

Here's an interesting paragraph from Lilja Barrels... Daniel Lilja wrote it in fact. Lilja is pretty well known for ACCURATE barrels. I know many use them at long range...

"It is interesting to note that this force, or overturning moment, acting on the bullet nose is greatest when the bullet first exits the barrel. If a certain bullet-barrel combination will stabilize a bullet at the muzzle, the bullet will remain stable for the rest of its flight. Why is this so? As a bullet flies on toward the target and beyond, it is losing velocity rapidly as any trajectory table will show. For example a 68 grain bullet from a 6PPC leaving the barrel at 3150 fps will be going 2786 fps at 100 yards and 2449 fps at 200 yards (ballistic coefficient of .265 and standard metro conditions). The rotational speed of the bullet or its RPM's decreases at a much slower rate. The overall result is a lessening force acting on the bullet nose, and that force is being overcome by a proportionately greater spin rate compared to forward velocity. The down-range bullet therefore is more stable than it was at the muzzle. The only exception to this occurs when the bullet passes through the speed of sound. At that velocity, about 1180 fps, it may lose stability."

The full article can be seen here:
http://www.riflebarrels.com/articles/bullets_ballastics/effects_altitude_temperature_rifling_twist.htm

I found this paragraph in another paper 'deep' and interesting as well...

"As the projectile flies downrange, it attains an “over-spun”condition. At launch, the flow near the rifling grooves is essentially parallel to the grooves as a result of the no-slip boundary condition as shown in Figure 1. However, as the projectile flies downrange, the projectile’s forward velocity slows faster than the projectile’s spin rate, such that the nondimensional spin rate (pD/V) increases. This causes the flow near the grooves to be no longer aligned with the grooves(shown in Figure 1), producing an “over-spun” state. It is suspected that the over-spun condition downrange results in a change in the aerodynamic characteristics of the projectile."

Full write-up here:
http://pdf.aiaa.org/preview/CDReadyMAFM06_1306/PV2006_6009.pdf

Worth pondering on in my opinion.

Eutectic

Larry Gibson

10-14-2010, 11:46 AM

44man

Pitch and yaw are common in well stabilized bullets at close range. Many times they are induced by "over stabilization". When they "iron out" is what is refered to as "going to sleep".

There are varying degrees of stabilization as with any bullet there is a wide RPM range between minimally stabilized, stabilized and over stabilized. It is best to have the bullet in the "stabilized" range of RPM at the beginning of flight. Your example of the .44 bullets in the S&W (should have had an 18 3/8" twist) are a good example. At the velocity the lighter weight bullet was overstabilized and the heavier bullet was stabilized, both for the velocity they were at.

If we shoot cast bullets in the "stabilized range" the bullet should remain stabilized over the expected distance of flight. Thus stabilized most all bullets will remain stable long after the maximum range at which we shoot them is reached. If a bullet would go unstable from lack of velocity and/or too much RPM at 2000 yards does it matter if we only shoot 300 yards and the bullet has already been stopped in the berm? What we want for the best accuracy is the best stabilization across the range that we shoot at. What it might do beyond is moot.

In the case of 160 - 220 gr cast bullets in the '06 with 10" twist the optimum velocity for the "stabilized" range is 1600 - 1950 fps. If we have the same bullets in a 12" twist then the "stabilized" range moves to 1900 - 2300 fps. If you do the math the RPM is pretty much the same for both ranges.

Having the ability to actually measure the TOF and BC of a bullets flight over 100 yards gives us the measurement of a bullets stabilization. The less the TOF and the higher the BC the more stabilized the bullet is. I also have several .308W cal rifles with 9.5, 10, 11, 12 and 14" twists and several .223 rifles with 7, 9, 11, 12 and 14" twists. It is easy to measure a bullets stability, given a relatively equal velocity, out of those and determine which twist is best stabilizing that particular bullet.

Larry Gibson

Bass Ackward

10-14-2010, 01:00 PM

I would not forget his comment 'go to sleep'....... But what is it?????

Eutectic

I find this is the very biggest key to most shooting. It translates out to it's all in the launch.

