RPM in a nutshell......

[NSP64]

I have tried to read the RPM debate thread and my mind shuts down:( Could anyone break it down into plain english what the RPM threshhold is??? I mean I think it talks about RPM of boolits and the range they should be shot in to give the best chance for accuracy?

[runfiverun]

the whole thing was about the best accuracy occuring at or below the rpm's for certain twist rates.
example a 10 twist bbl has a potential velocity ceiling of 1950 [about]
a 12 twist of 2100 [example]
a 14 twist of 2250 [ example also]

and lets not start this again guys...
some say the best ACCURACY happens at or below these velocities.
others say it is hogwash..
it don't matter what the twist rate is, you just gotta be able to put a package together that works at the higher velocities.
don't matter if it is only for 4 shots.

[Bass Ackward]

Very simply.

The RPM theory basically says that "best" accuracy will be established at the first velocity level that rotation is adequate to stabilize that slug and that accuracy will deteriorate from that point on. It supports the old cast bullet adage to use the slowest twist rate that you can to stabilize any projectile. And there is clearly a basis in fact for this theory.

It's the conclusions drawn by both sides and the numbers established that cause the argument that you read.

[crabo]

How do you determine that it has "stabilized"?

[BABore]

How do you determine that it has "stabilized"?

The boolit's wittle butt precisely follows behind its nose at the maximum range you intend to shoot it.:-D

[blackthorn]

At the risk of throwing gas on the fire----I have tried to follow those threads relating to the RPM "threshold" and it appears to me that the (sometimes) heated arguments revolving around the testing (that is STILL in progress) boils down to trying to determine whether it is possible to achieve equal (or better) accuracy above the certain velocity range that seems to be attainable by most shooters. In MY opinion the dispute is unlikely to ever get resolved to the satisfaction of everyone of us because there are just too many variables that form part(s) of the answer! At the end of the day, what is important is not the end of the journey but rather the thought stimulation, ideas and knowledge found along the way. Having said that, it also appears to me that those threads sort of got hung up on a dispute over "BEST" Vs "ACCEPTABLE" accuracy (likely an over-simplification on my part). Again likely an unwinnable argument given the variables involved coupled with the needs, wants and individual goals of each shooter. For myself, I will continue to read, consider and learn. Have a great day!!

[crabo]

The boolit's wittle butt precisely follows behind its nose at the maximum range you intend to shoot it.:-D

And you determine when that has happened by..... doing what?

[45 2.1]

And you determine when that has happened by..... doing what?

Nice round holes grouped very tightly on a target are a very good indicater. :mrgreen:

[BABore]

Nice round holes grouped very tightly on a target are a very good indicater. :mrgreen:

Yep, uh huh, that's how I'd tell. :bigsmyl2:

[Marlin Junky]

I lost interest in those threads long before the last page but that doesn't mean the topic is not interesting to me. During the testing, I didn't see an effort to isolate the damage to the boolit from the rifling, versus the effect of imparting high RPM to the boolit during flight. I mentioned high speed photography at the muzzle and that fell on deaf ears. Did anyone make an attempt to "catch" the boolits at long range in water to inspect the difference in rifling marks on the boolits... under a microscope? I realize this isn't CSI Miami, or whatever crime show is popular these days; however, it sounds like nobody here really has the resources to prove this theory one way or the other. Am I wrong in assuming this? The thing that keeps me leaning toward believing the RPM theory as stated here (I think it goes something like this: flaws in the casting [boolit] produce larger groups at high RPM) is bunk has to do with the fact that putting a hard jacket around the Pb core results in immunity (to a point) from RPM. Did anyone test this theory with swagged bullets... that should eliminate the "casting void" variable to a certain extent. Maybe all my questions were answered :-? in the volumes of rhetoric that were placed here, I just don't have time to sift through it.

MJ

[NSP64]

O.K. but what is the equation and the rpm max??

[Shiloh]

the whole thing was about the best accuracy occuring at or below the rpm's for certain twist rates.
example a 10 twist bbl has a potential velocity ceiling of 1950 [about]
a 12 twist of 2100 [example]
a 14 twist of 2250 [ example also]

and lets not start this again guys...
some say the best ACCURACY happens at or below these velocities.
others say it is hogwash..
it don't matter what the twist rate is, you just gotta be able to put a package together that works at the higher velocities.
don't matter if it is only for 4 shots.


