Twist rate -- Apparently dependent on velocity, not just projectile weight

[Dannix]

Well go figure. I came across the graph on this thread (http://www.ar15.com/forums/topic.html?b=3&f=16&t=491888&page=1). I've heard Molon has some outstanding threads there. I've been meaning to dig into them, but I happened to come across this just now and wanted to share. Seems time goes by oh so too quickly when trying to read up on great info. :groner: The more I learn, the more I realize how much I don't know.

[44man]

Nice chart! [smilie=s:
Now we need them for revolvers too. Seems as if everyone forgets they have rifling and all lengths of barrels. Some stuff can't be shot with accuracy. Like a 320 gr .44 boolit at 700 fps from a 4" barrel! :veryconfu

[pdawg_shooter]

The faster the fps the more rpms. Length and velocity are the main factors.

[Rocky Raab]

Barrel length should have nothing to do with it, except insofar as it affects muzzle velocity.

Velocity and bullet length are the only two factors determining bullet stability.

BTW, you can figure the RPM of a bullet with the simple formula: twist/12 x 60 x velocity

To make the concept clear, a bullet moving at one foot per second in a 1-12" bore spins at one turn per second, or 60 rpm. At 1000 fps, it spins 1000 time faster, or 60,000 rpm, and so forth.

[Larry Gibson]

Yes, a certain amount of RPM is needed for a bullet to be stable. However we need to remember that stability, while required for accuracy is not a guarentor of accuracy. Note the accuacy difference between milsurp ball ammo and commercial or match ammo in numerous cartridges. All are stable but the accuracy depends on the quality of the bullet (balance) and the amount the stabilization (RPM) affects the external filight of the bullet. There indeed can be not enough, just right or too much stabilization.

Larry Gibson

[45 2.1]

Velocity and bullet length are the only two factors determining bullet stability.

Thats news.......... how about shape? Lots of difference between a cylinder (known as a wadcutter) and a 6 caliber ogive (usually on a match bullet).

[montana_charlie]

I haven't learned anything new about .223 bullets since I turned in my M-16 in 1972.
But, I'm pretty sure that 64 grains is considered 'heavy' for the caliber.

If a person didn't think about it much, he could get the idea that all .223 bullets of 64 grains fired in a 9 twist will need 4000 fps for stability. While that may be true more often than not, it isn't written in stone...and the chart only applies to one bullet design.

Since the charted bullet does require a full 4000 fps for optimal stability, I bet it is a long ogive shape with a large portion of it's weight in the rear. A bullet of the same weight with a shorter nose would move the center of gravity forward...and not require quite so much rpm for stability. Therefore, it would work well at lower velocity.

CM

[Rocky Raab]

45 2.1, nope. Length is the only bullet factor. That's why a roundnose will often be more accurate than a pointy bullet of the same weight: It is shorter and therefore slightly more stable at a given velocity.

Or, the flip side of it: A long bullet has to be driven faster at a given twist rate to be stable, compared to a shorter bullet of the same weight.

[felix]

Correct, Rocky. The more wind resistance, front (meplat) and sides (length), the more twist is needed. The wind factor diminishes dramatically for shorter target distances. This is why a full wadcutter works at 50 yards with the proverbial twists for the caliber. Put a hat on the wadcutter, and the projectile will make a hunnert before all goes to pot. The cap size/shape will allow the variance in the yardage obtained with acceptable accuracy. Actually, the nose of the Keith acts as a well designed cap for the wadcutter. ... felix

[45 2.1]

45 2.1, nope. Length is the only bullet factor. That's why a roundnose will often be more accurate than a pointy bullet of the same weight: It is shorter and therefore slightly more stable at a given velocity.

Or, the flip side of it: A long bullet has to be driven faster at a given twist rate to be stable, compared to a shorter bullet of the same weight.

You really need to do some testing.....................

[44man]

Barrel length should have nothing to do with it, except insofar as it affects muzzle velocity.

Velocity and bullet length are the only two factors determining bullet stability.

BTW, you can figure the RPM of a bullet with the simple formula: twist/12 x 60 x velocity

To make the concept clear, a bullet moving at one foot per second in a 1-12" bore spins at one turn per second, or 60 rpm. At 1000 fps, it spins 1000 time faster, or 60,000 rpm, and so forth.
That is the problem, can you reach velocity and RPM's? Some think so by going to a fast powder and ruining the boolit trying to match the velocity from a longer barrel and slower powder by punching the boolit all at once.
Everyone knows that the longer the barrel, the faster any load will be until powder push is exhausted, then the boolit will slow from air resistance and friction.
But take my example of a 320 gr boolit at 700 fps from the .44. There is no way to stabilize it with any barrel length. Now increase the velocity to about 1350 and it is extremely accurate but it is going to take a slow powder and a longer barrel to meet the requirements. That might be 6" to 7-1/2" or even 10". To try and get to that velocity with a 2" or 4" barrel is asking too much.
The twist has not changed but what you can put down it sure does.
Now what would happen if as barrels get shorter, a faster twist is used?
I have seen no work done with this. What if your 30-06 is perfect with your bullet and load out of a 24" barrel with 1 in 10". What would shortening the barrel to 20" do? Maybe a 1 in 9" would work as good as the longer barrel.
Rifles are easier because you have a range of powders but in a revolver you quickly run out of compatible powders. Then you get into slump, boolit damage and skid. You also have to think of high pressure gas exhaust at the muzzle and boolit base as it leaves.
The work I have done with a 10" 45-70 that has a 1 in 14" twist was very, very difficult. Then some cowboy wants to cut the gun to 4". :bigsmyl2: HELLO!