Launch perfectly and muzzle pressure affects the launch uniformly (no yaw) and shooting variables are minimized to get a slug to travel through air accurately without the need to be spun faster. Which is why some guys / guns can achieve more.

Twist rate compensates for error or ignorance making experts of everyone right up until the point bullet material fails to launch well for what ever the reason.

Three-Fifty-Seven

10-14-2010, 03:00 PM

I will apologize in advance . . .

Borderline Stabilization... at long range - Yeah we need some more of that down here in AZ!:mrgreen:

:Fire:

:coffee:

Eutectic

10-14-2010, 05:36 PM

I will apologize in advance . . .

Borderline Stabilization... at long range - Yeah we need some more of that down here in AZ!:mrgreen:

:Fire:

:coffee:

You brought a grin to my face.... It didn't last though...... I grieve for you folks down there close to this mess.

I am ashamed of this Administration for sitting on their prat on this! Where's a "Black Jack" Pershing when you need him!

Sorry for the rant........ Eutectic

Dannix

10-14-2010, 11:30 PM

I found this paragraph in another paper 'deep' and interesting as well...

"As the projectile flies downrange, it attains an “over-spun”condition. At launch, the flow near the rifling grooves is essentially parallel to the grooves as a result of the no-slip boundary condition as shown in Figure 1. However, as the projectile flies downrange, the projectile’s forward velocity slows faster than the projectile’s spin rate, such that the nondimensional spin rate (pD/V) increases. This causes the flow near the grooves to be no longer aligned with the grooves(shown in Figure 1), producing an “over-spun” state. It is suspected that the over-spun condition downrange results in a change in the aerodynamic characteristics of the projectile."

Full write-up here:
http://pdf.aiaa.org/preview/CDReadyMAFM06_1306/PV2006_6009.pdf

Experimental Determination of the Effect of Rifling Grooves on the Aerodynamics of Small Caliber Projectiles
"This material is declared a work of the U.S. Government and is not subject to copyright protection in the United States."

I found the whole paper, but it's "payware" despite the non-copyright status.
http://www.aiaa.org/content.cfm?pageid=406

Anyone have the contact info for:

Sidra Silton, Weapons and Materials Research Directorate, ARL, Aberdeen Proving Ground, MD; David Webb, Weapons and Materials Research Directorate, ARL, Aberdeen Proving Ground, MD
AIAA-2006-6009
AIAA Atmospheric Flight Mechanics Conference and Exhibit, Keystone, Colorado, Aug. 21-24, 2006

Otherwise, anyone interested in a "group buy" to defray the costs for the non-copyrighted material?

Edit: I found the email address for David Webb. I'm going to shoot him an email.

Dannix

10-14-2010, 11:52 PM

"It is interesting to note that this force, or overturning moment, acting on the bullet nose is greatest when the bullet first exits the barrel. If a certain bullet-barrel combination will stabilize a bullet at the muzzle, the bullet will remain stable for the rest of its flight. Why is this so? As a bullet flies on toward the target and beyond, it is losing velocity rapidly as any trajectory table will show. For example a 68 grain bullet from a 6PPC leaving the barrel at 3150 fps will be going 2786 fps at 100 yards and 2449 fps at 200 yards (ballistic coefficient of .265 and standard metro conditions). The rotational speed of the bullet or its RPM's decreases at a much slower rate. The overall result is a lessening force acting on the bullet nose, and that force is being overcome by a proportionately greater spin rate compared to forward velocity. The down-range bullet therefore is more stable than it was at the muzzle. The only exception to this occurs when the bullet passes through the speed of sound. At that velocity, about 1180 fps, it may lose stability."

The full article can be seen here:
http://www.riflebarrels.com/articles/bullets_ballastics/effects_altitude_temperature_rifling_twist.htm

I made a PDF of this one but it's just a bit too big to attach. Posterity -- shoot me a PM if this link ever dies.

On another note, lots of really cool stuff was discussed at YPSE-06:
http://www.aiaa-baltimore.org/YPSE-06/Titles.shtml

44man

10-15-2010, 10:37 AM

Eutectic

10-15-2010, 12:18 PM

44man, Larry....