I get better accuracy from the Krag and '03 at the lower velocities. I thought 1625 to 1650 was the cats pajamas. I lowered to around an estimated(haven't clocked 'em yet) 1550-1575. This has cut down on flyers and tightens thing up. Both barrels are 1:10 twist. Off-hand shooting is quite mild.

Shiloh :castmine:

[onceabull]

If we can keep this thread going,perhaps "Tiger" will entertain us once again ! :twisted: Onceabull"

[sundog]

Try this. Find a powder that seems to work well for a particular load. Without changing the lot of boolits in use, run from a start load on up until groups shrink and then start to open up. Back off to the 'best group' load and that is your threshold for that load and gun combination. At that point, shoot that load a lot in all kinds of environmental conditions and note the changes, especially ambient air temperature extremes which can affect pressure, which affects velocity, which affects rpm.

I dropped out of that conversation long before it was over, because I don't care if it's pressure or velocity or rpm or whether one in an indicator of another. It just doesn't make any difference to me. If it does to someone, then have at it. If someone doesn't like the way I do it, so be it.

[NSP64]

I was just trying to come up with a way to figure best velocity for given boolit weight. Say X boolit shoots good @ 1500fps . If i use a boolit liter than X do i add velocity to make it shoot good?

[45 2.1]

Try this. Find a powder that seems to work well for a particular load. Without changing the lot of boolits in use, run from a start load on up until groups shrink and then start to open up. Back off to the 'best group' load and that is your threshold for that load and gun combination.

Corky makes an excellent point. With some powders and cartridges, you can run through three cycles like this before you hit maximum for the powder. The cycle starts with a vertically stringing group which will tighten up as charge goes up to a bughole group, then starts stringing horizontally as the charge increases, then the cycle will repeat itself. All through the wonder of barrel harmonics. These seem to repeat at about 300 fps cycles in the shotgun speed powders. Try for a 1500fps load and see what happens.

[runfiverun]

try with slower powders also.
i have a load with h-4831 in my 7mau, that is abysimally boring at 50 yds,
and just falls apart at 100 yds due to not enough velocity. but comes around again
and will shoot to 300 yds well enough to hit bowling pins.
one of the points discussed in the thread also, was what effect twist had on forward
velocity, and whether velocity or rpm's fell out in long range shooting.
[ the lineal target test.]

[Marlin Junky]

runfiverun,

That's pretty amazing. How about some load details? What size groups does it shoot at 100 yards? Do you own/have access to more than one 7x57?

MJ

[runfiverun]

i had 3 but sold one to build another so i will have three again.
i started at 36 grains of 4831 and a rifle primer, using the time tested W.A.G. method
and had predicted about 1900 fps [ended up with 1685] so much for predictions.
it did leave some unburned powder in the bbl but shot very well at 50 yds.
when i ran it too 100 the groups were just awful.
but by taking it up to 38gr they started pulling back together again.

the funny thing about my wifes rifle is that it shoots jacketed and cast to about the same
accuracy level at 100 but the 50 yd load in cast is far more accurate.
what i have found in her rifle is that the powder doesn't make a big difference,as long as
you keep the velocities the same it don't care what powder you use to do it with.
2400,4895,4831,rl-19,h-322,aa-2230, whatever.
........but consistent ignition did make a difference in the group sizes.......
i have her h/v load right now at 46 gr rl-19 in win+p 257 bob brass
the same stuff at 51 gr gives her 2775mv in jacketed.

[Marlin Junky]

i had 3 but sold one to build another so i will have three again.
i started at 36 grains of 4831 and a rifle primer, using the time tested W.A.G. method
and had predicted about 1900 fps [ended up with 1685] so much for predictions.
it did leave some unburned powder in the bbl but shot very well at 50 yds.
when i ran it too 100 the groups were just awful.
but by taking it up to 38gr they started pulling back together again.


What load shot awful at 100 yards but was able to hit bowling pins at 300? Do all the rifles have the same twist?

MJ

[leftiye]

Youse guys should go look at this thread. It answers the question about how rpms affect accuracy. If you keep your eyes open that is.

