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Thread: Ideal twist rates for cast boolits vs. jacketed. Different? Why?

  1. #81
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    Quote Originally Posted by Love Life View Post
    Amazing!! Good thing I get to ignore neck tension, diameter, etc and just sit some bullets over 'splody powder and shoot sub-moa to 1,000 yards.

    I apologize for the snarkyness, but brass prep and all that jazz is just as important in shooting jacketed. What I don't have to deal with in jacketed is sub par, off balance, projectiles...that may or may not act like accordions.
    The methods are not only different, but ten thousand times more important with cast than jacketed. You have to go to full-on benchrest loading tolerances and attention to vibration, pressure curve, just to equal the accuracy and velocity of factory loaded jacketed ammo with cast boolits.

    Yes, Larry, you understood me correctly. The problem is, like Rick alluded to, it hasn't been explained in a straightforward, conversational way. Even then, the full understanding doesn't come until one actually ACHIEVES a good launch with components he manipulated and assembled himself, usually after a lot of false-starts and errors. I'm not saying I have a "full understanding", I don't, but I've gotten the high-velocity launch really close to right in six rifles now and a lot of the same principles apply. Bob described most of it when he posted about making a chamber cast and mimicking it closely with the entire loaded cartridge. Then there's alloy, pressure curve, and the little tricks that matter a lot, but that really IS a subject for another thread, and I think I have sidetracked the twist subject of this thread enough.

    Gear

  2. #82
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    "Was this due to imperfections in my cast bullets that I didn't know about or was it due to an "RPM/Barrel Twist" thing that was eluded to by the OP? If your bullets ARE cast concentrically, loaded concentrically and flying concentrically, it's hard for me to wrap my head around "RPM" or "Barrel Twist" as being the problem."

    You may have a problem getting your head around it but that's ok. However you also realize you are seeing the end result of "something" that is causing; "I have two 30 caliber rifles. One is a 10-twist and the other is a 10.6 twist. I've shot both of them at just a tad over 2000 fps before and neither one would group worth a darn at a hundred yards. Neither did either one leave leading in the bore or oblong holes in my target." Assuming you are casting, loading and lining everything up concentrically then obviously there is another "game" afoot. The laws of physics and ballistics are there and are known. Thus as butch2570 puts it; "Anything that I can think of that rotates on a fixed center or axis that has a slight unbalance to one side is made worse by increasing the Rpms". We can cast, load and do all the concentric alignment we want but there still is the problem (unbalancing of the bullet) that the acceleration can and does do to the bullet before it clears the muzzle (launch). After that it is what the centrifugal force of the RPMs do to the bullet in flight that remains the question.

    However, This thread is supposed to be about twist rate for "ideal" stabilization of the bullet. We can mitigate the adverse affects of the centrifugal force on the bullets imbalances by using a barrel twist that is just fast enough to fully stabilize the bullet. Doing that provides better accuracy, especially with cast bullets. The secondary benefit in seeking the "ideal" twist for a cast bullet is that many times we are then able to keep the RPM Threshold above or very close to the maximum obtainable velocity for a cast bullet in the cartridge used. That then negates the RPM threshold almost completely and we need not then concern ourselves with that.

    However, in the case of your '06 you have the 10" twist barrel and knowing about the RPM threshold can then allow some movement of it upward if that's desirable. Using a better designed cast bullet that fits, an appropriate alloy, a slower burning powder with close to 100% load density and some other somewhat anal loading techniques you could push the RPM threshold upwards so 2200 - 2400 fps with useable accuracy is possible. It's not easy but it can be done.

    Larry Gibson

  3. #83
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    Quote Originally Posted by Love Life View Post
    Amazing!! Good thing I get to ignore neck tension, diameter, etc and just sit some bullets over 'splody powder and shoot sub-moa to 1,000 yards.

    I apologize for the snarkyness, but brass prep and all that jazz is just as important in shooting jacketed. What I don't have to deal with in jacketed is sub par, off balance, projectiles...that may or may not act like accordions.
    I think if you read a little more of the last couple posts you'll get a bit better understanding. A lot of the techniques of loading cast bullets to HV are the same as with jacketed bullets. We do have to be quite anal about some things just as geargnasher mentions. Much of the difference comes from understanding what is going to happen to accuracy (bad) with cast bullets if you don't pay attention to other details that you don't have to with jacketed bullets. That's because you pay a lot of $s these days for quality jacketed bullets where the manufacturer has paid attention to those details for you. Also you must understand the force of acceleration and what it does to a cast bullet vs a jacketed bullet. Just because we put a perfectly cast bullet into a perfectly prepped case in perfect concentricity to the bore doesn't mean we get a perfect bullet out the end of the muzzle. Jacketed bullets can be awfully forgiving in that regard but cast bullets are not, especially when we push them hard and fast.

    Part of the intent of this thread is to discuss what we can do to mitigate that by using an "ideal" twist for cast bullets instead of the general "all purpose twists" most often found for use with jacketed bullets. BTW; a lot of very good cast bullet shooting can easily be and is done in the standard jacketed bullet twist barrels. When kept to reasonable velocities even cast bullets can be pretty forgiving in accuracy with minimal loading technique. Even some pretty poor cast bullets can give quite good yeomen accuracy out to 100 yards w/o much trouble in loading at all. Just depends on what you want.

    Larry Gibson

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    Quote Originally Posted by Larry Gibson View Post
    However, in the case of your '06 you have the 10" twist barrel and knowing about the RPM threshold can then allow some movement of it upward if that's desirable. Using a better designed cast bullet that fits, an appropriate alloy, a slower burning powder with close to 100% load density and some other somewhat anal loading techniques you could push the RPM threshold upwards so 2200 - 2400 fps with useable accuracy is possible. It's not easy but it can be done.

    Larry Gibson
    Wait a minute.

    When I mentioned that I got near 2400 fps out of a ten-twist, with "useable accuracy" (1.25 MOA for multiple, ten-shot groups at a hundred yards on different days is pretty usable), you demanded, rather rudely, to see it done in person. The implication was obvious, I think.

    Now you're telling others how to do it. I can show how I did it, but I'd like to see you go first here. Please give some details, pics of groups and load details, including what tolerances or anything else specifically that you changed to "push up" the threshold compared to what you could do with your normal loading routine that limited-out at the top of the threshold. This is the sort of stuff a lot of people are interested in right now and following hoping to learn. Maybe you could start a new thread, titled "How to get good groups past the RPM threshold" or something.

    Also, I'm getting a distinct vibe that you are starting to assimilate the term "pushing the rpm threshold up" with stretching the twist rate out and loading to higher velocity. I DON'T THINK SO. That would be called "lowering the RPM and increasing velocity to stay within the threshold". The threshold remains the same for the equivalent loading techniques the way I read your theory.

    Gear

  5. #85
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    Now I have a better understanding. Thank you.

  6. #86
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    You have to go to full-on benchrest loading tolerances and attention to vibration, pressure curve, just to equal the accuracy and velocity of factory loaded jacketed ammo with cast boolits.
    Why is that Ian?

    Because we have a more fragile projectile we must load it in a manner that protects it.
    Why is that Brad?

    our cast bullet will easily flow into those spaces and that leads to unbalance even if we started with a perfect bullet
    Why is that a bad thing?

    If the RPM theory is totally wrong then none of those things shuold matter?
    Why is it that when you perform the most basic ladder test to find the nodes, everything goes to pot rather suddenly?
    I know it has nothing to do with RPM, because that cant be the right answer (Dont ask me why it can't be the right answer, it just cant OK?) but surely if the centrifugal force applied to the imperfections that you left or imparted to the boolit while loading and shooting it is not to blame, then what could possibly be the reason?

    The way I look at it (and I could be totally wrong on this) is that the "RPM threshold" or whatever you want to call it is a schoolmaster. It exposes your errors and to a point, the limit of the very projectiles we are shooting.
    Think of it like MPH on a stock car. Sure the driver can do a lot to work with what he's got, and eek out the most competitive edge by being darn handy with a clutch, but he's not a car builder, hes a car driver.
    We wear both hats. We make the boolits and we also load and shoot them, but a janky boolit will only go so fast until its limits are breeched, just like a stock car can only go so fast till you hit top end on the MPH.
    In order to win a race, you need to build the car and drive it better than anybody else, but when we are talking exclusively about RPM, it's like we are talking exclusively about MPH.
    If you go to the dealership and buy ten brand new Dodge Chargers, take them home and rip out the governors. Then take them to the track and run em up till they top out, you might come to the conclusion that "A Dodge Charger can only go 120-140 MPH" just like Larry says that a cast boolit can only go 120,000-140,000 RPM typically.
    Well, up walks a master mechanic and tells you your full of it! a Dodge Charger can do 200 all day long if you do X,Y,Z.
    Next guy walks up and calls BS and says that he can get that thar Charger up to 230mph if you give him a week.
    The thing is, there is still a limit to a certain process. Sure you can fudge it up or down, and sometimes you get lucky, but for the most part there is a number that nobody wants to tackle.
    Precision in the wrong place is only a placebo.

  7. #87
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    If I could step in here for just a second?
    I just read what Larry wrote in this thread along with what each of you fellers put down, as well as the links that Larry put up.
    Just reading it, with no history to help me read anything else into it, I see the threshold described as the place where accuracy suddenly goes to pot. This can be found with any cast boolit load by doing a simple ladder test.
    Also, I see him saying that the FPS (thus the RPM) where this phenomenon occurs is higher with a better fitting, better balanced boolit.
    That's what he says.
    That also appears to be what everybody is saying, and other than this strange aversion to the three letters "RPM" being used in a post, the difference comes down to loading techniques and groups, both of which are being refused on a matter of principle.

    I think two things need to happen.
    First, you fellers can apologize to eachother for the years of berating posts back and forth, and believe me, there's enough blame to go around on both sides.
    Next, I suggest that Ian has the best idea yet. Start a thread and work together to hammer out a consensus on this issue. I guarantee you could all get where you are going ten times faster if you were working together.
    Precision in the wrong place is only a placebo.

  8. #88
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    Quote Originally Posted by btroj View Post
    Ok, possibly true Tim but look at the closed sticky I linked to.

    It says accuracy will begin to detonate between 120,000 and 140,000 rpm. A 2400 fps load in a 10 twist barrel is over 170,000 RPM.

    Not an insignificant difference. If 170,000 is possible then what does the 120,000 to 140,000 threshold mean?

    That is over a 20 percent difference, not insignificant at all.
    That's true Brad, but I just ran into a wall with my 1909 Argentine reamed to 30-06 (that's another way to get a killer tight-necked 06 BTW) and when I dropped down to 1500 FPS I went from a shotgun blast to MOA.
    Every rifle is different. This one has a rotten bore, and Ian's has a superb bore. Which will damage the boolit worse?

    BTW, ironically, it was Ian that told me to try a tame charge of Unique. LOL!
    Precision in the wrong place is only a placebo.

  9. #89
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    +1. Way too much great info to get into a war here. I'm trying to soak this all up and not ready for the well to go dry on this subject.

  10. #90
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    Quote Originally Posted by btroj View Post
    Looking at this another way it means I should be able to achieve the same RPM level in my 12 twist barrel so that gives me 2800 fps at 168,000 rpm.

    2800 fps with that case and a 180 gr bullet exceeds the limits of what can be done with that case most likely. Problem solved, my twist rate is fine.
    Certainly! If you use these top end dies, top end brass, and top end boolits, and feed them in an absolutely top end rifle, you should be able to get it up to 2800, but there is no way I could do that with the Argentine without a lot of fancy footwork, and I can tell you without hesitation that most milsurps would be just as difficult (not impossible, but difficult, especially for the average booliteer).
    To the average booliteer, all he wants is to know how fast he can push without spending a fortune and jumping through flaming hoops of fire to get there, and in that case, the easy answer is to just go by the RPM theory and call it a day. In most cases, there is no reason why your shouldn't be able to get 120,000 RPM with standard, hulk smash, reloading techniques.

    That said, I'm still waiting to see anything even close to this with any of my rifles. Certain people say it's possible, so I'm just taking their word for it.
    Last edited by MBTcustom; 09-22-2014 at 10:47 AM.
    Precision in the wrong place is only a placebo.

  11. #91
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    Of course, some of us are wanting to take it to the next level, and "push up the RPM threshold" as Larry puts it.
    We have the tools, the means, and the dicipline to make it happen, and all that is required is to pick a rifle and git-er-done. However, without guidance or collaboration, that will be a rough trial and error way to reinvent the wheel.
    I would like everyone on this sight to have both.
    Right now they have neither.
    All that is required is a hand shake, a buried hatchet, and some honest give and take between peers.
    Precision in the wrong place is only a placebo.

  12. #92
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    Quote Originally Posted by btroj View Post
    I think I can safely say that many of us want collaboration. What we don't want is interference or naysaying.

    The thread I want to see is all about the particulars of making better ammo, how to cast better bullets, how to size and lube them without damaging them, how to fit them, and the case, the chamber/throat, and how load differences change the ability to get good accuracy.

    If we can stay on topic and keep the nastiness away then it can work. What we need to keep at bay is summed up in a single word- EGO.

    What we need are open minds. Minds that don't predetermine things to not be possible. Minds that are willing to accept things at face value. Minds that are willing to speak of what is being done NOW, not what was done in the past.

    I want a thread of doers, not thinkers. People who are actively involved in the process as it happens. People who are willing to get their hands dirty and DO the work.

    I know of at least one other person who feels the same way.
    Absolutely. So remember those fine words from my favorite book: A soft answer turns away wrath.
    This can happen Brad. It can be under way in less than a week, but it takes a commitment on your part, on Ians part, and on Larry's part that no matter what, there will be no slandering, nor trolling till an answer has been arrived at.
    I'm asking for just one thread where the three of you agree to work together towards the goal you are all going for. No matter what anybody says or writes.
    I'm asking you to sail to the Newfoundland, and burn the ships till you have built something instead of tearing each other down all the time and undermining each other.
    I would ask for your word on that, and I will moderate.
    This is not a trick, nor a snide jab at anyone. I am asking you politely, for cooperation with a couple friends of mine.
    Last edited by MBTcustom; 04-20-2014 at 10:47 PM.
    Precision in the wrong place is only a placebo.

  13. #93
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    A thread that only the 3 people who own the "special" rifles can input or help collaborate? Nobody from any other shooting discipline is allowed to ask questions or possibly chime in?

  14. #94
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    I do happen to have a 308 barrel...

    Let me get the fat lady burnt out again and I'll get the 308 barrel screwed back on.

    However; I feel we have all done a great job of self moderation here and I see no reason why that couldn't happen in another thread.

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    "All that is required is a hand shake, a buried hatchet, and some honest give and take between peers."

  16. #96
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    I can't stop the static, but there is much you can do to squelch it by how you respond Brad. If anybody get's too far out of line, I would be right there to keep the dogs off your back, but the basic commitment between the shooters to keep it solid and not fight is an obstacle only you can control.
    I'll do my part, but you guys have to do your's.
    I'm sure that if you guys are making progress, the general membership will look on in anticipation. If it's a civil thread then people act civilly. If its a MMA free for all, then your gonna have a crummy thread that is short lived.
    Precision in the wrong place is only a placebo.

  17. #97
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    So no laughing at each other and saying "Neener!! Neener!!! Neener!!!!"?

    Things are only fun until they stop being fun. I'll fail with you and much will be learned. People can take the info or leave it.

    I've been grasping at straws all over the forum from just about all the shooting disciplines trying to wrap my mind around this.

    I still want my polygonal rifled barrel...

  18. #98
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    You're rifle is almost complete Brad. I polished the barrel to a high shine yesterday. All the details are coming together. This baby's gonna shoot!
    All that is left is pretty much stock work.
    Precision in the wrong place is only a placebo.

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    I will view this with interest and any PM to delete off topic posts will be done,
    [The Montana Gianni] Front sight and squeeze

  20. #100
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    Quote Originally Posted by MT Gianni View Post
    I will view this with interest and any PM to delete off topic posts will be done,
    Thank you.

    I think that helps.

    I also think an open agreement amongst the major parties needs to be in place. That can be hashed out via PM if required. I have already sent a PM to some regarding this concept.
    You will learn far more at the casting, loading, and shooting bench than you ever will at a computer bench.

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Abbreviations used in Reloading

BP Bronze Point IMR Improved Military Rifle PTD Pointed
BR Bench Rest M Magnum RN Round Nose
BT Boat Tail PL Power-Lokt SP Soft Point
C Compressed Charge PR Primer SPCL Soft Point "Core-Lokt"
HP Hollow Point PSPCL Pointed Soft Point "Core Lokt" C.O.L. Cartridge Overall Length
PSP Pointed Soft Point Spz Spitzer Point SBT Spitzer Boat Tail
LRN Lead Round Nose LWC Lead Wad Cutter LSWC Lead Semi Wad Cutter
GC Gas Check