[Dannix]

Rocky Raab
What I found fascinating though is that there's an inversion area -- where stability got better with LESS RPM I also found it interesting that the stability feel off a cliff between 1150 and 1100 fps. Such a dramatic change with just a 5% drop in velocity surprised me.

Larry Gibson
Your comment about bullet quality makes sense. The comment about too much stablitzation reminds me of this info from a Cheytac whitepaper. (http://castboolits.gunloads.com/showpost.php?p=1025908&postcount=44)
http://castboolits.gunloads.com/attachment.php?attachmentid=26031&d=1286939168


montana_charlie
77gr is as heavy as AR can go at this caliber, but requires a 1:7 twist barrel. I haven't really looked at any other weight/twist combinations. If I recall correctly though, 1:9 is the old standard and 69gr is considered the maximum weight for that twist, but don't quote me on that.

[Rocky Raab]

Bullet shape has an effect on its aerodynamics, but not directly on stability. It is true that a marginally stable bullet can be tumbled by aerodynamic forces, but that is not the same thing as saying its shape makes it unstable. Air is a substance, and just as some bullets will tumble if they encounter a stem of grass, so will some bullets tumble when they hit air - but that has little if anything to do with the bullet's shape. A bullet with positive stability created by its spin versus length will resist being affected by EITHER kind of substance.

[Dannix]

Thats news.......... how about shape? Lots of difference between a cylinder (known as a wadcutter) and a 6 caliber ogive (usually on a match bullet).


Since the charted bullet does require a full 4000 fps for optimal stability, I bet it is a long ogive shape with a large portion of it's weight in the rear. A bullet of the same length with a shorter nose would move the center of gravity forward...and not require quite so much rpm for stability. Therefore, it would work well at lower velocity.

45 2.1, nope. Length is the only bullet factor. That's why a roundnose will often be more accurate than a pointy bullet of the same weight: It is shorter and therefore slightly more stable at a given velocity.

Or, the flip side of it: A long bullet has to be driven faster at a given twist rate to be stable, compared to a shorter bullet of the same weight.

Weight, Length and Ogive/nose .... I'm trying to boil this down -- Is it really all about centre of gravity? My thinking is the farther back the centre of gravity, the less "tail" there is to damp out yawing. In fact the "tail" aspect made me crack open my jeppesen ground school book. They refer to it simply as directional stability. The way I'm reading this, the projectile needs to have enough directional stability to overcome the yaw resulting from gyroscopic precession. Makes sense, expect the gyroscopic stability aspect isn't considered as airplanes aren't shot out of a rifled barrel. And some instability is desired in an airplane so it is manoeuvrable, something not desired for a free-flight projectile.

Let me ask this: Ceteris paribus, does bearing surface matter in regards to needed twist rate and velocity to be stable when airborne?


Correct, Rocky. The more wind resistance, front (meplat) and sides (length), the more twist is needed. The wind factor diminishes dramatically for shorter target distances. This is why a full wadcutter works at 50 yards with the proverbial twists for the caliber. Put a hat on the wadcutter, and the projectile will make a hunnert before all goes to pot. The cap size/shape will allow the variance in the yardage obtained with acceptable accuracy. Actually, the nose of the Keith acts as a well designed cap for the wadcutter. ... felix
Interesting post felix and demonstrates there's more too it than center of gravity. I haven't figured figured out why full wadcutters become unstable. "Extreme" meplat designs e.g. Gate's, are apparently fine. Correct me if I'm wrong, but there's nil testing of full wadcutters beyond subsonic, correct? This inclines me to consider the tail. I wonder if a backwards semi-wadcutter would be stable. That said, semi-wadcutters and extreme meplat FNs must alter the pressure wave just enough.

[pdawg_shooter]

Rocky Raab
What I found fascinating though is that there's an inversion area -- where stability got better with LESS RPM I also found it interesting that the stability feel off a cliff between 1150 and 1100 fps. Such a dramatic change with just a 5% drop in velocity surprised me.

Larry Gibson
Your comment about bullet quality makes sense. The comment about too much stablitzation reminds me of this info from a Cheytac whitepaper. (http://castboolits.gunloads.com/showpost.php?p=1025908&postcount=44)
http://castboolits.gunloads.com/attachment.php?attachmentid=26031&d=1286939168


montana_charlie
77gr is as heavy as AR can go at this caliber, but requires a 1:7 twist barrel. I haven't really looked at any other weight/twist combinations. If I recall correctly though, 1:9 is the old standard and 69gr is considered the maximum weight for that twist, but don't quote me on that.

Your 1100 to 1150 fps falls into the trans-sonic range. Strange things happen to bullets when they pass through the trans-sonic range. That is why long range shooters choose a cartridge that will launch the bullet fast enough to remain super sonic all the way to the target.