[runfiverun]

M.J. no one was a 10 twist the other was a 9 1/2 twist.
the 9 1/2 twist is the wifes rifle, i was shooting the rcbs 145 silh weighing 146grs
and 19.5 gr 2400 and a win pistol primer. [ yes my 44 mag and 45 colt load]
that is the weird part as there is no way it was overstabilized, and had to settle down.

and leftiye is right [ he probably thought i would never say that.......lol]
about cutting to the quick on the velocity thread.

[Tiger]

If we can keep this thread going,perhaps "Tiger" will entertain us once again ! :twisted: Onceabull"


Hallo,

I am sorry about my absence. I was away in my holidays. I took a good amount of it all at once. This was not the way I want make my appearance when I come back, but seems Onceabull main purpose on this forum is to harass members. I feel that way. This is not like Americans I meet in Germany. I also waiting for Larry Gibson to post more on this rpm adventure. Contrary to some members thoughts I like and enjoy Larry.

Ralf

[BABore]

Hey Ralf, glad to have you back. Some of us really missed you.

You Euro-types sure get lots of vacation time. Time to sit back and enjoy a few hefe weizen's while summer's still here. Another month and it's Oktoberfest time.

[leftiye]

I second BaBore's comment. I too wondered where you were. Good to hear from you again Ralf! Don't worry about Ounce a bull, "it don't mean nothin" as we used to say in the Nam.

[runfiverun]

once a bull was having a litle fun there
good to see you back, tiger.

[Larry Gibson]

The following are from anoher thread and may provide some answers to the question "RPM in a nutshell". As you read them keep in mind that there isnot "RPM limit" as such or a hard and fast RPM number. It is cartridge/bullet deendant. Keep in mind that the adverse affects of RPM (actually the centrifugal force applied by increased RPM) applies to al bullets; cast PP'd and jacketed. It is why even jacketed bullets are made as uniform as possible, why for accuracy we try to kep loads as concentric and uniform as possible. This is to induce as little imbalances to the bullet as possible for the centrifugal force to adversely affect.

Larry Gibson






Not wanting to waste your time but the RPM threshold, if that's what you refer to, is not a limit. It is a threshold, as the name implies, that may be pushed or crossed and even may be lowered. For regular cast bullets (the current popular designs with bore riding noses) in CF rifles using the common reloading methods the RPM threshold is most often between 120,000 and 145,000 RPM.

The "leeway" is dependent on the consistency of ignition, acceleration rate, (burning rate of the powder), quality of the cast bullet, alloy used (ductile yet strong enough to resist set back, sloughing or uneven obturation), fit of the bullet to the throat/leade, square ness of the base of the bullet on barrel exit and of course the concentricity of the bullet (center of gravity rotating around the center of form).

All of the "leeway" is what occurs during the internal ballistic phase when the bullet is still within the barrel and on exit; the less deformation of the bullet during acceleration the better the balance of the bullet. Given a square base and a good barrel crown the launch should induce minimal if any yaw. Thus the well balance bullet is less affected by the centrifugal force applied by the RPM during flight (the external ballistic phase). We must understand that no fired bullets, not even jacketed bullets, are perfect on launch: this why rifles shoot groups instead of the bullets all going into one hole. However, the better balanced the bullet is during flight the more accurate it will be.

The RPM threshold may be lowered simply by producing an unbalance bullet or one with an uneven base on launch.

The RPM threshold may be pushed by using a bullet that fits the throat/leade and is minimally unbalanced during acceleration and launch. This bullet will have minimal yaw and he center of gravity will rotate around the center of form as close as possible. Such a bullets flight is then less affected by the centrifugal forces of the RPM. With such we can increase RPM (i.e. increase velocity within a given twist barrel) until we induce imbalances in the bullet or the already induced imbalances allow the increased centrifugal force (increasing RPM increases the centrifugal force) to cause some amount of inaccuracy (it may be a small or large amount depending on th degree of imbalance and the amount of centrifugal force).

Let's take a typical .30 cal bullet for example; the 311291 shot in a 10" twist 30-06. Cast of an alloy of 16 - 18 BHN (Lyman's #2) we can drive it with the slower pistol powders up to 1700 or so fps and get the best accuracy. If we try to shot it faster with that powder accuracy will start to fall off. (Now someone, please don't post that you shoot it at 1750 fps with 2400 with great accuracy. This is an example and there are variables as I've mentioned). Thus with that load the RPM threshold is around 1700 fps or so.

