Thanks a lot for you research, I learn quite a bit and it explains why my 1:8 Blackout shoots so well at 1700 fps and probally will not go much faster with cast.
As others say, I may not re-barrel my 1:8 Blackout Ar to shoot faster light boolits but I will look into better twist rates for my next Rifle.
Originally Posted by Larry Gibson
Are we forgetting the goal/objective is high velocity with the ternary alloynaked cast bullet? Changing a barrel is one of the variables. Especially when building a rifle, rebarreling a rifle or reboring arifle. Many here do just that and many are indeed using slowertwists. Several here have had a 30 XCB recently made for them andhandicapped themselves by not using a 14" or slower twist as Ispecified. They also insist on using bore riding bullet designs with longnoses and short bearing surface. I also specified a 26"+ barrellength which none of the recent 30 XCB builders paid any attention toeither. Then they wonder why they run into the RPM threshold. Yes, alot of us have learned and progressed but some have not.
BTW; I have runinto the RPM threshold with my 14" twist Palma barrel rifle. The RPMthreshold for that rifle sits just above 2640 fps which is just above 135,000RPM. The additional problem at that level is pressure. My accuracyload at just over 2600 fps runs 40,000 psi. At the RPM threshold for thePalma rifle it runs 42,000 psi. It appears some of the bullets begin toplasticize at that psi. That is why I designed the 30x57 some years backnow known as the 30 XCB here. That cartridge should give 2700 -2900+ fps (depending on barrel length) at a lower psi which is pushing the RPMthreshold up.
Now back to the essence of your question; how do I push the RPM Threshold upwith the 10" twist whatever I have rifle? Assuming that's your question(?) and you will; “will change alloy, mould, or powder along with modifyingload technique”?
I have answered this question numerous times in the past but will do soagain.
To push the RPM threshold up use bench rest case preparation on your fireformed cases. I necksize the cases to give .002 - .003 necktension. I Mostly use an appropriate sized Lyman M-die to flarethe case mouth (a .31 for .30 cal cartridges with .310 - .311 sized bullets).
Use a standard level primer such as Federal 210s, WLRs, Rem 9 1/2 or CCI200s.
Use as slow a burning powder that will give 80 - 100% load density withconsistent ignition in the 30 - 40,000 psi range. I mostly use RL19, AA4350,H4831SC and RL22. I weigh powder chargesthat do not throw within .2 +/- gr. Iuse a Lyman 55.
Use a cast bulletof appropriate design that has a bearing surface of 60 - 65% minimum, a shortnose and fits in the cartridge neck with the GC seated at the base of the caseneck and the front drive band just off the leade. I find the Loverindesign is working the best.
Use a hard yetmalleable ternary alloy with the antimony and tin balanced and not over 5% ofeach. I WQ my bullets for a BHN of 24 - 26. Be anal when casting; goslow and smooth to cast quality bullets. Be anal in bulletsort/selection. I do a visual inspection (using a large bench mountedlighted magnifying glass)and reject any bullet not perfect; fill out of anydrive band or the shank, holes, wrinkles or rough cratered sprue cut areall reasons to reject. I reject probably 40 - 50% of the bullets onthis visual inspection. Those are usually pretty good bullets and mostly getshot with accurate loads in other rifles below the RPM threshold. Theyare just not good enough for this purpose. I take the remaining bulletsthat passed the visual inspection and then weight sort them. I usuallyend up with about 50 - 60% of the 311466s within +/- .4 gr of eachother. Those are the bullets I use for HV loads to push the RPM Thresholdwith. The same anal selection process should apply to any otherbullet. The bullets should be as perfect as possible and within +/- .5 ofone % of each other weight wise.
I seat the GCseparately using Hornady GCs, usually with the GC seater in the Lyman 450. I size the bullet as close to "as cast" as possible if it fits thethroat of the chamber. I usually find a cast bullet sized at .0015 -.003 over the groove diameter will shoot the best. The diameter of the throatand the length of throat usually determine the sizing of the bullet as you wantthe bullet to “slip into the throat and the barrel with a very good fit butwith as little resistance from sizing the bullet as possible. I lube all thegroves with a soft lube that will purge from the bullet within 20' of themuzzle.