[Dannix]

Directional Stability, Gyroscopic Precession
http://i51.tinypic.com/10cruyd.jpg (http://img69.imageshack.us/img69/6140/directionalstabilty.jpg) http://i54.tinypic.com/2iaq5p4.jpg (http://img231.imageshack.us/img231/4851/gyroscopicprecession.jpg)

[Dannix]

Your 1100 to 1150 fps falls into the trans-sonic range. Strange things happen to bullets when they pass through the trans-sonic range. That is why long range shooters choose a cartridge that will launch the bullet fast enough to remain super sonic all the way to the target.
Good point! I guess I was in airplane mode, so was thinking in mph/knots.

[Rocky Raab]

Airplane mode doesn't work with bullets. Match bullets have hollowpoints to move the center of gravity behind the center of pressure - exactly the opposite of aircraft design. Why bullets are more stable that way is beyond my ken, but that's the way it is.

[Dannix]

Center of pressure for an airplane is center of 'lift' (with the plane as the frame of reference). CofG is in front for directional stability, and the horizontal stabilizer balances out what would otherwise be asymmetrical lift.

http://i56.tinypic.com/2a5gh6q.jpg (http://img208.imageshack.us/img208/4350/centerofpressure.jpg) http://content.answcdn.com/main/content/img/McGrawHill/Aviation/f0139-01.gif


Match bullets have hollowpoints to move the center of gravity behind the center of pressure
You got a source for that? It would surprise me if that's truly the case. I will freely admit I have much to learn in regards to gyroscopic stability however.

http://exploration.grc.nasa.gov/education/rocket/Images/rktstab.gif
http://exploration.grc.nasa.gov/education/rocket/rktstab.html








Velocity and bullet length are the only two factors determining bullet stability.
Thats news.......... how about shape? Lots of difference between a cylinder (known as a wadcutter) and a 6 caliber ogive (usually on a match bullet).
45 2.1, nope. Length is the only bullet factor.
Surely the nose plays a factor in the location of the CofP. Perhaps this is why full wadcutters behave they way they do -- they are initially stabilized but become unstablized once airborne.

[montana_charlie]

I believe you can take your airplane stuff and your rocket stuff and stick them in your 'bookcase'.

You already know that a bullet is only stable because it is spinning. I don't think any planes or rockets operate on that principle.

You waste your time (and ours) by trying to make them relate.

CM

[Dannix]

Barrel length should have nothing to do with it, except insofar as it affects muzzle velocity.

Velocity and bullet length are the only two factors determining bullet stability.

BTW, you can figure the RPM of a bullet with the simple formula: twist/12 x 60 x velocity

To make the concept clear, a bullet moving at one foot per second in a 1-12" bore spins at one turn per second, or 60 rpm. At 1000 fps, it spins 1000 time faster, or 60,000 rpm, and so forth.


That is the problem, can you reach velocity and RPM's? Some think so by going to a fast powder and ruining the boolit trying to match the velocity from a longer barrel and slower powder by punching the boolit all at once.
Everyone knows that the longer the barrel, the faster any load will be until powder push is exhausted, then the boolit will slow from air resistance and friction.
But take my example of a 320 gr boolit at 700 fps from the .44. There is no way to stabilize it with any barrel length. Now increase the velocity to about 1350 and it is extremely accurate but it is going to take a slow powder and a longer barrel to meet the requirements. That might be 6" to 7-1/2" or even 10". To try and get to that velocity with a 2" or 4" barrel is asking too much.
The twist has not changed but what you can put down it sure does.
Now what would happen if as barrels get shorter, a faster twist is used?
I have seen no work done with this. What if your 30-06 is perfect with your bullet and load out of a 24" barrel with 1 in 10". What would shortening the barrel to 20" do? Maybe a 1 in 9" would work as good as the longer barrel.
Rifles are easier because you have a range of powders but in a revolver you quickly run out of compatible powders. Then you get into slump, boolit damage and skid. You also have to think of high pressure gas exhaust at the muzzle and boolit base as it leaves.
The work I have done with a 10" 45-70 that has a 1 in 14" twist was very, very difficult. Then some cowboy wants to cut the gun to 4". :bigsmyl2: HELLO!
What's the twist for your .44?

I think it was Ruger who came out with a 20" .308 with a faster than normal twist. My impression was it was not well received, but then I don't remember who made the comment and perhaps Ruger had actually done their homework.

[Dannix]

I believe you can take your airplane stuff and your rocket stuff and stick them in your 'bookcase'.

You already know that a bullet is only stable because it is spinning. I don't think any planes or rockets operate on that principle.

You waste your time (and ours) by trying to make them relate.

CM
I'm sorry to waste your time CM. I think they do relate, and I took the time to take and post those images so everyone would be on the same page in regards to terminology used, both by me and Rocky Raab. I disagree that a bullet is only stable because it is spinning -- there's more to it; otherwise full wadcutters would not have the characteristics that they have. My goal is to get beyond simply the basic use-a-faster-twist-rate / push-it-faster / tinker-with-the-nose solutions. And why the inversion in the graph? It's easy to just tinker because bullets are orders of magnitude cheaper than rockets and planes, and firearms have been around for much longer as well. But I guess what it comes down to is inquiring minds want to know. The author of the site linked below even goes as far as to mention the Coriolis effect -- now that's getting really persnickety.