We can switch to a medium powder like 4895 thereby reducing acceleration and lessoning the deformation of the bullet until we get into the 1900 fps range. The accuracy level between the 2 loads is the same but by using different loading methods we have increased the RPM threshold of the 4895 load.

We can then switch to a slower powder like 4350 or 4831 and up the same level of accuracy to 2100 fps or so. Thus, gain, we do so by lowering the acceleration rate and lessoning the adverse imbalances until a higher velocity/RPM rate has been achieved.

How do we know when we exceed the RPM threshold for our specific load? Simple; accuracy deteriorates. It will deteriorate faster with faster acceleration. At some point it will really go bad. If pushing the RPM threshold and you are testing at 100 yards you should also shoot at 200 yards if you think you've a god load. Taking the above 30-06 for example; if we get best accuracy at 1900 fps of say 1.5 moa for 5 shots with a 4895 load and we push the velocity to 2100 fps for hunting load. At 100 yards our accuracy for 5 shots is 2.5 moa. Is that a good load for hunting out to 200 yards? Maybe yes and maybe no; if we shoot a 5 shot group at 200 yards we would expect the group to open in a linear fashion giving a 5 - 6" group. That may or may not be acceptable hunting accuracy but that is not the point. If the RPM threshold is exceeded the 200 yard group size will not be linear in nature from the 100 yard group size. If the 200 yard group size is 6+" or larger then we have exceeded the RPM threshold. The size of the non linear group at 200 yards tells us if we are exceeding the RPM threshold and whether by a lot or a little.

Thus we see, the RPM threshold is not a “limit” as many seem to erroneously believe.

Larry Gibson

Quote:
Originally Posted by Pat I.
Larry I'd pretty much agree with this but from my experience and studies I'd apply it to 30 calibers only. I've found that smaller calibers raise the threshold and larger calibers lower it. I've gotten my best accuracy out of an 8 twist 6.5 at 1750 fps which translates to 157,000 RPM.
That's a generally held assumption and there is much to support it. Given an equal defect (in equal % to bullet weight) or imbalance in the cast bullet the farther away from the center of spin the greater the adverse affect on accuracy seems to be. It is compounded by the distance the center of spin is away from the center of gravity. The smaller the bullet the less these distances are. That's why larger diamter bullets seem to be more affected. However, the twist rate for most larger diameter bullets is slower so it appears the RPM threshold is less. I've not come to a specific conclusion on either yet.

The fact is the RPM threshold is just that; a threshold. It is not a specific limit as many here still want to erroneously believe. The specific point where the RPM threshold is for a specific cartidge and load is dependent on several things as I mentioned. Regardless of what some may want to think; when we push a cast bullet to a certain point of velocity the centrifugal force of the RPM will overcome the stability of the bullet to some degree and some amount of inaccuracy will result. The faster we push the velocity the the higher the RPM and the greater the inaccuracy will become as the centrifugal force is increased via the increased RPM.

Larry Gibson


Quote:
Originally Posted by felix
It's not the RPM, but the surface linear speed. ... felix
Correct; the larger the diameter of the bullet (given and equal RPM and equal defect or imbalance) the higher the surface speed of the bullet. This is why the defect has a greater affect from the centrifugal force. Also if the defect is on the out side of the bullet the adverse affect will be greater than if the defect is inside the bullet (air bubble for instance) and closer to the center of spin and center of gravity.

Larry Gibson

[StarMetal]

The following are from anoher thread and may provide some answers to the question "RPM in a nutshell". As you read them keep in mind that there isnot "RPM limit" as such or a hard and fast RPM number. It is cartridge/bullet deendant. Keep in mind that the adverse affects of RPM (actually the centrifugal force applied by increased RPM) applies to al bullets; cast PP'd and jacketed. It is why even jacketed bullets are made as uniform as possible, why for accuracy we try to kep loads as concentric and uniform as possible. This is to induce as little imbalances to the bullet as possible for the centrifugal force to adversely affect.

