Mine always had rifling marks on them. Not as defined as a standard GG boolit, but definitely visible.Originally Posted by 45 2.1
However, I use green bar paper, and I have the boolits sized to the exact size that the paper would crush them if they were any bigger, so the patch bumps the groove into the underlying boolit fairly easily.
Perhaps paper is more accurate than steel?
Precision in the wrong place is only a placebo.
With many things it is a matter of degree. Hit yourself in the head with a six ounce hammer and then repeat with a three pound hammer. The depth of rifling marks on a bullet is markedly different between a paper patched and regular cast bullets.
Disclaimer: The above is not holy writ. It is just my opinion based on my experience and knowledge. Your mileage may vary.
OK, that hurt, and I don't feel any wiser. LOL!
I would have thought that the paper would have merely cushioned the boolit's transition from the case neck to the throat and lead of the rifling, allowing it to get there without being damaged by the misalignment of the two. I assumed that the paper acted like a shock absorber so that the boolit could "get religion" in the barrel with less damage.
However, I could be way off. I do believe this is the crux of the issue, but it's just a theory of mine. Someday, I'll have the equipment in place to really get a better idea of what happens to that boolit as it leaves the barrel. Until then, I'm just trying to find a possible solution that makes sense of all the evidence.
Last edited by MBTcustom; 11-10-2013 at 10:14 PM.
Precision in the wrong place is only a placebo.
Goodsteel
The RPM theory holds that a cast boolit will no longer be able to keep itself together past about 140,000rpms (forgive me if that is wrong) because the alloy tries to sling itself apart in mid air which creates a compounding problem that deteriorates accuracy very quickly. (ie, once that boolit gets a little janky from the forces of inertia, it's all over but the cryin)
That is wrong. At no time have I ever said the RPM threshold caused bullets to come apart. There is a reason that some bullets will spin apart from too much RPM but that has nothing to do with the adverse affect on accuracy that exceeding the RPM threshold has. The RPM threshold also does not cause bullets to become unbalanced and lose their stability. The RPM threshold is when the unbalanced bullets centrifugal force is such that it causes the bullet to depart from it's line of departure/line of flight and go off on a tangent or go into a slow helical arc which radii increases non-linearly as the range increases around the line of flight. The bullet is most often still stable and flying point forward when the RPM threshold is exceeded.
You are correct about the unbalanced or damaged bullet being the problem. However, it is those unbalances and damage that the RPM act on while the bullet is in flight. The more unbalanced/damage and/or the higher the RPM the greater the inaccuracy will be. At some point of RPM the bullet will go off on the tangent or the slow helical arc.......that point is the RPM threshold. With regular cast bullets it is most often in the 120,000 - 140,000 RPM. With PP'd bullets (because they are less damaged/unbalanced) the RPM threshold is somewhat higher and with jacketed it is most always higher to the point of exceeding the velocity capability of the cartridge/rifle.
Larry Gibson
I understand that, and I agree completely.
So, if it were possible to get the boolit started down the barrel undamaged, then it would probably emerge undamaged and have the same RPM potential that the paper patched boolit is capable of, right?
So the limiting factor is not the cast lead boolit, nor the RPM, but rather the reloader and the precision that he holds his loads to, and how well he assembles them and manipulates the components he has to get that boolit to work with the rifle instead of getting beat up by it, right?
Precision in the wrong place is only a placebo.
goodsteel
So, if it were possible to get the boolit started down the barrel undamaged, then it would probably emerge undamaged and have the same RPM potential that the paper patched boolit is capable of, right?
That is correct. However, understand that you can get a perfectly concentric and balanced cast bullet (very difficult to come up with) started down the barrel undamaged but it can be heavily damaged during acceleration. It's why we must balance out the case capacity with a slow burning powder keeping the time/pressure curve as slow and low as possible to push the RPM threshold up.
So the limiting factor is not the cast lead boolit, nor the RPM, but rather the reloader and the precision that he holds his loads to, and how well he assembles them and manipulates the components he has to get that boolit to work with the rifle instead of getting beat up by it, right?
Yup, there in lays the "limit". As I've always said; the RPM threshold can be moved up or down depending on how well the bullets are cast of a correct alloy, the components used, and the skill with which they are assembled for the specific firearm. And if we do all correct and can push the RPM threshold high enough then we could run into the cast bullet exceeding the elastic/plastic capability of the alloy and potentially come apart.....but that's another story........
Larry Gibson
Sounds reasonable!
I'm going to find a way to get you out here for a steak dinner one way or another!
I'm going to bust that RPM threshold, and then I'm going to take you out to my favorite shootin place. If that happens, bring a long range rifle. It's the closest thing to a wind tunnel you can get and still be outside.
Precision in the wrong place is only a placebo.
I swore I would never get in the middle of this topic, but here it goes. Now I am not a wordsmith so I am just going to throw some things out to think about. How a person chooses to look at them will determine where they fall on this topic.
How fast can a cast boolit be spun and retain accuracy? Has that point ever been determined? I offer the following link as food for thought. Pay attention to posts #2 	 before coming to any conclusions.
(link didn't work. cut and pasted in next post)
The next comment is in reference to post #43. A jacketed boolit came apart when shot out of a fast twist barrel. The question is "why"? Was it:
a - the rmp threshold was reached for that bullet?
or
b - the rifling in the barrel compromised the integrity of the jacket allowing it to come apart under high rpm's.
If the answer is b then I have to point out that the CAUSE was NOT high rpm's. The cause was a compromised jacket. Kinda tips my hand, huh? If that very same bullet was placed in an accelerator sabot(assuming it was .22 cal) would it still come apart in a 1:10 twist '06? my bet is no.
I have been following these threads for the last couple of years and have read the threads from before that. There are those that say that rpm is the cause and those that say it is not. There is one common theme that all agree on if one takes the time to read what is actually written, and has been repeated on this thread. Goodsteel hit it on the head, Char-gar pointed it out, and Felix and, yes, even Larry.
The condition of the boolit after it leaves the barrel is THE determing factor as to the degree of accuracy at a given rpm. The first to effect this is the alloy and the last is the crown of the barrel. In between is a whole bunch of stuff like casting, sizing(did it go through the sizer straight?), seating in the case, chamber(is it straight?), fit in the throat (that is KING after all) and barrel condition just to name a few. As Larry pointed out in his last post rpm acts upon the imbalance in a boolit. This imbalance is THE CAUSE and the degree to which it is imbalanced determines where the rpm threshold is for a GIVEN boolit, chambering, load and rifle. That is why it is a threshold and not a limit.
When all the arguing and discussions are dissected it all comes down to one thing, is rpm THE CAUSE? All the other specifics most are in agreement with.
Do I think rpm is THE CAUSE? No, I think the relationship between rpm/twist rate/accuracy that Larry's data clearly shows is an indicator of everything that came before it. It can be a symptom of a problem in the loading/shooting sequence or it can be an indicator that you did something right.
For the record I would only state that I believe Larry's data in this field is good data. My experience and what others have posted only serves to back it up. I believe his methodology is good as it can be repeated and has been. I just disagree with his conclusion, as has been stated many times, that rpm is THE CAUSE. It is a major factor just not THE CAUSE. It's influence is determined by all that came before.
I also think that ultimately it comes down to terminology, semantics and a major case of which came first, the chicken or the egg. We know why rpm effects accuracy. I just think too much emphasis is placed on it. Work with what you got and control what you can control. If you have a 1:10" twist '06, well, deal with it.
Darrell - the preceding was my opinion and only that. If you disagree my feelings are not hurt.
oh yea, Nobade, if I was to build a cast boolit shooter it would be exactly like yours, twist rate included. Why fight a 1:10" twist when a 1:14" twist is much easier on the boolits?
Last edited by brotherdarrell; 11-10-2013 at 11:44 PM.
"It's better to keep your mouth shut and appear the fool than to open it and remove all doubt"
Eph. 2:8-10
Kill da wabbitt!!! KILL DA WABBITT!!!!
My link did'nt work so I cut and pasted. Posts are by Bullshop in reference to cast and accelerators.
Post #2
Bullshop
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We have been messing with it some. Have done 30/30, 308 and 06, mostly 06. You will have to size the boolits to .224" but it has little to do with pressure. The problem with larger diameter is they do not consistantly release from the boolit. When running over size boolits we find the sabots anywear from just in fron of the bench to all the way through the target. When running .224" boolits all the sabots are about 30' in front of the bench. You dont need that seater tool if you have a lube sizer. All you need is a .308" die and a top punch that fits the boolit.
We are using a 55gn CBE boolit sized .224" without lube or gas check. We got a top velocity from the 06 of 4300 fps but about 3 moa. At 4000 fps we get about 1 moa.
Forget about the load data that comes with the sabots. All I can say is that it is safe, but I think they dont know people have chronographs now. To get the accuracy and velocity it takes powders considerably faster than anything you would use in those cartridges with normal weight bullets.
We started with the load data provided and worked each powder to the limit and ran out of room before we got real speed. We just kept going to a slightly faster powder and do the same thing each time until we finally got to the right burn rate that would give the velocity with normal pressure and good load dencity.
We are casting from straight WW but we are quenching for these kind of speeds. We have taken some small game with them and they do just what you would think a 55gn boolit would do at 4000 fps MV.
Hope that help ya a bit.
Blessings
BIC/BS
post #9
Here is some stuff I found,
4/28/07 45F
30/06
case - FC
bullet - 53gn CBE qww @ .224"
primer - WLR
powder - 52.5gn H4198
OAL - 2.896"
AMV - 3968 fps
ES - 16
test group @ 100 yards 5 shots @ - 1.046"
I have some recorded velocities for other powders but this was our bets load.
10/14/04 33F
30/30
case - RP
bullet - 22 Bator 6/1 WW/Monotype @ .224"
primer - CCI#250 LRM
powder - 38.2gn Scott 4197 (AA#2015)
no velocity listed
noted that this load shot to the same POI as 170gn 24gn 4197
12/5/06 20F
case - RP
bullet - 63gn RCBS
primer - RP#2 1/2
powder - 30.5gn H 4227
noted as good load, MAX
For seating depth it seemed more important to have the petals of the sabot about half covered by case neck than any relationship between sabot and rifling. Seating longer so the petals had no support had a negative affect on accuracy even though the sabot may in this way be in contact with the rifling the way you would expect with a boolit.
Some of these little details were important to good consistant accuracy.
With the 30/06 load listed we were getting better accuracy than from Rem factory sabot ammo at the same average velocity fired from the same rifle.
The load gave good average accuracy from three differant 30/06 rifles we tried it in.
Have fun and be careful. All the usual warnings do apply.
Blessings
BIC/BS
"It's better to keep your mouth shut and appear the fool than to open it and remove all doubt"
Eph. 2:8-10
Kill da wabbitt!!! KILL DA WABBITT!!!!
The rpm threshold seems to explain all the theories being put forth here the best. If there truly is no wall or threshold then why can't i shoot a 200 grain boolit in my whelen with 1/14" twist at 2900 fps with 1/2 min of angle @ 100 yards like i can regularly with hornady 200 grain jacketed?( I'm asking this seriously - trying to learn) After a lot of trial and error, the best i can come up with so far is just under or just over min. of angle anytime i get near or at 2400-2500fps. At about 2600 the best i've done so far is 2 1/2 groups and the same load may shoot 4" the next group. Also each different alloy from straight lead to heattreated ww will go increasingly faster with accuracy.
It does seem to be an rpm in relation to hardness which is affecting balance or something type of thing. Anyway i keep hitting a wall or threshold or whatever, that i can't seem to pass. All the alloys and loading tricks i've tried so far fall into Mr. Larry's theory but i'm new to cast in rifles so if there's a
way around the wall , i'd like to know what it is....Not arguing with anyone...just looking for answers. OK, just saw the above posts, must have come in while i was typing this out....that explains some of it.
Last edited by 35 shooter; 11-11-2013 at 12:13 AM.
Well, just for the record, this is all just science and fun as far as I'm concerned. There really is no reason to get anywhere over 2000fps IIHO as long as you are deer hunting etc.
No reason in the world you need that much destruction and mayhem to be inflicted on your groceries! (see the link in my sig line).
I need a load that will kill deer like a champ, and I get that at 1800fps no problemo. However, the experimenter in me likes to know how fast, how long, how deep, how strong etc etc etc. Just like some people like to trick out a car to go faster than they would ever drive to work, I'm that way with boolits. Don't ask me why it's so deliciously invigorating! I don't have a clue! It's just something that I think about and enjoy (perhaps a little too much).
Precision in the wrong place is only a placebo.
I saw those pic's when i joined up....awesome. That's the very reason i'm going in the morning with 1800fps. This will be my first season with cast in a rifle. I've done it before with a 44 pistol tho @ about 1100 fps. Put the smackdown on em for sure. Like you i like to experiment and the only way i know to learn is ask questions. This first year with the rifle has sure been a learning curve just working up loads...problem is i'm thinking that curve is just getting started good. Got a long way to go to catch up with you guys. Like i said..not arguing with anyone....learning!
LOL! We're all just experts in training! You may think you have a long way to go, but you probably know more than me in one or two areas.
Remember: The most important questions you can ask are who, what, when where, why, and to what extent. Ask what do I see, but more importantly what don't I see. You're rifle is the best schoolmaster of all, and it never suffers from misinformation. It is always right, and will give you the answers you are after if you know how to learn from it.
Most folks (Often, myself included) listen to the boom sounds, and look at the holes, but that's all they manage to observe in the process of shooting.
I used to go out and just blast away buckets of WW metal and didn't learn a darn thing for it. These days, every shot is a plume of information that must be gathered and tried to be understood. There are many mysteries, but you have to pick something and tinker with it till you understand it, then pick something else. Divide and conquer.
Keep it up! The RPM debate has spurred many a booliteer to look closer, and try to understand what is happening.
It's kind of like a "if a tree falls in the woods and no one sees it" kind of a riddle in some ways. Kind of like the theory that "a perfect piece of glass is one of the strongest substances on earth" because glass must have a flaw to begin a crack, and theoretically, a perfect piece of glass will have no way to begin a crack, so it should be amazingly strong. Only problem is, there is no perfect piece of glass that can prove the theory! LOL!
Precision in the wrong place is only a placebo.
True dat!
Disclaimer: The above is not holy writ. It is just my opinion based on my experience and knowledge. Your mileage may vary.
brotherdarrell
This imbalance is THE CAUSE and the degree to which it is imbalanced determines where the rpm threshold is for a GIVEN boolit, chambering, load and rifle. That is why it is a threshold and not a limit.
That is basically it. However if there is no imbalance there is no threshold. Imbalance is still not the root cause nor is RPM. The root cause is the centrifugal force. If there were no centrifugal force even the imbalanced bullet would shoot accurately and the bullet with the damaged jacket would not spin apart regardless of the how high the RPM was.
Also keep in mind that centrifugal force has it's effect on the bullets accuracy only in the exterior phase of ballistics (flight). Thus the only way to keep the centrifugal force low and reduce it's adverse effect on accuracy is to reduce the RPM through lower velocity or a slower twist with a given velocity.
All the quality machining, blueprinting, casting of perfect bullets and excellent benchrest loading techniques can do absolutely nothing to affect centrifugal force. They only affect how much imbalance is in the bullet on exit from the barrel. The centrifugal force from whatever level of RPM is present then has an adverse effect on the imbalances, if any, of that bullet causing some level of inaccuracy.
Even before the RPM threshold is reached all bullets are adversely effected accuracy wise from centrifugal force. The effect of centrifugal force on any imbalance causes the bullets center of spin not to coincide with the center of mass or with the center of form. It's why guns shoot groups, even those of the highest accuracy potential from machine rests. There is a good explanation of this in Hornady's Manual with pictures even.
Larry Gibson
What interest me is to see if the 1:14" twist rate will keep a bullet like 200 grain Lyman #311299 stable out to five or six hundred yards.
I don't know about that Larry. Just from what I have seen in my short legged experience leads me to believe that most factory rifles have very specific problems built into them as safety measures, and as inconsequential defects. These things make it nearly impossible to get a concentric boolit past the crown of the rifle. These things are also very fixable, if you know how.
Now, how much effect does the correction of these defects have on the boolit and the RPM limit of them? I'm still figuring that out, but I'm hoping it's dramatic.
For instance, do you think it's really RPM that's getting you, or the damage that naturally happens when you slam a soft boolit into fast twist rifling?
Why is it that a powder with a gentler energy profile seems to give better accuracy from cast boolits?
Could it be that it allows the boolit to get started engraving better before it really gets the kick in the pants?
Could it be that the very fact that faster twist rifling has a more aggressive engraving characteristics is the real reason the RPM appears to be a limiter?
Have we just been hammering nails into trees?
Last edited by MBTcustom; 11-11-2013 at 02:39 PM.
Precision in the wrong place is only a placebo.
Tim, what you have said is indeed correct. All of it. The RPM rule is just a composite method of advance REPORTING of the projectile's problem, not the problem itself. Damage done to the projectile is due to the act of acceleration, or externally by the forces within the projectile afterwards. ... felix
Last edited by felix; 11-11-2013 at 02:59 PM.
felix
So, what we all need is smooth bore guns and stabilizers on the projectile like the M1 tank. That will solve all our problems, no?
I have pretty well convinced myself that how fast you accelerate the bullets will have a big impact on it's accuracy. That is why accuracy starts to go south with fast powders like 2400 when you get past 1.8K fps or so. The alloy will make a difference.
Contrast that will very slow powders like WC872 that push the bullet out of the barrel with less damage due to slow progressive acceleration. Fine accuracy can be had at higher than that obtainable with 2400 or like powders. Again, the alloy will make a difference.
I think the RPM thing has something going for it. But it is just one of the factors that limit accuracy at higher velocities. Very few things in life are "either or", most are "both and".
1. RPMs imparted
2. Temper of the metal
3. Depth of rifling engraving on bullet
4. Speed of powder
5. Design of the bullet
6. Probably a bunch of other factors as well.
Disclaimer: The above is not holy writ. It is just my opinion based on my experience and knowledge. Your mileage may vary.
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