Airplane mode doesn't work with bullets. Match bullets have hollowpoints to move the center of gravity behind the center of pressure - exactly the opposite of aircraft design. Why bullets are more stable that way is beyond my ken, but that's the way it is.
I came across a a slew of info and found these tidbits. CPM is the author's abbreviation of centre of pressure. It would appear it is desirable for the CPM to be behind the CofG. I would be very interested in your source.

The Magnus force
The figure above assumes that the CPM is located behind the CG. Experiments have shown that this comes true for a 7.62 x 51 FMJ standard Nato bullet at least close to the muzzle in the high supersonic velocity regime. (source) (http://ffden-2.phys.uaf.edu/212fall2001_Web_projects/Isaac%20Rowland/Ballistics/Bulletflight/fig10.htm)

The Magnus moment
It can be easily shown that this is only true, if the centre of pressure of the Magnus force CPM is located behind the CG. The Magnus force destabilizes the bullet and increases the angle of yaw, if its centre of pressure is located ahead of the CG, which may come true in a specific velocity regime. (source) (http://ffden-2.phys.uaf.edu/212fall2001_Web_projects/Isaac%20Rowland/Ballistics/Bulletflight/fig11.htm) I need to spend some time perusing the material over there, but the Magnus moment sure looks like Gryroscopic Precession.


Best Regards

[44man]

Dannix, my .44, like most, is 1 in 20" and it will cover a wide range of boolits from 240 to 330 gr, where I stopped.
The Marlin is 1 in 38" and nothing works after 50 yards. With a lot of work I have had 5 shots touching at 50 but it was hopeless to keep minute of deer at 100. Over a long time I tried everything in it.
The Desert Eagle .44 is 1 in 18".
I don't know what my S&W 29's were but even though very accurate with a 240 gr bullet, you could watch the bullets through a spotting scope at long range shooting and see the bullets rotate around the flight path like a corkscrew. That caused a slight difference in the POI as ranges changed. Going to 250 gr bullets stopped it.
The Ruger .45 Colt is 1 in 16" but because it shoots slower, it works and will handle from 250 to 350 gr.
All the BFR revolvers on the average have fast twist rates.
.44 is 1 in 16"
.454 is 1 in 16"
.460 is 1 in 20"
.475 is 1 in 15"
45-70 is 1 in 14"
.450 is 1 in 14"
.500's are 1 in 15"
All of these can handle heavier boolits at lower pressures. Light boolits do not do as well, there is a lot of overlap and the fast twists are very easy to work with using a very wide range of boolits.
Nose shape has little bearing on stability over range. Everyone says a WFN will not be stable past 50 yards yet we shoot them to 500 meters with accuracy. A WLN, WFN, RNFP or maybe even a full wad cutter will be stable in the proper spin rate. The problem is always trying to make them loaf along without a match to the twist. There is still some overlap but a boolit still wants to be as close to it's perfect velocity as you can get it.
Take the .44 and try to shoot a 320 gr at 800 fps or a 180 gr at over 1500 fps and you will be way out of the ballpark.

[45 2.1]

Dannix, my .44, like most, is 1 in 20" and it will cover a wide range of boolits from 240 to 330 gr, where I stopped.
The Marlin is 1 in 38" and nothing works after 50 yards. With a lot of work I have had 5 shots touching at 50 but it was hopeless to keep minute of deer at 100. Over a long time I tried everything in it.

This business of twist on this forum is ridiculous......... the guns are what they are. Many people found out how to make them shoot everything out there. The Marlin 1:38 twist is a leftover from the original rimfire twists... but it still works with everything, providing you know how. You might actually try NOT squeezing the death out of a soft boolit and ruining it while trying to seat it....... it would work then.

[Wayne Smith]

OK, guys. To restate a simple question that may not have a simple answer - is it the total length of the bullet that is important in choosing a twist or is it the bearing length of the boolit?

[45 2.1]

To restate a simple question that may not have a simple answer -
is it the total length of the bullet that is important in choosing a twist Bullet/Boolit length has a direct relationship to stability, but is of minor importance except in unusual cases today as twists are standardised for bullet weights in use. When you go outside of these parameters, you will have to deal with proper twist factors.

or is it the bearing length of the boolit? Boolits need to fit from base of neck to throat engaugement for body plus some are fitted so that the nose engauges to point of meplat radius. All that depends on the fit of your chosen boolit to the gun you want to use it in. Most all boolits that fit are capable of FAR GREATER ACCURACY than you can manage to achieve.

[onesonek]

OK, guys. To restate a simple question that may not have a simple answer - is it the total length of the bullet that is important in choosing a twist or is it the bearing length of the boolit?

The old Greenhill formula was based on length with a velocity of around 1800 fps for those days artillery pieces, and is totally antiquated.
So length was the main factor back then,,,not so today.
Modern programs use center of mass and shape or ogive and meplat , while length is a factor, it is only relative to the projectile design and constuction characterisics. In the long run of modern ballistics,,it's nose shape that has the most bearing in twist rate. Velocity most certainly comes into play, and the GSF, but for the most part, understabilized is bad, over stabilized, it just takeslonger for the boolit/bullet to "sleep"
If this is questioned, call any barrel maker or those that write ballistic programs
They will tell you the same.
So to answer your question, bearing is tied to center of mass, but center of mass is calulated from length and nose shape. Length alone is only a part part of the equation.