Larry Gibson






Not wanting to waste your time but the RPM threshold, if that's what you refer to, is not a limit. It is a threshold, as the name implies, that may be pushed or crossed and even may be lowered. For regular cast bullets (the current popular designs with bore riding noses) in CF rifles using the common reloading methods the RPM threshold is most often between 120,000 and 145,000 RPM.

The "leeway" is dependent on the consistency of ignition, acceleration rate, (burning rate of the powder), quality of the cast bullet, alloy used (ductile yet strong enough to resist set back, sloughing or uneven obturation), fit of the bullet to the throat/leade, square ness of the base of the bullet on barrel exit and of course the concentricity of the bullet (center of gravity rotating around the center of form).

All of the "leeway" is what occurs during the internal ballistic phase when the bullet is still within the barrel and on exit; the less deformation of the bullet during acceleration the better the balance of the bullet. Given a square base and a good barrel crown the launch should induce minimal if any yaw. Thus the well balance bullet is less affected by the centrifugal force applied by the RPM during flight (the external ballistic phase). We must understand that no fired bullets, not even jacketed bullets, are perfect on launch: this why rifles shoot groups instead of the bullets all going into one hole. However, the better balanced the bullet is during flight the more accurate it will be.

The RPM threshold may be lowered simply by producing an unbalance bullet or one with an uneven base on launch.

The RPM threshold may be pushed by using a bullet that fits the throat/leade and is minimally unbalanced during acceleration and launch. This bullet will have minimal yaw and he center of gravity will rotate around the center of form as close as possible. Such a bullets flight is then less affected by the centrifugal forces of the RPM. With such we can increase RPM (i.e. increase velocity within a given twist barrel) until we induce imbalances in the bullet or the already induced imbalances allow the increased centrifugal force (increasing RPM increases the centrifugal force) to cause some amount of inaccuracy (it may be a small or large amount depending on th degree of imbalance and the amount of centrifugal force).

Let's take a typical .30 cal bullet for example; the 311291 shot in a 10" twist 30-06. Cast of an alloy of 16 - 18 BHN (Lyman's #2) we can drive it with the slower pistol powders up to 1700 or so fps and get the best accuracy. If we try to shot it faster with that powder accuracy will start to fall off. (Now someone, please don't post that you shoot it at 1750 fps with 2400 with great accuracy. This is an example and there are variables as I've mentioned). Thus with that load the RPM threshold is around 1700 fps or so.

We can switch to a medium powder like 4895 thereby reducing acceleration and lessoning the deformation of the bullet until we get into the 1900 fps range. The accuracy level between the 2 loads is the same but by using different loading methods we have increased the RPM threshold of the 4895 load.

We can then switch to a slower powder like 4350 or 4831 and up the same level of accuracy to 2100 fps or so. Thus, gain, we do so by lowering the acceleration rate and lessoning the adverse imbalances until a higher velocity/RPM rate has been achieved.

How do we know when we exceed the RPM threshold for our specific load? Simple; accuracy deteriorates. It will deteriorate faster with faster acceleration. At some point it will really go bad. If pushing the RPM threshold and you are testing at 100 yards you should also shoot at 200 yards if you think you've a god load. Taking the above 30-06 for example; if we get best accuracy at 1900 fps of say 1.5 moa for 5 shots with a 4895 load and we push the velocity to 2100 fps for hunting load. At 100 yards our accuracy for 5 shots is 2.5 moa. Is that a good load for hunting out to 200 yards? Maybe yes and maybe no; if we shoot a 5 shot group at 200 yards we would expect the group to open in a linear fashion giving a 5 - 6" group. That may or may not be acceptable hunting accuracy but that is not the point. If the RPM threshold is exceeded the 200 yard group size will not be linear in nature from the 100 yard group size. If the 200 yard group size is 6+" or larger then we have exceeded the RPM threshold. The size of the non linear group at 200 yards tells us if we are exceeding the RPM threshold and whether by a lot or a little.

Thus we see, the RPM threshold is not a “limit” as many seem to erroneously believe.