It seems S&W used to put 1 in 18 3/4" twist in everything from .32 to .44 caliber for their revolvers.
Smith .44's have shot pretty well for me with cast... But it isn't my most accurate .44. That spot goes to a Colt Single Action Army in .44 Special. The twist is 1 in 16" ??
I have a super accurate K-38. Super accurate using 148gr hollow base wadcutters. Does almost as well with 125gr cast. 158gr loads display yaw at the target and 2" groups become its performance at 25 yards.
A friend has a Colt Python .357..... IT IS ACCURATE! We shot 158gr Semi-wadcutter loads one day loaded down in .357 cases to about 850fps. They would touch each other at 25 yards.... The Python has a twist of 1 in 14".
Years ago, I shot competition with an old gentleman that had a Colt Officers' Model target revolver in .38 Special... Very accurate... I wish he was still with us as I'd like to test more 38 Special loads in Colt's 1 in 14" against S&W's 1 in 18 3/4"...

I tend to agree with the thought of a 'little tighter' twist in some of my revolvers.

Eutectic

Cap'n Morgan

10-15-2010, 03:30 PM

The last few posts seem to 'spin' off some to my thinking....

Here's another spin-off - so to speak: Spinning .40 cal bullet on ice
http://www.youtube.com/watch?v=foZlciP6gUQ

At first i thought "No way!" but it actually seems to be a real phenomenon.

44man

10-15-2010, 03:53 PM

Here's another spin-off - so to speak: Spinning .40 cal bullet on ice
http://www.youtube.com/watch?v=foZlciP6gUQ

At first i thought "No way!" but it actually seems to be a real phenomenon.
That was a fun thing. Must be awful hard ice too. Notice the bullet was not melting the ice.

herbert buckland

10-15-2010, 05:36 PM

Larry Gibson

10-16-2010, 12:13 AM

Larry Gibson

10-16-2010, 12:18 AM

the fast twist in pistols seems to go against the formular for twist rates.My experince with short bullets has shown they will not be acurate in fast twist rifle barells,I have found that bullet lenth and slowing velocity is the only way you can get a 50ca BP rifle to shoot with a 1 in 20 twist rate,why is this difrent in a pistol

It's not "different" in a pistol. Most would shoot the shorter, lighter bullets better out of slower twists if the velocity got high enough. Ooooops, might be why the shorter, lighter pistol bullets shoot better out of the slow twist carbines and rifles.

Larry Gibson

44man

10-16-2010, 03:13 PM

It's not "different" in a pistol. Most would shoot the shorter, lighter bullets better out of slower twists if the velocity got high enough. Ooooops, might be why the shorter, lighter pistol bullets shoot better out of the slow twist carbines and rifles.

Larry Gibson
Again this is correct. What many fail to think about is pistol barrel length versus twist. It still depends on the velocity you can achieve so a 4" is not as good as a 10" with the same twist and load. Also the other way around.

herbert buckland

10-16-2010, 06:43 PM

Larry Gibson

10-16-2010, 08:41 PM

Other things contribute to inaccuracy in rifles vs handguns. The use of a magnum load in a rifle for instance. Many times the PB cast bullets that shoot fine out of the handgun produce too much velocity out of the rifle for good accuracy. Has to do with the limitations on the PB. Shooting magnum loads with Kieth bullets cast of WWs + 2% tin at 1400 fps out of a 6.5" barreled revolver produce 1600+ fps out of a 10" Contender and 1800+ out of a 20" rifle. Accuracy is excellent out of the revolver yet poor with the Contender and rifle unless I back the velcocity off to 1400 - 1500 fps. However, load a GC'ed SWC (429244) with the same magnum load and it shoots very well in all 3 firearms. Not the twist there, just the limitations of a PB bullet. Cast the Kieth bullet really hard and accuracy can be good in the Contender but just ok in the rifle.

Larry Gibson

44man

10-17-2010, 02:15 PM

It still does not make sence to me when I checked the optum stability for a .684 long .429 groove diameter 240gr 44magnam traveling at 1000fps it stated that the twist rate should be 1-29.8,and from experince I know that a faster twist in a rifle (same caliber ,same velocity gives terible acuracy)am I missising somthing
The problem is that you are reading and not testing.
What .44 rifle do you have that has a faster twist then a revolver? Most .44 rifles are too slow with 1 in 38" twist.

felix

10-17-2010, 02:39 PM

That's correct, 44man! Latest issue Ruger rifles are 20 twist; Winchester rifles 26 twist. ... felix

herbert buckland

10-17-2010, 07:00 PM

The problem is that you are reading and not testing.
What .44 rifle do you have that has a faster twist then a revolver? Most .44 rifles are too slow with 1 in 38" twist.I am testing that is why I can not make sence of it .The rifle tested was a Uberty 44-40 with a 1 in 36 twist rate ,sluged at .429,I got very good acuracy with it at 100 meters yousing a 200gr bullet at 1200fps.Now to be so I could judge the diffrence twist rates make I loaded My 44magnum super blakhalk revolver so the velocity was 1200fps,acuracy was terible with the faster twist rates,I then loaded 240gr,270gr &300gr bullets in it trying to stay close to the same velocity,results were the longer the bullits the better the acuracy as I expected,the only way I could get the shoter bullets to shoot was drop the velocity,so my conclusion is (I am proberly wrong) is if you want to have acuracy with a 44magnum with 240gr bullet the twist rate has to be changed to a slower rate or you drop the velocity(which does not work on the 300meter rames)all bullets were plain bass hard cast,the fast twist rifles that I tested were a Armi Sports 44 Rusian with a 1 in 16 twist ,a Armi Sports 45 colt with the same twist ,acuracy was terible till the velocity was droped to 300fps,and to be fair to Armi Sports I tryed there 44-40 with a 1 in 36 twist(in my opinuion the proper twist rate for this cartridge)and it was very acurate

Good Cheer

10-17-2010, 08:15 PM

Google this...
Reports_of_Experiments_with_Small_Arms_f

It's a copy of an 1850's US gov report on small arms development. It includes info on the spin causing the curve at long range.

44man

10-18-2010, 09:47 AM

That's correct, 44man! Latest issue Ruger rifles are 20 twist; Winchester rifles 26 twist. ... felix
Both will work but it is just too late for my Marlin, darn it anyway, some seen the light! :???:

44man

10-18-2010, 10:21 AM

I am testing that is why I can not make sence of it .The rifle tested was a Uberty 44-40 with a 1 in 36 twist rate ,sluged at .429,I got very good acuracy with it at 100 meters yousing a 200gr bullet at 1200fps.Now to be so I could judge the diffrence twist rates make I loaded My 44magnum super blakhalk revolver so the velocity was 1200fps,acuracy was terible with the faster twist rates,I then loaded 240gr,270gr &300gr bullets in it trying to stay close to the same velocity,results were the longer the bullits the better the acuracy as I expected,the only way I could get the shoter bullets to shoot was drop the velocity,so my conclusion is (I am proberly wrong) is if you want to have acuracy with a 44magnum with 240gr bullet the twist rate has to be changed to a slower rate or you drop the velocity(which does not work on the 300meter rames)all bullets were plain bass hard cast,the fast twist rifles that I tested were a Armi Sports 44 Rusian with a 1 in 16 twist ,a Armi Sports 45 colt with the same twist ,acuracy was terible till the velocity was droped to 300fps,and to be fair to Armi Sports I tryed there 44-40 with a 1 in 36 twist(in my opinuion the proper twist rate for this cartridge)and it was very acurate
Only a few of your observations are right. The SBH with a 240 gr bullet needs more velocity and the XTP needs 24 gr of 296, the Hornady silhouette bullet is better with 23.5 gr.
1200 fps is too slow.
The 270 cast would work with 22 gr and the 300 cast might be better with 22 also. The 320 gr cast is best with 21.5 (1316 fps) and the 330 cast uses 21 gr.
These are based on the Fed 150 primer. Now be careful because the heavier boolits from 270 to 330 gr are CAST so if you use a 300 gr XTP you only need 20.5 gr of 296. I can't tell you what load to use for a 270 gr jacketed.
The SBH does NOT like light bullets under 240 gr.
You can't compare the 44-40 to the .44 mag. You are too confused over twist rates because you are working with other calibers with vast velocity differences and boolit weights. You are also trying rifles and revolvers expecting the same results from the same loads and bullets.

BABore

10-18-2010, 02:49 PM

The SBH does NOT like light bullets under 240 gr.

Huh!
This is at 50 yards. Ruger SBH Hunter, 7 1/2", Leopold 2x scope.

At 385 yards this 200 grain HP boolit groups into around 4 1/2 inches. Multiple groups, fired by 45 2.1 and myself. Witnessed by several other board members. Alloy was 50/50 WW-Pb air cooled, 10 bhn. Fast powder too.

In yer eye 44Man. :bigsmyl2:

45 2.1

10-18-2010, 02:53 PM

Huh!
This is at 50 yards. Ruger SBH Hunter, 7 1/2", Leopold 2x scope.

At 385 yards this 200 grain HP boolit groups into around 4 1/2 inches. Multiple groups, fired by 45 2.1 and myself. Witnessed by several other board members. Alloy was 50/50 WW-Pb air cooled, 10 bhn. Fast powder too.

In yer eye 44Man. :bigsmyl2:

Yep, it's true Jim......... That little hollow point boolit shoots quite well in the 44 Special handguns and 44 Mag rifles also. Sure suprised Mikey what could be done with a handgun.

herbert buckland

10-18-2010, 06:13 PM

I do no think I am confusing anything by by yousing diffrent calibers if they have the same groove diameter and they are going through the cronagrafh at the same speed (the only varible is the twist rate)a bullit of the same shape,weaight& velocity after it has left the barell ,the only difrence is RPM,so how come pistols have a fast twist rate when it is clear that the same bullet at the same velocity has no acuracy in a rifle,and as for hollow points this is working on the old British express rifle system(bullet is still long so it can be yousedin faster twist barells,but weaight is droped so you can get higher velocity)I am not trying to start a argument ,I just think a lot of pistols have twist rates that are too fast for best acuracy,and have had no one explain why they have such fast twist rates,there must be a reason

mpmarty

10-18-2010, 06:41 PM

No, it travels slightly further than 14" to complete a full revolution, because the ros at distance has slowed from the rot at muzzE
If the velocity decreases faster than the ros then the bullet will make a 360 degree rotation in LESS than 14 inches of travel.

Larry Gibson

10-18-2010, 08:57 PM

If the velocity decreases faster than the ros then the bullet will make a 360 degree rotation in LESS than 14 inches of travel.

That it correct. However, the RPM has already been established by the rate of spin and the muzzle velocity. The RPM then slows down very little over the practical flight of a bullet. The RPM is not based on any remaining velocity down range.

Larry Gibson

44man

10-19-2010, 08:58 AM

Yep, it's true Jim......... That little hollow point boolit shoots quite well in the 44 Special handguns and 44 Mag rifles also. Sure suprised Mikey what could be done with a handgun.
I guess I can't say that anymore, can I? :bigsmyl2::bigsmyl2:
Must be a good boolit, I never had luck with the few I borrowed.
I had to think about it a little. Is the hollow point boolit a little longer in length? Since it is not actual weight that governs stability.
A picture of one next to a 240 gr might tell a lot.
I did get some 220 gr boolits to shoot good so if they were drilled out, they might still be a decent length for the rifling.
No, I am not giving up entirely yet! :drinks:
180 gr bullets drove me nuts. The tightest groups I ever shot from most .44's was always with the 240 XTP. Next is the Hornady 240 silhouette and last is the Speer. Speer no longer lists the same bullet, they are now mags or Gold Dot's.