Work up theloads and use a sufficient sample; sorry but 3 and even 5 shots isn’t it. Yes you’ve a lot of care gone into selectingthe cast bullets to test. You haverejected a lot of them but now is not the time to scrimp on too small a testsample. Use 10 shots preferably. If youcall a shot bad then the remaining 9 “good” shots will still give you gooddata. Use a solid test bench with a goodrest (doesn’t have to be expensive but good is imperative). Use good bench shooting technique. Don’t shoot too fast and keep the barrelcool. Test at 100 yards initially. A shorter range will tell you nothing. Do notignore flyers if they are not a called shot that goes to call. Flyers are telling you something, don’tignore them.
Chronographyour test strings. If you don’t you’reonly guessing at the velocity and RPM. The max effective range of a guess is zero meters. The ES and SD will also provide good measuresof consistent loads.
Maintain goodrecords.
When you thinkyou have a good load then load up 25 test rounds. Shoot 5 shots to foul the barrel; shootslowly so to not heat the barrel up too much. Then shoot a 10 shot group at 100 yards. Let the barrel cool and then shoot a 10 shot group at 200 yards. If the 10 shot 100 yard group is good but the200 yard group is more than twice the size then the load exhibits non linearexpansion and the RPM threshold is exceeded. Be a bit reasonable here as the chance of exactly twice the size isremote. If the 100 yard group is 1.5”for example and the 200 yard group is within say 3 – 4.5” then you have a goodload with probable linear expansion that is not exceeding the RPMThreshold. However if the 200 yard groupwas say 5 – 8” then the load exceeds the RPM Threshold and accuracy as therange increases will get much worse.
Let us considera different perspective; if it’s a hunting load then that 5 – 8” group at 200yards may be entirely acceptable as you never shoot game past 150 yards. Thus, even though the load exceeds the RPMThreshold it still then is a “useable” load, at least in my opinion.
However, ifaccuracy is the name of the game at HV then that load won’t do unless the 200 yardgroup is very close to twice the size of the 100 yard group. If that’s the case then load up 30 morerounds and test again with 10 shot groups at 100, 200 and 300 yards. If the linear dispersion is correct then the200 yard group will be about twice the 100 yard group and the 300 yard groupwill be 3 times the size of the 100 yard group. When that happens you have an excellent load.
Now if you areexpecting jacketed bullet velocity with the same accuracy using cast bullets withyour 10” or faster twist barrel then you might consider adding copper to thealloy and heat treating it, PPing or perhaps PCing.
We have learnedand we have progressed but some of us understand there are some things on ourbeloved cast bullets, especially the plain ternary alloyed naked ones areprobably just not going to do. Thus toachieve our goal of HV with such a cast bullets we do what is necessary toachieve it such as; rebarrel with a slower twist, use a different alloy, use adifferent bullet design, use a different powder and modify our loadingtechniques. We do this to achieve an achievablegoal.
Larry Gibson
Interesting, my barrel should be finishing out at 28 inches or just over. I suppose that was never stated but I'm amazed Tim never shared that info with you. Then again it was clearly stated in post 57 of the XCB thread that you participated in. Here is what I stated on 10/1/13
My barrel is a Palma taper Krieger. One in 12 twist, should finish to 30 inches or so. It will go on a Savage action and be put in a BR type laminate stock. It will be heavy and that is fine with me. It will never see use in the filed, I wanted a pure target type rifle.
Changing to a slower twist doesn't "push" the threshold at all, it reduces the rpm for the same velocity. It gives you more velocity for the same rpm but it doesn't in any way "push" the RPMs.
I am all for changing load techniques, alloys, and moulds. Those are true, viable, variables that everyone here can comprehend and afford. I'm not looking to make change that benefit gunsmiths or barrel manufacturers, I'm looking for changes the average Joe can understand and make.
You will learn far more at the casting, loading, and shooting bench than you ever will at a computer bench.
I understand where you are coming from Larry. You are very well written and you seem to know how to use a camera, notebook, and keyboard nearly as well as a trigger.
The work you have done here is commendable, as most people are perfectly happy running their rifles well within the RPMTH and that is the truth. That is what is reproducible in any rifle, and the rest of this is either cutting edge boolitry, wishful thinking, or wild speculation.
I personally believe there is a place beyond the RPMTH where something very interesting might happen. I base this belief on all the people who say they did it (never mind the fact that for them the keyboard is a much handier piece of electronics than a digital camera or the English language).
I hope to find a load that runs well above the RPMTH someday. It's a tantalizing goal that I just cant shake (any goal worthy of perusing will be elusive after all!) but I have read some of your posts, and I think that rather than a pot at the end of the rainbow, the RPMTH is real, tangible, provable, and consistent.
I have been told that the "secrets" to HV cast lead shooting is posted here for anyone who cares to dig it up, but I have been searching the archives for months and while I find many jabs, sneers, trolls, allusions, carrots, rabbit holes, "groups" in the middle of shotgun blasts, unfinished tests, unexplained results, and "how dare you ask for anything better than this toiletry" comments, I trip over your writings just as often, and they are filled with careful explanations (based on science and documentation) pictures, demonstrations, and references to respected sources.
I may not come to the exact conclusions you have, but if you are looking to gain my respect, this is the way to do it.
I see nothing like this from people who claim anything different/better. I gave my undivided ear and friendship to some of these, and I found nothing but bigotry, ignorance, and an absolute inability to formulate the simplest tutorial, explanation, or logical argument. In fact, they only succeeded in convincing me that you are 100% right as rain. It took a while, but they talked me right out of their point of view.
Now as to the XCB rifles, there are only 4 now in existence.
One for geargnasher (you might not have noticed it because he has posted precious little about it since I delivered it to him)
One for btroj (nearing completion)
One for Lamar (also nearing completion but not finished)
and one for me which is assembled but only 15 shots have been taken with it (hooray! it didn't blow up!)
My rifle was made with a Remington 700 takeoff barrel because that was all I could afford. It's 21.5" long and 1-10 twist. Believe me, I wish I could afford a slow twist Kreiger, but I'm too busy building them for other people for peanuts to be able to drop that money on myself.
I know the twist is wrong, and so is the barrel length, but I'm not trying to prove anything. I just wanted a fun rifle to mess with, and if I learn something in the process, then I'm happy. I am going to be finding the RPMTH with this rifle, and experimenting with low velocity accuracy, but I also want to load it up to the gills and see how bad I can lead it up. LOL! One thing is for sure: Since I am gentleman enough to give every man his own space, and recognize each person for where they are and where they come from, it seems I will be doing this alone without the help of the self proclaimed "experts".
Who knows? maybe I'll find that pot of gold at the end of the rainbow? I can assure you that I will have fun in the process and I will post pictures of groups as well as (gasp) documentation of what I did and how I did it, and exactly how badly it sucked or didn't. One thing is certain though, and I make no bones about it: I will not ignore clearly written science, nor the laws of physics. If I find a place above the RPMTH that accuracy is attainable and reproducible, and I succeed in doing so, it will square with the RPMTH. It could be there are nodes of accuracy and each projectile has two or three RPMTH's? Perhaps the terminology will change, but the science never will.
It's all good.
Precision in the wrong place is only a placebo.
That's great, but what's the twist? Go back and read the thread "we" participated it and see what twist I recommended.
As to what is "pushing the RPM threshold up" I guess your definition of "is" is different than mine. Makes no difference as the goal is the same. Besides I've already explained ad nauseum about pushing the RPM Threshold up according to your definition in my own rifles of "fast" twist. If you doubt that then go have a look at my 6.5 Swede thread. Look at the accuracy I was getting at 2100+ fps which is 197,000+ RPM. Does that meet your criteria? If so then read how I did it and note the description of how above; they are the same technique. I can give you more examples but I'm wasting my breath as I've explained it all to you before. Now soon you'll have a very fine rifle with an excellent 12" twist long barrel in a very good cartridge for the purpose. The normal RPM threshold for the 12" twist will be from about 2000 fps to 2335 fps (120 - 140,000 RPM). To bad you didn't go with a 14" twist. However, do things right and lets see if we can "push" the RPM threshold up with that longer barrel by using a slower powder to lesson the time/pressure curve and with a bullet of proper design. Perhaps you'll learn how it's done?
Speaking of the bullet; what is your intended cast bullet?
Powder?
Larry Gibson
I don't have a single bullet or powder in mind. I will try what I think will work and see what happens. Alloy will be varied as well.
tim, ever think you found what you looked for because you had already decided what you believed?
You will learn far more at the casting, loading, and shooting bench than you ever will at a computer bench.
Absolutely.
I believe in science. I believe in honesty. I believe in being a gentleman. I believe in doing to others as I would have them do to me. I believe in telling the truth (to myself first, and then to everyone else). I believe that doing the right thing toward a complete stranger is more important than bending the truth to preserve a friendship. I believe in moderating evenly no matter who is trying to whisper in my ear.
Yep, I have no place for people who believe otherwise, or troll peoples hard work or a different point of view.
Last edited by MBTcustom; 06-23-2014 at 11:56 PM.
Precision in the wrong place is only a placebo.
By gawd I think we believe in the same things!
Charter Member #148
Larry,
Your 'proportional amount' is talking to you (us).... It may be in a language we don't understand at the moment. But it's a clue to success......
While I understand your goal here; I think your use of the term 'RPM Threshold' is giving too much credit to a variable which has many variables already in its makeup. I certainly am not discrediting all your hard work on this! You are working hard for some repeatable baselines which is good. Please let me throw out some thoughts as this is not my first rodeo.
"RPM".... This term is usually used for the rotational speed of an object that rotates in a stationary position. Our boolit has both rotational speed and linear (forward motion) speed. An engineer can calculate the RPM of a cast iron flywheel and the resulting surface feet per minute to know if said flywheel is safe at that RPM. Our boolit is adifferent story...
Let's take your 14" twist gun for our example. You know the muzzle velocity from your chronograph. So some simple calculations gives us an "RPM". IS THIS A REAL NUMBER?
Put another way..... when your boolit leaves the barrel is it in fact making ONE REVOLUTION IN 14"? How about 100 yards? I've tested a lot on these questions; so let me answer: One revolution in 14"? The boolit can make one revolution in 14" just out of the gun. BUT IT MIGHT NOT AS WELL! At 100 yards? NO! The distance traveled per revolution becomes LESS! It will continue to change and will not be 14" again! I've proven this and so has Mann over one hundred years ago. This is the definition of "going to sleep" by the way.
Bottomline... Being RPM is related to distance in our case with our boolit; it is a variable in its own right and not necessarily accurate or trustworthy.
Let me throw out what may be causing the proportional amount discrepancy you are seeing... I think maybe 'torsional distortion' ... Almost ALWAYS for me when I see a serious accuracy degradation with fast twists at fast speeds; and if I can find or recover a fired boolit; I see WIDER land engravings on the boolit than actual land width! This 'torsional distortion' can really mess with distance traveled per revolution!
Your thoughts on more 'bearing' surface on the boolit is a good one Larry... I agree if HV is the goal. But if we think what is imparting our 'spin' to our boolit, the length is short. Even 5/8" is little to guide one turn in 14" as we leave the muzzle. With a perfect boolit/rifling fit you'll guide the rotation to 1 in 14"... If you wallow out the land travel you might get anything for 1 in ??" 'Torsion distortion' is aggravated as the twist goes faster for any given velocity that initiates it.
I think I would add your same exact test boolits, but sized down and paper patched to the equation... I know you want to achieve a 'bare boolit' application... But this would be a good indicator if 'torsional distortion' was the culprit of your 'proportional amount' changes if they suddenly improved using a boolit with better traction!
Eutectic
Eutectic
Your 'proportional amount' is talking to you (us).... It may be in a language we don't understand at the moment. But it's a clue to success......
I think you are misunderstanding what I meant by "proportional amount(?). The "proportional amount" I refer to is simple a quantification of the difference in accuracy capability between the 3 rifles. Let's say at the best accuracy (intrinsic accuracy) one barrel produces with the best of match jacketed bullets is 1.3 moa accuracy, the 2nd barrel 1.6 moa and the 3rd barrel 1. 75 moa. Then with our cast bullet load the 1st barrel gives 1.95 moa, the 2nd barrel 2.4 moa and the third barrel gives 2.6 moa. We can say the accuracy is consistent because each load is about 1.5% of the intrinsic accuracy with each barrel when it is compared to it's own intrinsic accuracy. However, if the same load then produces 3.1 moa in the 1.3 moa barrel and 2.6 moa in the 1.75 moa barrel we know something is afoot as the "proportional amount" is now askew at 1.5% to 2.4% difference. Basically "proportional amount" is comparing the accuracy difference of each barrel to itself before we compare it between the barrels.
While I understand your goal here; I think your use of the term 'RPM Threshold' is giving too much credit to a variable which has many variables already in its makeup. I certainly am not discrediting all your hard work on this! You are working hard for some repeatable baselines which is good. Please let me throw out some thoughts as this is not my first rodeo.
The title simply is a title. The RPM creates centrifugal force which is the real culprit. There are a lot of variables which is why the RPM threshold is not a hard and fast figure or "limit" as some want to think. The RPM Threshold is that point generally between 120- 140,000 RPM where, because of the many variables, that accuracy will begin to degrade.
"RPM".... This term is usually used for the rotational speed of an object that rotates in a stationary position. Our boolit has both rotational speed and linear (forward motion) speed. An engineer can calculate the RPM of a cast iron flywheel and the resulting surface feet per minute to know if said flywheel is safe at that RPM. Our boolit is adifferent story...
Let's take your 14" twist gun for our example. You know the muzzle velocity from your chronograph. So some simple calculations gives us an "RPM". IS THIS A REAL NUMBER?
Put another way..... when your boolit leaves the barrel is it in fact making ONE REVOLUTION IN 14"? How about 100 yards? I've tested a lot on these questions; so let me answer: One revolution in 14"? The boolit can make one revolution in 14" just out of the gun. BUT IT MIGHT NOT AS WELL! At 100 yards? NO! The distance traveled per revolution becomes LESS! It will continue to change and will not be 14" again! I've proven this and so has Mann over one hundred years ago. This is the definition of "going to sleep" by the way.
Would like to see how you've managed to "prove" that. It is a ballistic fact that rotational speed of the bullet degrades very, very little over the normal muzzle to target distances (0 to 1000+ yards) How do we "know" the rotation is 1 in 14" out of a 1 in 14" twist barrel? Law of physics says a body in motion tends to stay in motion unless acted upon by another force. The bullets velocity decreases because it is acted upon by another force; the air density. The rotational force degrades very, very little (there are calculation formulas for this in most ballistic books btw) because there is little to no air resistance or another force to act upon a stabilized bullets rotational speed. So out of a 1 in 14" twist barrel we can say for certainty the stabilized bullet is making 1 turn in 14" and thus correctly calculate the RPM on that.
Bottomline... Being RPM is related to distance in our case with our boolit; it is a variable in its own right and not necessarily accurate or trustworthy.
Bottom line that is an incorrect assumption. Would the bullets rotational speed slow down that quickly the bullet would then lose rotational stability at a very close range and we could not shoot the distances we do with accuracy and bullets would not have the maximum ranges they do. It is proven that the rotation sped does not slow down appreciably
Let me throw out what may be causing the proportional amount discrepancy you are seeing... I think maybe 'torsional distortion' ... Almost ALWAYS for me when I see a serious accuracy degradation with fast twists at fast speeds; and if I can find or recover a fired boolit; I see WIDER land engravings on the boolit than actual land width! This 'torsional distortion' can really mess with distance traveled per revolution!
And what then would cause this "torsional distortion" to make the bullet inaccurate by not following the line of flight? Let me answer that; "torsional distortion" imbalances the bullet by moving alloy and thus moving the center of gravity away from the center of spin. And then pray tell what causes the center of gravity not coinciding with the center of form and the center of spin to lose accuracy? Centrifugal force is what. And then where does centrifugal force come from? The answer is RPM.
Your thoughts on more 'bearing' surface on the boolit is a good one Larry... I agree if HV is the goal. But if we think what is imparting our 'spin' to our boolit, the length is short. Even 5/8" is little to guide one turn in 14" as we leave the muzzle. With a perfect boolit/rifling fit you'll guide the rotation to 1 in 14"... If you wallow out the land travel you might get anything for 1 in ??" 'Torsion distortion' is aggravated as the twist goes faster for any given velocity that initiates it.
The % of bearing surface to bullet length is not important for the reason of "imparting spin" to the bullet. It's importance comes from it keeping the bullet aligned concentrically from case to throat, in the throat through engraving on the lands and in supporting the entire bullet. The more of the bullet we have at groove diameter the less there is to bend, slough or obturate in any direction to imbalance the bullet. That long bore rider has a lot of leverage to bend, slough, or obturate it one side or the other into the .003 - .004 (usual groove depth). Also in the case of the Loverin designed bullet the lube in all those groove is not very compressible (laws of hydraulics) and supports the bearing surface as does a PP or jacket somewhat. You don't have that with the shorter bearing surface long nose bore riders. Even with a 50/50 land to groove ratio you still have 50% of the bore rider nose that is unsupported. None of the bearing surface is unsupported. Thus it is better to have more bearing surface and less nose.
I think I would add your same exact test boolits, but sized down and paper patched to the equation... I know you want to achieve a 'bare boolit' application... But this would be a good indicator if 'torsional distortion' was the culprit of your 'proportional amount' changes if they suddenly improved using a boolit with better traction!
Not necessarily so as the PP does a lot more than simply provide "a boolit with better traction". If you (I already have) tested a pure lead, a COWW and a linotype cast bullets PP'd and worked up loads from 1800 fps to 3000 fps in a 10" twist '06 you will find that even PP'd bullets have an "RPM Threshold". Actually jacketed bullets do to. The RPM Thresholds are just higher.
Your input is appreciated and has given us additional food for thought. You're actually pretty correct on a lot but are only looking at the obvious and not yet seeing the root causes. Look deeper with the laws of physics and ballistics in mind and you will see many of the "variables" we can change and affect. However, the laws of physics and ballistics we can not change but we can affect them by changing the variables.
Larry Gibson
Last edited by Larry Gibson; 06-24-2014 at 02:28 PM.
Larry,
Eutectic
Yes, I have read Mann's book and find nothing there that says the bullet RPM is faster than it is at the muzzle. Is that what you are inferring? The RPM changes very little down range and the centrifugal remains consistent. The slow increasing helical arc or the bullets flying off on a tangent to the line of flight is a result of that. We have proof of that with the results on the targets posted. I'm not sure what your trying to say?
Not necessarily Larry... The 'torsional distortion' caused by high velocity, higher pressures, and steeper twists. Maybe all three... This distortion can displace metal evenly around the circumference of our boolit by widening land engraved width. You could still be in balance but you may not stay against the lands' driving edge... Humm?
I would refer you to the test results. What you say is nice in theory and is argued ad nauseum by a couple in previous threads. The tests here disprove that the faster twists do not really raise the psi. Also if the acceleration/velocity is equal the obturation, set back, soughing or bending would be the same. Also if the bullet was "still in balance" then the centrifugal force would have nothing to act on and accuracy would be equally proportionate. Fact is if, at a given velocity, the centrifugal force will be greater in a faster twist. Thus the adverse affect on accuracy is greater. That's why the 10" twist loses accuracy at a lower velocity; the centrifugal force is greater as the RPM is greater than in the 12 or 14" twist at the same velocity.
It may be important to 'hold' our "imparted spin" as we push the envelope though???
As mentioned that is part of it.
I understand this point Larry. "Bore riders" do seem more correct for accuracy from a design
perspective... but I fight them more times than not!
Exactly! What seems "more correct" doesn't mean that it is.
As to your argument to PP, I suggest you have at it. As stated the purpose of this test is to determine the RPM Threshold of naked cast bullets of a ternary alloy. That has been done. My follow up tests have also proven excellent accuracy can be had by controlling the RPM via a slower twist, still with naked cast bullets of a ternary alloy. My intention is to see how high in velocity we can push the naked cast bullet of ternary alloy and that is my direction. There is a "Start a Thread" button. I suggest you work the PP'd bullet question since that seems your interest. I'll be glad to help on your new thread but this thread isn't the place for it.....that would make this
Larry Gibson
goodsteel
Not a problem with the 21.5" barrel on your 30 XCB. I shall be glad to help you wring out the best we can. That is the same I extend to btroj. No, I don't think they are the right twist (and yours the barrel length also) to ring out the best the cartridge may offer but I am more than willing to help prove me wrong. Be my pleasure.
Larry Gibson
Hopefully I can have a good time "wringing it out" without bringing "who's right and who's wrong" into the experience at all. I think we both agree that the rifle is right. Always has been, always will be. First thing I want to do is find the RPMTH for my 21.5" X 1-10 twist barrel and see how it compares to your results up yonder. I'm hoping to get a chance to shoot soon. I'll be sure to bring my camera.
Once that is established, I will load up and test till I flatten the primers ( I expect to be able to get nearly 2900fps before that happens), and I will document what the groups do. I expect of there is any semblance of a higher RPM/FPS accuracy potential, that I would see the patterns constrict at a certain point. If that happens, then I will experiment more right in that area. If the groups just get more and more terrible then I wouldn't think there would be anything to investigate further.
We'll see.
Maybe I'll get there by Christmas. LOL!
Last edited by MBTcustom; 06-24-2014 at 11:42 PM.
Precision in the wrong place is only a placebo.
goodsteel i for one will be looking forward to your tests with that rifle.From what little i know at this point about the rpmth you certainly have a twist rate to challenge it head on with. I guess i mean if you blow by it at some point with 1/10 twist and accuracy returns then i should be able to bring the thunder with my 1/14" easier. I fall on the rpm side of things mostly because i keep shaking hands with it at the range and Larry does such a good job of explaining what's going on that has me scratching my head at times.
If you want to take it head on to see what happens i think you made the right choice to do it with and it should be fun to try. Even if you don't find anything "beyond", your still gonna have one accurate rifle where ever it chooses to shoot at. I'll be watching this for sure and won't be dissapointed whatever the results.
Well, it sounds like we are in the same boat. I have kept an open mind on this subject for months (almost years) and after spending hours on the phone, on line, and at the range, I found there was an overwhelming amount of evidence to support Larry's position. Three of my rifles (OK, three of my barrels) have confirmed Larry's position as shockingly accurate and true. In fact, in all that time, I gave the naysayers my full, undivided attention and ear. Pretty much all I got was that Larry is wrong because Larry is just wrong. No argument that RPM is the force that acts on imbalances (three separate critics admitted this to me over the phone). No evidence to the contrary. No logical reasoning. Nothing but emotionally charged accusations and random information.
I rebarreled a rifle for one person free of charge, hoping he could provide me with something solid. I never heard anything more about this "high velocity cast boolt shooting that anybody can do." yet he continued to troll Larry, even in my threads, asking for proof while providing nothing on his part.
I built a custom scope mount from scratch for another of these free of charge, and I got the worst cussing of my life via e-mail because I wouldn't discard the RPMTH and asked for a cessation of hostilities over the issue.
I am currently building a rifle for another, free of charge, who seems to have made it his mission in life to troll any thread dealing with this issue, in spite of his horribly obvious lack of providing one shred of empirical data to the contrary (or of anything else for that matter).
Well I've had it with leprechauns with crummy attitudes and not a gold coin about their person and barely the faintest hint of a rainbow to point at. I'm interested in science and facts. I have not discounted anything that anyone has claimed, but since I have to be a hating troll in order to get that pot at the end of the rainbow, I'm going my own way and running some tests that might actually mean something to somebody with half a brain.
Since I can't stick any of these people except Larry in the same room with logical thought, then I will have to run my own tests and come to my own conclusions. My mind is still wide open, but I have accepted the RPMTH as a very valid measure of success.
BTW, I have assembled a new group of shooters. Each are true booliteers with a level head and an eye on science. They will each be provided an XCB rifle, and I have high hopes that real results will be forthcoming.
The rifles will be in 10, 12,14, and 16 twist. I took the 10 because I'm an incorrigible masochist.......obviously. LOL!
Last edited by MBTcustom; 06-25-2014 at 02:17 AM.
Precision in the wrong place is only a placebo.
Don't give up on your 8 twist rifle. You just need the proper throating and a little load delevopement.
This what a 9 twist can do at 160,000 rpm :
CBA match at Tamaqua, PA
Bottiger, Jerry, Cartidge, 7mm BR - Barrel, Shilen 23" lg, 9 twist - Weight, 12.62 lb - Scope, Weaver 36x
Bullet, NEI 170, Nose .276, Band .285 - Alloy, Lino - Primer, Rem 7 1/2 - Load, Varget 27 gr - Vel, 2000 fps
100 yd, May 2014, ave. of four, five shot groups, 1.395 - June 2014, 100 yd ave. of four, five shot groups 0.774
One very important aspect that hasn't been discused here, is barrel harmonic's and accuracy nodes. Barrel vibrations, displace shots in different positions. The barrel needs to release the bullet in the same position, each shot and unless the harmonics remain the same each shot, there will be a random displacement, regardless of twist.
The accuracy nodes are what you are looking for when you do ladder tests.
Note that of the pictured barrels, used in Larry's tests that the 10 twist barrel is the thinest of the rifles and it looks like it might even have a barrel band. It is also a a 6 groove barrel as opposed to the 4 groove of the others. I would especially call the 10 twist rifle more of a apple than a orange, regarding harmonics.
Frank
Last edited by frnkeore; 06-25-2014 at 02:23 AM.
Thanks Larry for sharing the fruits of your labor. Thank you also for not running away when folks seem to get their panties all twisted. Your insight has been helpful in a few of my own projects.
I really like to read about the experiences fro all here and then go test what works for me.
That chrony setup has me a bit intrigued. I see they don't make it anymore. I have been thinking of getting a cheap one to further my loading pursuits but reading of the unit you used in these tests makes me want to spend a lot more $$$$. Do you know of any comparable units in current production that would be of equal quality with pressure estimation capabilities?
If you think your a hammer everything looks like a nail.
Tim, are personal attacks becoming from a mod?
Don't forget that I offered to have you send the rifle in whatever form it was in and send me a bill for services rendered. You refused. Martyrdom isn't very becoming.
You will learn far more at the casting, loading, and shooting bench than you ever will at a computer bench.
I'm not martyring myself. I'm doing what I promised and keeping my end.
I'm merely stating how very disappointed I am with everyone I have talked to on the other side of this argument, and it's a little hard not to feel a little singed to be perfectly frank!
Anyway it was late at night, and I was venting.
Last edited by MBTcustom; 06-25-2014 at 07:25 AM.
Precision in the wrong place is only a placebo.
Posting Permissions
| 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 |