Larry Gibson

Quote:
Originally Posted by Pat I.
Larry I'd pretty much agree with this but from my experience and studies I'd apply it to 30 calibers only. I've found that smaller calibers raise the threshold and larger calibers lower it. I've gotten my best accuracy out of an 8 twist 6.5 at 1750 fps which translates to 157,000 RPM.
That's a generally held assumption and there is much to support it. Given an equal defect (in equal % to bullet weight) or imbalance in the cast bullet the farther away from the center of spin the greater the adverse affect on accuracy seems to be. It is compounded by the distance the center of spin is away from the center of gravity. The smaller the bullet the less these distances are. That's why larger diamter bullets seem to be more affected. However, the twist rate for most larger diameter bullets is slower so it appears the RPM threshold is less. I've not come to a specific conclusion on either yet.

The fact is the RPM threshold is just that; a threshold. It is not a specific limit as many here still want to erroneously believe. The specific point where the RPM threshold is for a specific cartidge and load is dependent on several things as I mentioned. Regardless of what some may want to think; when we push a cast bullet to a certain point of velocity the centrifugal force of the RPM will overcome the stability of the bullet to some degree and some amount of inaccuracy will result. The faster we push the velocity the the higher the RPM and the greater the inaccuracy will become as the centrifugal force is increased via the increased RPM.

Larry Gibson


Quote:
Originally Posted by felix
It's not the RPM, but the surface linear speed. ... felix
Correct; the larger the diameter of the bullet (given and equal RPM and equal defect or imbalance) the higher the surface speed of the bullet. This is why the defect has a greater affect from the centrifugal force. Also if the defect is on the out side of the bullet the adverse affect will be greater than if the defect is inside the bullet (air bubble for instance) and closer to the center of spin and center of gravity.

Larry Gibson


Global Warming :takinWiz:

[runfiverun]

joe:
now we all know there are ways to pass this up.
protect the base of the boolit, push long time, etc..
but your average boolit from lyman/rcbs whomever, has it's limits and this is as easy as any of them to pinpoint an accuracy zone.
for general work and ease of use, the threshold works.
especially when just getting started.

[StarMetal]

joe:
now we all know there are ways to pass this up.
protect the base of the boolit, push long time, etc..
but your average boolit from lyman/rcbs whomever, has it's limits and this is as easy as any of them to pinpoint an accuracy zone.
for general work and ease of use, the threshold works.
especially when just getting started.

....many here don't know how to even get close to that limit. Run...I pushed the group buy Kurtz to 2879 fps in the Swede one day and the boolit still stayed on the target paper, in fact there was a group, it didn't fly off the entire target backer like Mr Gibson's in one of his 6.5 tests. That's 265753.8 rpm. Now you tell me where the limit is for that bullet and that 50/50 AC alloy?

[pdawg_shooter]

I paper patch, witch supports the bullet in the barrel and limits deformation from acceleration. However, using pure lead (2% tin added) I have found the limit to accuracy is around 2200fps/2250fps. This is true in a 25-06 1 in 10, 3 different 30cals 1 in 10, 375 H&H 1 in 12, and 2 different 45cals 1 is a 1 in 14 and 1 is a 1 in 22. However with a bhn of 18/18.5 I have taken a 30 cal, 1 in 10 to just over 3000fps with MOA accuracy.

[Pat I.]

There's 13,810 members on this forum. Every time RPM or the 6.5 topic comes up it's the same 5 or 6 guys that jump in and argue. I'd really like to hear from some of the 13,804 or 5 others out there who might have played the HV or 6.5 game. Guys come in and out of these discussions saying they're going to have a go at it and never get heard from again. If you tried it and it worked out tell everyone exactly what you did and provide the results. If you tried it and it shot like **** tell everyone exactly what you did and provide the results. Otherwise it's like a dog chasing it's tail because everyone already knows what the 5 or 6 usual suspects think.

[Larry Gibson]

....many here don't know how to even get close to that limit. Run...I pushed the group buy Kurtz to 2879 fps in the Swede one day and the boolit still stayed on the target paper, in fact there was a group, it didn't fly off the entire target backer like Mr Gibson's in one of his 6.5 tests. That's 265753.8 rpm. Now you tell me where the limit is for that bullet and that 50/50 AC alloy?