Eutectic

10-19-2010, 12:43 PM

I have read Mann's book "The Bullet's Flight" all through. Thanks again trk and c3d4b2!
It is the type of book I love as it is so full of detail! But like a tough piece of steak; many areas have to be gone back over and over.... 'chewed' again and again!
It is amazing what Mann accomplished without a computer or high speed photography! Much less a ballistics' lab! The poor guy didn't even have a calculator! Yet his 'screens' (or paper prints) of bullet strikes are absolutely amazing for the amount he learned from them. I WAS INTRIGUED AS WELL AS MOVED, by his rate of spin experiments by filing the bullet's nose shape.

This same testing I plan to continue on with.. over a century later......

We speculate, assign acronyms, even guess, in this thread on downrange dynamics of our bullet's 'spiral'.... (This is Mann's word.... He stated 'helix' wasn't used as 'spiral' was a "more accepted terminology". Imagine that.......
Carefully examining exactly how our bullet makes one 360 degree rotation over "x" distance downrange will certainly help us know where the 'bear xxxx in the buckwheat' to put it nicely.....
I might add Mann finds a 'compressed helix'; oops, sorry..... Mann finds bullets making full 360 degree rotations downrange IN LENGTHS LESS THAN THE BARREL'S TWIST THEY WERE SHOT FROM!
If Mann's 'wedge' pointed bullet modification shoots accurate enough downrange; I plan to measure (at extended range) the bullet's 'one 360 degree rotation length' in real life fact... NOT THEORY!

The boolit nose 'prints' nicely. (better than I expected) Take a look... I will begin at 15 feet for a baseline length for a 360 degree rotation them move my 'screens' out farther and see what happens....

Eutectic

http://www.hunt101.com/data/500/wedgehead_revolution_counters2.jpg

Eutectic

10-19-2010, 09:00 PM

Some preliminary testing accomplished today.......

I chose a Savage Model 340 in .30-30 for several reasons. First, although the title of this thread refers to 'Borderline Stabilization' I didn't want that yet.. It would be another variable in my primary goal of testing and finding "x" length of forward travel for our boolit to achieve one 360 degree rotation.
This gun is accurate with cast boolits... it is scoped... I have a bunch of commercial cast 311041 clones that shoot OK but not great. The gun has 1 in 12" twist and is close to that as I have measured it before. So I started by measuring the twist...
A 1/4" dowel cleaning rod was used that had a centerline marked down its length longitudinally. I marked a perpendicular line across the centerline and another 12" further down measured by a 12" machinist rule.
There is quite a knack to pushing a tight patch through a bore and getting an accurate reading for twist. You have to apply some torsion with the twist as you push.... but not too much! Not too little either or you will get slippage... I usually measure about a dozen times and take an average. My longest reading and my shortest reading will usually be 1/8" or so off the average. With all that I called the 340's twist 12 1/16" in this .30-30 barrel...
I shot this 12 1/16" paper spacing at 15 feet and I was very close. Careful testing had the actual rotation length at 12.1".
The first detriment showed its ugly face. The 'wedgehead' modification to the boolit wasn't very accurate. (I used 2000fps MV) My apparatus for holding the paper only has a 3 1/2" square 'shooting window'. The most I can safely shoot in my backyard is 75 yards... Even so, this un-balanced bullet would be a maybe thing. So I modified some boolits as Mann had done on his first 100 yard rotation test. They basically have a flat filed into one side of the point and make a print like this....
http://www.hunt101.com/data/500/rotation_counter.jpg

This different boolit modification allowed me to complete the 75 yard test. The "x" value averaged 11.4" travel for one complete 360 degree rotation!

These preliminary results confirm my thoughts and were Franklin Mann's as well over 100 years ago.

Most of the modified boolits display 'yaw' at 75 yards. Mann calls this oscillation and I like his word better. A bullet nose that marks its 'spot' and is balanced (as least better balanced) is what I need!

Now, I will build a 'screen holder' for a larger target. I plan to slow the load down to 1800fps to help the un-balanced boolit and try for better accuracy.. First though, I have a couple thoughts to test for a 'point marker' on the boolit that is more balanced.. Better accuracy will really help as I stretch out the yardage. I really want to see what the "x" length value becomes at several hundred yards out! I really don't want a 3 foot square for a target either as it would be murder to keep accurate for spacing between sheets as well as uniformly square over the large surface area.

Eutectic