[44man]

This business of twist on this forum is ridiculous......... the guns are what they are. Many people found out how to make them shoot everything out there. The Marlin 1:38 twist is a leftover from the original rimfire twists... but it still works with everything, providing you know how. You might actually try NOT squeezing the death out of a soft boolit and ruining it while trying to seat it....... it would work then.
Nope and you know I never do that. 4 years fooling with both the gun and every bullet, boolit made, even from .430" to .434" with every alloy, powder, larger expanders, no crimp, etc. The gun was no better then deer at 100 but you would still take a chance making a good hit. Ballard rifling .003" deep, now that is a joke in itself.
The barrel never leaded and had no tight spots.
Biomans micro groove shoots better. It was like trying to shoot long boolits from a 1 in 60" round ball gun, goes bang and makes smoke!
Twist is not ridiculous in any gun unless you like a smooth bore.
Or did you mean that cast doesn't need to spin? :kidding:
Then why did Marlin change the .444 to a 1 in 20" twist? Too many complaints because even the .444 could not spin up a boolit with enough velocity to hit anything with. I talked to Marlin and they sent me a copy of Greenhill!
I sold the Marlin to someone that is converting it, best thing I ever did! I do not work with rifles right now but we have a few Marlin 45-70 and 30-30 rifles shooting lights out with cast.
Did you know I shoot smaller groups with my .54 Hawken and a round ball at 200 yards with open sights then the Marlin .44 would do at 50 yards with a 9X scope? I call this a poor 5 shot group from a muzzle loader at 50.
But please come over and I have all kinds of .54 boolits for you to shoot from this rifle---I also have the billy club used to smack a guy that misses! [smilie=l: Oh yeah, the gun is what it is!

[44man]

Hey fellas, ream out all of your rifling, not needed, just fit the boolit tight. :holysheep:veryconfu:veryconfu:takinWiz:

[45 2.1]

Hey fellas, ream out all of your rifling, not needed, just fit the boolit tight. :holysheep:veryconfu:veryconfu:takinWiz:

Are you having fun AGAIN at everybodys expense Jim................. Dutch4122 has a target I shot with his 1894 44 Mag that is the equal or better than the one you just posted (5 shots at 50 yards). Load was a cast approximately 300 gr. boolit of my design at close to max. velocity shot over the iron sights that came with the gun. The target was witnessed by BABore and Dutch4122 along with a non forum member. I believe it was his hog load. How you can say what you do is beyond me.

[JSnover]

These twist threads are the worst.... The OP was misguided into thinking weight was important. When the diameter, length, configuration, velocity and twist have been figured out, bullet weight will determine the charge weight. Weight isn't relevant (IMO) until you get to the end of the equation.

[44man]

Are you having fun AGAIN at everybodys expense Jim................. Dutch4122 has a target I shot with his 1894 44 Mag that is the equal or better than the one you just posted (5 shots at 50 yards). Load was a cast approximately 300 gr. boolit of my design at close to max. velocity shot over the iron sights that came with the gun. The target was witnessed by BABore and Dutch4122 along with a non forum member. I believe it was his hog load. How you can say what you do is beyond me.
No, I don't doubt you at all. I call it a one in a million Marlin .44 though. Bioman has one that shoots very well but it is a micro groove, older gun. The only thing I can figure is that more lands and grooves has a better grip on a boolit.
Either that or I had "one of those" guns! :drinks:

[45 2.1]

No, I don't doubt you at all. I call it a one in a million Marlin .44 though. Bioman has one that shoots very well but it is a micro groove, older gun. The only thing I can figure is that more lands and grooves has a better grip on a boolit.
Either that or I had "one of those" guns! :drinks:

Must be a lot of those "one in a million Marlin .44 rifles" running around ...... i've shot close to 15 others that do the same thing at 50 and most will do under 1.5 MOA at 150 yds. when scoped. Most rifles have problems with stubby boolits when they go transonic. Marlins require some operator knowledge to make them shoot along with loading what they like.

[44man]

These twist threads are the worst.... The OP was misguided into thinking weight was important. When the diameter, length, configuration, velocity and twist have been figured out, bullet weight will determine the charge weight. Weight isn't relevant (IMO) until you get to the end of the equation.
This is true!
Since most of what I do is with revolvers, weight means little and with boolits close in configuration, the same powder charge works through a range of weights.
The only problem is when a boolit can not shot fast enough because it is too heavy for the caliber. Of course that makes the boolit longer and in most revolvers, it must be seated deeper. That is when you move from a special to a magnum.
Now look at close range rifle shooters. They want a slower twist because over spinning a boolit will not allow it to go to sleep until beyond the distance they shoot. That will open groups at, say 100 yards. Now shooting to 500 meters they would use a faster twist.
That is where the Marlin .44 falls apart, it is a close range shooter. 50 yard groups will tell you nothing about 100 or 200 yards.
Twist is overlooked too much, it is important and I would say more important with cast because most rifles are not shot as fast.
To think it means nothing in a revolver and you can shoot anything even when barrel lengths change is just plain silly. You shorten a barrel and you must either increase velocity or turn up the twist.
How I would love a .44 mag revolver shooter make the gun shoot with a 1 in 38" twist! :kidding:Maybe a round ball and 10 gr of BP! [smilie=2:

[Dutch4122]

I wish I still had that target, but it was shot in April of 2008 and was the victim of some spring cleaning in my shop last year. Every round fired in that group was touching; and they nearly were stacked on top of each other. The boolit was a Group Buy design by 45 2.1 that was cut by Lee. It was/is a C434-265-RF three crimp that actually weighs 280 grns lubed & checked with my wheelweight alloy. I size to .433" (bore slugs .431") and the load was 22 grns of H4227.

BABore has the 434640-GC design in his catalog and I will be trying that design this summer. Weight on that one is 280 grns as well. After seeing what the "640" nose design did at loooong range out of your .357 Marlin 1894 (360640-PB) Bob I think it is time to see what my .44 Mag 1894ss will do at longer range this summer with a better boolit. :D

[44man]

Must be a lot of those "one in a million Marlin .44 rifles" running around ...... i've shot close to 15 others that do the same thing at 50 and most will do under 1.5 MOA at 150 yds. when scoped. Most rifles have problems with stubby boolits when they go transonic. Marlins require some operator knowledge to make them shoot along with loading what they like.
Due to hundreds of posts about Marlin slow twists and poor accuracy and some other calibers also fall into this, maybe you could show your results and show everyone how to do it. There is not a person here that is not interested, me included.
Send me boolits and loads to try in Bioman's rifle since I got rid of mine.

[firefly1957]

There can be an effect on the bullets stability from barrel length It relates to the amount of pressure behind the bullet as it exits the barrel. Those gases do effect a bullet as they depart the muzzle and a very high pressure could require a little faster rifling to keep bullet on intended course. I have heard this as the reasoning behind a close quarters 5.56 NATO with 7 inch barrel not accurately shooting bullets over 55 grs. in weight. The person relating this to me said that the muzzle blast was less pleasant than a 50 BMG.

[DCM]

Please look at this and read the attached link.

http://castboolits.gunloads.com/showthread.php?t=107867

[Dutch4122]

Send me boolits and loads to try in Bioman's rifle since I got rid of mine.


PM sent.

[45 2.1]

BABore has the 434640-GC design in his catalog and I will be trying that design this summer. Weight on that one is 280 grns as well. After seeing what the "640" nose design did at loooong range out of your .357 Marlin 1894 (360640-PB) Bob I think it is time to see what my .44 Mag 1894ss will do at longer range this summer with a better boolit. :D

Do yourself a favor and get the all hollow point version with the big pin going down to the crimp groove.

[44man]

Please look at this and read the attached link.

http://castboolits.gunloads.com/showthread.php?t=107867
Much closer. It shows a 1 in 29" rate for my boolit. Someone here said a 1 in 22" to a 1 in 25" rate is better for the rifle in .44.
As boolit length gets shorter, the rate gets slower so the .44 would work better with a 180 gr down to a RB with the 1 in 38" rate.

[BABore]

Must be why I used a 200 grain boolit driven at top velocity for excellent 100+ yard accuracy. I never boxed myself into a corner convincing myself I needed a hard, heavy, 300 grain 44 mag boolit for a deer. Even a stoutly loaded 240-250 grain boolit shot very well.

[Bass Ackward]

There are other considerations that confuse the issue, especially with lead.

What is needed in the way of velocity and twist rate for a slug depends on how well a slug is launched. Which is why some 38 twist Marlin / bullet / operator combinations will work and why some won't.

So what many people get caught up in twist rate and velocity requirements generally factor down to the barrel length and rifling height they are using. What you can get away with is how well you launch it and LOWER muzzle pressure just about always helps there which means a longer barrel.

The longer the barrel, the more powders and the wider the hardness window. The lower the BC of the slug, the better you better launch it or the shorter your accurate range with anything will be and you will require more RPMs to compensate than the next guy.

[44man]

Exactly right Bass and is why I said a shorter barrel needs a faster twist.
My Marlin was short, not much more then a pistol with a stock.
Might be why there are so many arguments and differences between guns.
I have one boolit I designed long ago for IHMSA. It weighs 250 gr and has a 5/32" meplat, more of a spitzer. It is .775" long with a drive band of .435". It would poke almost one hole at 50 yards but nothing it could be shot with made it work at 100.
But it is just not a boolit I would ever hunt with even if it did shoot.
Anything that shoots good up close but goes to pot farther means it is not spinning enough.
But not only barrel length, the little .44 case just does not hold enough powder or pressure to reach the velocity needed. So a few more inches of barrel will still not turn a poor twist rate into a silk purse, it will just help a little.
So a guy gets 1-1/2" at 100 with his Marlin with a scope, isn't it strange I can beat that with my revolver and a red dot? Change the twist on the Marlin and it should do 2" or better at 200 and would do it with an even shorter barrel then the one I had.
I will forever believe in twist that is proper first.
Look at my 45-70 revolver! It will shoot ANYTHING I put through the 1 in 14" twist. Most of these will do under 1" at 100.

[44man]

I agree with Bass because if anyone thinks they can shoot the 45-70 revolver like this with a 4" barrel, they are nuts! :bigsmyl2:

[44man]

Where would one find the these charts in other calibers, boolit styles, weights? Like in post no.1.
There are none for revolvers or cast boolits in rifles. There are guesses and Greenhill that is for cannons but most is from experience. Seems as if it is not possible to write a formula. One bullet can be tested and a chart made. Easier for the military that uses what they need but hard for cast shooters with thousands of boolits. It would take millions of dollars and several lifetimes! :coffee:
Barrel makers try for a medium so you have overlap. If they made a twist just for one bullet, they would not sell many guns.

[Dan Cash]

I think Mann answered these questions along about 1900, but who reads.

[45 2.1]

Thanks 44Man, I understand.



Mann? How about a first name for petes sake.

Dr. Franklin Mann, author of "The Bullets Flight"....IIRC

[luvtn]

I have a Ruger Redhawk .44 mag, 4 inch barrell ( 1 in 20 twist). I would like to buy a rifle to complement it with commonality of ammo a big consideration. So How come Handi rifles and others have 1 in 38 twist. AARRGG.
luvtn

[44man]

I have a Ruger Redhawk .44 mag, 4 inch barrell ( 1 in 20 twist). I would like to buy a rifle to complement it with commonality of ammo a big consideration. So How come Handi rifles and others have 1 in 38 twist. AARRGG.
luvtn
Take note that the Marlin in .45 Colt and .357 both have 1 in 16" twist rates. Why everyone uses 1 in 38" for the .44 really baffles me.
I think the Greenhill gremlin was let out to run loose! :veryconfu

[9.3X62AL]

I'm not quite ready to shelve and forget Greenhill--I just don't think of it as a "hard and fast" formula. It has merit as a general guideline, and its original velocity envelope is pretty close to that of cast boolits in rifles. Its "constant" of 150 is supposed to be increased to "180" once velocity gets to 2800 FPS, so assuming the 150 constant was predicated on 1800 FPS, the constant could conceivably be increased at a similar rate to the velocity. Not a very constant constant, though.

Some twist rates seem to be almost traditional--one of those "It's how we've always done it" responses. 1-38" in 44 caliber rifles and 1-10 in 9mm handguns comes to mind in this context, both of which are ridiulous extremes in opposite directions.

In fairness, that muzzle pressure question may be one answer to why the 9mm and many 40 S&W barrels continue to be made in 1-10" pitch. I still thnk it is overdone, having seen how WELL both calibers perform using 1-16" twists. But muzzle pressure is the first seemingly valid justification I've read or heard of concerning the matter.

[NSP64]

So, as reloaders we should be able to compensate for shorter barrel/increased muzzle pressure by using faster powders to have lower pressure in shorter barrels at the muzzle. Thus theoretically having the same stable rpm/velocity as a longer barrel.

[44man]

So, as reloaders we should be able to compensate for shorter barrel/increased muzzle pressure by using faster powders to have lower pressure in shorter barrels at the muzzle. Thus theoretically having the same stable rpm/velocity as a longer barrel.
That's a good way to put it!
In a revolver you might need to adjust the alloy to take a quicker pressure rise so the boolit holds shape and doesn't skid.
I am not sure how muzzle pressure changes affect accuracy unless the base is damaged or the crown is bad. There is always muzzle pressure release. If there was none, the gun would not make any noise and everyone knows how loud most guns are.
With a slow powder in a short barrel it just does not all burn, reducing pressure in the barrel only to burn in the air out front. That reduces velocity and the needed spin. Take some pictures at night.
Let's talk about BP for an example. Take one cartridge and barrel length with one granulation, say FFFG. Load with slight compression to max fit and it works fine but keep adding and compressing the powder to get more in. Soon, velocity will start to drop because you keep adding weight to be pushed and the barrel is not long enough to burn it all. Soon you will start shooting plugs of powder out behind the boolit. Some can be cured by having a hole through the powder to expose more to flame, like the fake BP plugs have.
What you have is a limit! Very large revolver calibers with a lot of powder in a short barrel just can't use the powder so a guy needs to speed up the pressure curve with fast powder. Doesn't it sound kind of silly to buy a .500 and cut the barrel down when a much shorter case would work better? Simply put, the larger the case and the more powder it holds, the longer the barrel needs to be.
I have to wonder how much homework MR did with the shorty BFR .44 since it has a 1 in 16" twist? Don't you think they are on to something?
Twist rates and barrel lengths will always be contentious subjects. Some say you can work around it but in the end, it is not true. The wrong twist people might try 500 boolits and every powder, spend years fooling around only to get a few good groups with ONE combination.
I want to pick any boolit, any weight, any length and in one range session have that boolit shoot sub MOA at 100 yards and maintain accuracy to as far as I want to shoot.
I wish more fellas would get serious about twist! :kidding:

[Bad Water Bill]

Since the name of this site is CAST BOOLITS I have one question. Has anyone ever come up with a chart to determine when a cast will turn into vapor due to over spin?

[Dan Cash]

Thanks 44Man, I understand.



Mann? How about a first name for petes sake.

What 45 2.1 said. It is worth a read.

[felix]

Since the name of this site is CAST BOOLITS I have one question. Has anyone ever come up with a chart to determine when a cast will turn into vapor due to over spin?

No. Shot too fast makes the soft boolit not track the lands. Shot too fast makes the hard boolit hit sideways because of erratic muzzle pressure. In other words, it is too difficult to make a non-coated boolit go into the vaporization state. ... felix

[hiram]

No mention of velocity

http://www.montanabulletworks.com/page11.html

[44man]

No mention of velocity

http://www.montanabulletworks.com/page11.html
Just more Greenhill. If you can get that heavy of a .457" boolit stable with that twist I will eat your hat.

[9.3X62AL]

That's quite a site, Hiram. Thanks for posting the link.

Perusing the twist rate charts kinda confirms in my mind that Greenhill is a good guideline, but a poor guarantee.

[firefly1957]

Yes Dr. Franklin Weston Mann "THE BULLET'S FLIGHT"I read the book from cover to cover terribly boring I do not know how he did it suspect it drove him over the edge. The information is very good it is just all the data is a bit over whelming.

[44man]

The problem with Greenhill is that input figures need to be changed and if you fool with it enough you can make anything fit. Go far enough and you will say a 3" long boolit can shoot from a 1 in 1" twist!
When a formula needs changed for every boolit, caliber and velocity, explain what good it is! Fool with input enough and it will match what you are shooting.
Like a computer, stupid in equals stupid out.
Just about every other formula suffers from this. The only way to find what works is testing.
I have read a few hundred published twist charts in my life and in every case they were 100% wrong from what actual experience dictated.
Dr. Mann did a lot of work and understood more then we ever will but I don't think he ever came up with a foolproof formula because I don't think it can be done to cover everything.
Work out what a 173 gr 30-06 bullet of a certain configuration needs, then change the bullet and you need to change input. A dog chasing it's tail!

[44man]

Earlier on in this topic was a reference to rifling land depth. Are deeper lands easier to get better accuracy results from?
From my limited experience lands that are .025" deep suck. Lands that are .040" to .050" have given me better accuracy. Barrels from 1860's through the 1950's had deeper rifling lands/grooves.. and I have found it easy to get good accuracy out of them.
No, that is wrong, lands are bore diameter but can vary in width. Grooves are deeper and can vary in depth. The Marlins are stuck with .003" depth and that is OK with micro groove since there are more lands and grooves but the Ballard should have been about .006" deep.
Muzzle loaders should be about .010" deep.
There is no such thing as land depth.

[Dannix]

Dutch4122 has a target I shot with his 1894 44 Mag that is the equal or better than the one you just posted (5 shots at 50 yards). Load was a cast approximately 300 gr. boolit of my design at close to max. velocity shot over the iron sights that came with the gun. The target was witnessed by BABore and Dutch4122 along with a non forum member. I believe it was his hog load.
Could you share what mould and alloy? I would appreciate it.

[Dutch4122]

The boolit is a group buy C434-265-RF with three crimp grooves. It is basically a standard lube groove version of the Ranch Dog tumble lube C432-265-RF. The alloy was straight wheelweight. It weighs 280 grns out of my w/w alloy.

Hope this helps,

[turbo1889]

I guess I’ll weigh in on this. For starters there is indeed far more involved in boolit or bullet stability then just the length of the boolit as some have been claiming. This is clearly evidenced by the fact that the classic Greenhill formula has had at least two correction factors added to it that I know of one of which was suggested by Mr. Greenhill himself:

http://farm6.static.flickr.com/5297/5527782040_f62a923395_z.jpg (http://www.flickr.com/photos/54455625@N04/5527782040/)

Clearly if the boolit is a solid copper boolit instead of a solid lead boolit this does effect boolit stability as well as velocity both of which have solid backing in the hard sciences.

Personally, I have found that the Greenhill formula with the velocity correction factor works pretty well for my use. Namely, determining the velocity range that I need to push cast boolits in rifles with the twist they already have to get me at least close to a good load. This has helped me to avoid load problems I’ve had before with under stabilizing long heavy weight rifle boolits because I wasn’t pushing them fast enough to give them enough RPM to stabilize them and problems I’ve had with over stabilizing short light weight boolits by trying to push them too fast.

There is a free download ballistic program on this web-site:

http://www.stickledown.co.uk

which is suppose to calculate tables from your inputes that basically give you the same kind of information about a particular boolits stability patterns as the graph the OP contains only in a table format instead of a graph but it uses your inputs from measurements you take of your bullet. Unfortunately, I can’t seem to make it work on my computer (Win-7 x64) even when I try to run it in Windows-95 compatibility mode.

Maybe someone more computer savvy then I am can figure it out and post how to make it run on the newer computer systems since from the screenshots listed showing the program (WinGyro) in action it appears it would be ideal for addressing twist questions like this.

[Dannix]

Thanks Dutch. I appreciate it.

http://castboolits.gunloads.com/imagehosting/thum_111534d81e34d38251.jpg (http://castboolits.gunloads.com/vbimghost.php?do=displayimg&imgid=234)
Thanks for adding this and your comments to the thread Turbo.

Regarding the software you linked to, maybe it will run under WINE, but if you have an old COA of Windows 98 or some such, you could try setting up a virtual machine via VirtualBox. Actually, a VM of ReactOS may do the trick. I need an excuse to tinker with both WINE and ReactOS again, so this may be the app to do it with.

[Olevern]

Not to hijack this thread, but over in cast boolits sub forum is a thread where I could use some help from the vast storehouse of knowledge weighing in here on twist rate for a project I am starting.

http://castboolits.gunloads.com/showthread.php?t=109404