Starmetal

You really have a hard time understanding the RPM threshold and how it affects accuracy as evidenced by your posts regarding this from day one. I'll attempt to explain it to you one more time. A load that has a velocity above the RPM threshold does not mean the bullets have to be totally unstable and fly off target. The bullets may in fact, and most often are in fact, still rtoating around the axis of the bullet. However, there is yaw and the center of rotation is not close to the center of form. The centrifugal force of the increased RPM is causing the unbalanced bullet to fly in a larger and non linear (as the distance increases) spiral around the line of trajectory.

Your example of that the bullets "still stayed on the target paper" (8x11.5 as you've posted) doesn't mean they were not adversely affected by RPM. If that "group" you think was there was larger than the 1/2" "bughole" groups you get at much lower velocity and RPM then you exceeded the RPM threshold for that bullet. It is very plain for everyone to see, except you, that you did in fact exceed the RPM threshold. Understand?

BTW, just to set the record straight; the example you have now mentioned twice where I had bullets go off the target was one using your and 45 2.1s technique. It was also wth 45 2.1s choice of powder (3100) and using his method of selecting the load. The facts is the starting load was around 2 moa or less and the groups got progressively worse as the velocity and RPM were increased until the bullets no longer held target. That, starmetal, is a very good example of how exceeding the RPM threshold adversely affects accuracy. You exceeded the RPM threshold with your load and I exceeded the RPM threshold with my load. The fact that one load stayed on target is not relvent, both exceeded the RPM threshold. That is not a good example to use if your intent is to show you did not exceed the RPM threshold with that load.

Larry Gibson

[StarMetal]

Starmetal

You really have a hard time understanding the RPM threshold and how it affects accuracy as evidenced by your posts regarding this from day one. I'll attempt to explain it to you one more time. A load that has a velocity above the RPM threshold does not mean the bullets have to be totally unstable and fly off target. The bullets may in fact, and most often are in fact, still rtoating around the axis of the bullet. However, there is yaw and the center of rotation is not close to the center of form. The centrifugal force of the increased RPM is causing the unbalanced bullet to fly in a larger and non linear (as the distance increases) spiral around the line of trajectory.

Your example of that the bullets "still stayed on the target paper" (8x11.5 as you've posted) doesn't mean they were not adversely affected by RPM. If that "group" you think was there was larger than the 1/2" "bughole" groups you get at much lower velocity and RPM then you exceeded the RPM threshold for that bullet. It is very plain for everyone to see, except you, that you did in fact exceed the RPM threshold. Understand?

BTW, just to set the record straight; the example you have now mentioned twice where I had bullets go off the target was one using your and 45 2.1s technique. It was also wth 45 2.1s choice of powder (3100) and using his method of selecting the load. The facts is the starting load was around 2 moa or less and the groups got progressively worse as the velocity and RPM were increased until the bullets no longer held target. That, starmetal, is a very good example of how exceeding the RPM threshold adversely affects accuracy. You exceeded the RPM threshold with your load and I exceeded the RPM threshold with my load. The fact that one load stayed on target is not relvent, both exceeded the RPM threshold. That is not a good example to use if your intent is to show you did not exceed the RPM threshold with that load.

Larry Gibson

You're all bull pucky Larry. You didn't exceed anything except your capability. You haven't reached the velocity I have with the Swede. In fact I'm tired of listening to your pucky. It's your wrong loading techniques making your bullets goes screwy. You know darn well our Swedes have the same twist.

Global Warming!!!! :takinWiz:

[NSP64]

There's 13,810 members on this forum. Every time RPM or the 6.5 topic comes up it's the same 5 or 6 guys that jump in and argue. I'd really like to hear from some of the 13,804 or 5 others out there who might have played the HV or 6.5 game. Guys come in and out of these discussions saying they're going to have a go at it and never get heard from again. If you tried it and it worked out tell everyone exactly what you did and provide the results. If you tried it and it shot like **** tell everyone exactly what you did and provide the results. Otherwise it's like a dog chasing it's tail because everyone already knows what the 5 or 6 usual suspects think.

I usually read the first few threads till the fighting starts then move on to a different thread. This (my) thread is 1.5 yrs old. I started a different thread asking about Min RPM for accuracy and opened the same can of worms. If say a .223 at 1500 fps in a 1-8 twist is min for accuracy (no keyhols). I was fishing for anyones experiences.

[StarMetal]

I usually read the first few threads till the fighting starts then move on to a different thread. This (my) thread is 1.5 yrs old. I started a different thread asking about Min RPM for accuracy and opened the same can of worms. If say a .223 at 1500 fps in a 1-8 twist is min for accuracy (no keyhols). I was fishing for anyones experiences.


It's Mr. Gibson comes along with his rpm threshold pucky. I know the answer he will give to my next statement and will bet 100 rounds of loaded 6.5 Swede Kurtz loads he's been wanting. Here goes: I've done extensive shooting of my Colt HBAR AR 15 with cast. I've had cast up to full power jacketed loads. Remember now that this is a 7 twist. I deliberately tried to get the NEI 70 grain bullet to either explode or fly off the entire target backer. Mine you now my target backer is some five foot square. Now here's the part where I bet the ammo. I put a sheet of printer paper up with a black dot in the center for just an aiming reference. Got that Larry, just an aiming reference. Not your asinine accusation that it was for a target group. Not a one of the bullets that I fired went off that printer paper. The velocity was in the 31-3200 fps range. That's 329142.8 for the 3200 fsp and 318857.1 for 3100 fps. Not only didn't the bullets explode or strip, they stayed on the paper. Because this so badly destroyed Gibson's theory he till this day claims it as my target group test, not rpm. This is with 50/50 alloy water quenched.

Now I think your question about the velocity you want to shoot is very reasonable. I've gotten suitable accuracy in that range clean up into the 2000 to 2500 fps range with both that 70 grain bullet and NEI's 55 grain Loverin. I was using such powders for the full loads as 4350 and 3100. I've even shot test loads with 860 and 5010 suplus!! Yeah, those are beyond slow for the 223, but you know what, they worked....and not they didn't foul up any part of the AR 15 gas system "except" unburned kernels left in the chamber did leave dents in the next fired rounds.

Not only is the velocity and rpm of these test surprising to me, even more surprising it that the rifling groove in an AR 15 Colt are very very shallow. So that amazed me that alloy didn't strip. I'll say one thing about the chroned bore and chamber....wish all my rifles had it....so darn nice to clean. Never was there any leading in the barrel. There wasn't even the nasty grey wash on the flash hider. The very slow powders didn't use fillers, the faster ones did.

[Pat I.]

I didn't realize this thread was that old. I can't help you with your question because I have no idea if there's a minimum velocity for a twist. I suppose the only way to find out is by trial and error. Should be easy enough to figure out because if the bullets are going in sideways they're going too slow. :-)

The only thing I can't really figure out about the people who are so against the fact that barrels are twist limited when it comes to velocity is their unwillingness to prove it shoulder to shoulder on the line.

I guess that and why people are in such a hurry to be big shots that they don't bother to read or don't understand the question.

[Larry Gibson]

I usually read the first few threads till the fighting starts then move on to a different thread. This (my) thread is 1.5 yrs old. I started a different thread asking about Min RPM for accuracy and opened the same can of worms. If say a .223 at 1500 fps in a 1-8 twist is min for accuracy (no keyhols). I was fishing for anyones experiences.

Lots of loads available from numerous sources; here's some of mine.

I've killed alot of ground squirrels with a 225415 over 4 gr of Bullseye in my 9" twist bolt gun. Velocity is 1525 fs and accuracy holds moa If I do a good scruteny and eliminate visually defective cast bullets. I size .225 and lube with Javelina. GCs are Hornady's and no filler/wad is used. The same load shoots well out of my 7" twist Bushmaster AR but I've not chronographed it. It does not function the action. As to minimum RPM I have run Lyman's 225462 cast of dead soft lead as low as 500 fps with excellent accuracy at 50 yards. This was with Bullseye also. With 2.2 gr of Bullseye under Lymans 225428 cast dead soft runs at 1050 fps and shoots 3/4" at 50 yards for a very good .22LR equivelent load in the 9" twist Savage Competition rifle. I also shoot that same load as a grouse load in my Savage 24V but it has a 14" twist. I've also shot lots of Beeman's Crow Magnum .22 cal pellets over 1 gr of Bullesye for a light gallery and pest removal load.

Larry Gibson

[NSP64]

Thanks Larry that is exactly what I was looking for.:drinks: