The fellow who doesn't think the earth is flat has never been to Kansas.
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The fellow who doesn't think the earth is flat has never been to Kansas.
Quote:
Originally Posted by Larry Gibson
Perhaps you should tell Char-Gar his rifle will shoot the 165 gr. and above better than he said. Seems his results didn't match yours.Quote:
Originally Posted by Char-Gar
All most people understand is that they can't get accuracy the way they're doing things above a certain level. Tolerances, not an unsubstantiated notion is the cause. Most folks who don't understand why they're having a problem will latch onto something that sounds reasonable........ The same way you did. Remove the poor tolerances and the problem simply disappears.
goodsteel is the resident gunsmith who deals in very small tolerances in barrel work. Ask him about some of the factory barrels he encounters. Really atrocious barrels...........
If you or anyone else wants to put a custom barrel on his firearm, spend that money then.... anyway you want, but some or most of the folks here would be quite hard pressed to do that too often. You tell them they can push a fictitious made up name for an equally unproven theory (I can supply the link to where you said this in a post BTW... and anyone is welcome to PM me for it) to get accuracy over about 1800 or so by buying a slow twist barrel. Yep, just trade money for learning something...........works every time. Government does that a lot and we all see where that goes. The point is that accuracy happens when you start and keep a cast boolit straight in the barrel, from loading to exit of the barrel instead of tipping it right in the cartridge neck upon ignition and sending it down the barrel out of line to produce the symptoms you've described.
the "Gap" is flat all right!Quote:
Originally Posted by Nrut
I didn't understand the RPM threshold concept until I ran into it twice trying to get a 30-30 to push a boolit thru a 1/10 twist tube @ factory load velocities. Tried lots of things, didn't work, didn't know why. Pretty ugly "groups"; blamed the rifle, blamed the scope. Scope had issues but it was the load all along. Shooting buddy was shooting the same boolit @ 1600 fps and getting awesome groups, I backed off to 1800 and groups greatly improved.
I may be wrong but it seems to me it's more about physics than it is about careful blueprinting of rifles and loads. We can't get something as stupid as Obamacare repealed, not a chance of changing the laws of physics.
I'm a competitive target shooter in ASSRA & ISSA and while I shoot at velocitys under 1650 fps, I always match the bullet length to the twist rate in my competion rifles and use the slowest twist that keeps the bullet point on at 200 yards. By that, I'm always under the so called "threshold", I do have some points and questions relating to this though.
1. I have seen excellent scores and groups shot with 30 cal, 10 twist, ~2000 fps match rifles in CBA matches.
2. If it can be done in even one rifle, reliably, it can be done in any 10 twist with the same setup.
3. A match chambering and quality barrel can and will shoot better than a "factory" chambering and barrel. The throat means almost everything with cast bullets. You will NEVER find a match winning cast bullet target rifle with a "factory" throat.
4. You really need to define accuracy when it comes to these blanket statements. What is the inaccuracy that you speak of when the bullet crosses the "threashold" or what is the maximum accuracy to be expected of bullets that cross the threshold? I see threshold as a subjective term that can be defined in any number of ways and thus a fairly safe term to use if other's results doesn't fit your ideology.
5. I have never seen it (threshold) defined regarding what actually happens to the cast bullet that causes the inaccuracy. Since PP bullets seem to be considered immune to it, even though they are cast also, why aren't they subject to it?.
6. I have only one experiance in this matter. Scoped M48, original chambering and barrel, floated 9.5 twist barrel in a slightly shorten stock. WC 852, 2157 fps, original Lyman 323471, 215 gr w/GC bullet in #2 alloy, reformed '06 LC brass. It will average 2", five shot groups (4 five shot average) at 100 yards. What would the groups be if it was under the "threshold"?
Frank
frnkeore
5. I have never seen it (threshold) defined regarding what actually happens to the cast bullet that causes the inaccuracy. Since PP bullets seem to be considered immune to it, even though they are cast also, why aren't they subject to it?.
Obviously your coming in late on the RPM threshold discussion. I have discussed and answered the question as to the cause of inaccuracy (centrifugal force) when the cast bullet crosses the RPM threshold. The PP'd cast bullet is indeed subject to the RPM threshold especially with softer alloys. However many times the RPM threshold will be above the velocity/RPM attainable by the cartridge/bullet/barrel length combination used. The RPM threshold will occur at a higher velocity/RPM because the PP'd cast bullet is much better supported in the barrel and maintains it's balance much better and to a much higher acceleration rate.
A search of a lot of my posts in numerous threads will give you a much more detailed description of how higher RPM can cause inaccuracy. A study of ballistics will do the same or simply reading the accuracy section in the Hornady manuals will provide a simplified answer.
6. I have only one experiance in this matter. Scoped M48, original chambering and barrel, floated 9.5 twist barrel in a slightly shorten stock. WC 852, 2157 fps, original Lyman 323471, 215 gr w/GC bullet in #2 alloy, reformed '06 LC brass. It will average 2", five shot groups (4 five shot average) at 100 yards. What would the groups be if it was under the "threshold"?
May be that your load is still under the RPM threshold for that bullet/load combination. Question is does the same load average the same 2 moa at 200 yards? If not and there is non linear expansion of the groups then that load has exceeded the RPM threshold. The farther over the RPM threshold the larger the non linear expansion will be. Going over the RPM threshold does not mean the bullet loses stability and all accuracy is lost.
That 323471 is a very well designed Loverin style bullet and one can push the RPM threshold upwards with it. I can push it also to 2150 fps with 2 moa accuracy and be right at the RPM threshold. It has one of the highest BCs for cast bullets that will shoot well at higher velocity and is a favorite of mine for longer range shooting (600 yards). However, if I back it off to 1850 fps it shoots 10 shot groups right at 1 moa at 100 and 200 yards out of my own 24/47.
Larry Gibson
1. I have seen excellent scores and groups shot with 30 cal, 10 twist, ~2000 fps match rifles in CBA matches.
In support to the above statement, I offer this, shot at the CBA Nationals, this year:
http://www.castbulletassoc.org/br/20.../nationals.pdf
Craig, Frank
Soquel, CA
HVY class
Cartridge, 30BR
Barrel, Shilen, 26" lg, 10 twist
Action, Shilen DGA
Scope, Tasco 36X
Weight, 13lb 14oz
Mold design, Eagan 215gr
Alloy, Lino
Base dia. .310, Nose, .300
Lube, Texaco Turax
Powder, N 135, Charge 28.0, Primer Rem 7 1/2
Velocity, 2020 fps chronographed
Score targets
199 5x 100 yds
184 1x 200 yds
383 6x combined score
5 shot groups
0.564 100 yds
1.490 200 yds
0.654 MOA for 100 & 200 yds combined
10 shot groups
0.677 100 yds
2.356 200 yds
0.928 MOA for 100 & 200 yds combined
How is this possible?
4. You really need to define accuracy when it comes to these blanket statements. What is the inaccuracy that you speak of when the bullet crosses the "threashold" or what is the maximum accuracy to be expected of bullets that cross the threshold? I see threshold as a subjective term that can be defined in any number of ways and thus a fairly safe term to use if other's results doesn't fit your ideology.
You didn't address the above. But, what you say below, seems to comfirm my last sentence.
Obviously your coming in late on the RPM threshold discussion. I have discussed and answered the question as to the cause of inaccuracy (centrifugal force) when the cast bullet crosses the RPM threshold. The PP'd cast bullet is indeed subject to the RPM threshold especially with softer alloys. However many times the RPM threshold will be above the velocity/RPM attainable by the cartridge/bullet/barrel length combination used. The RPM threshold will occur at a higher velocity/RPM because the PP'd cast bullet is much better supported in the barrel and maintains it's balance much better and to a much higher acceleration rate.
I'm probably not the only one that has come late to this theory so, I'm sure others would also like to know.
The RPM threshold will occur at a higher velocity/RPM because the PP'd cast bullet is much better supported in the barrel and maintains it's balance much better and to a much higher acceleration rate
1. How is the PP supported much better than a cast bullet?
2. So, ballance is a key issue and a well cast, round bullet will be the same in that department as PP?
3. Explain the Acceleration issue, please and why PP is better at withstanding it.
4. Most PP bullets are cast bullets and some like Lyman are cast with grooves to hold the paper, what makes them able to do things that grooved bullets can't? Paper has no ridgity like jacketed bullets and the paper can can leave the surface of the bullet at different points in fight.
Frank
PS
Check out the 10 twist production class rifle accuracy in the CBA link
"That 323471 is a very well designed Loverin style bullet and one can push the RPM threshold upwards with it. I can push it also to 2150 fps with 2 moa accuracy and be right at the RPM threshold. It has one of the highest BCs for cast bullets that will shoot well at higher velocity and is a favorite of mine for longer range shooting (600 yards). However, if I back it off to 1850 fps it shoots 10 shot groups right at 1 moa at 100 and 200 yards out of my own 24/47."
Tell us why this multigroove bullet can be push faster than than the normal "threshold". I had figured that the PP got most of it's advantage from the lack of grooves. This bullet is is way above your threshold at 2150 in a 9.5 twist and should preform worse than say a 2 groove bore rider when compared to a PP.
Frank
Nobade sounds like you have yourself a fine cast bullet launcher, have fun and enjoy and thanks for reporting.
I see this a lot here:
the issue of alloy and tensile strength is important
A cast boolit has NOTHING to do with tensile strength. A cast boolit is subjected to compression, shear and twisting. Those parameters involve compressive, shear and torsional strengths in a lead alloy...... not tension. Helps to know the actual psychical properties involved thru training and testing in a lab by people who teach these things, not reading out of a book yourself or guesstimating what happens.
I'm just hanging around waiting for pics of Nobade's new rifle!
+1 and a few pics of targets:)Quote:
Originally Posted by TXGunNut
OK, as soon as I get some time to go out and play with it I'll get some pics. Had to work extra this week so the rifle is kind of lonely but soon I'll get it out to the range again.Quote:
Originally Posted by swheeler
-Nobade
Watch out for a lonely rifle, she'll cheat on ya!;)
Helps to spell properly so your argument isn't laughable at 1st glance. "psychical properties" is a rather poor malapropism for "physical properties". By the by, you may wish to read, reread and continue to read the 1st statement of your siggy until the irony of it all sinks in.Quote:
Originally Posted by 45 2.1
frnkeore
Obviously you're looking for another argument?
Won't get one from me but if your questions are sincere you could do simply as I stated and use the "search" function of this forum. Use "RPM threshold" as the key words and "Larry Gibson" as the poster. Check "any date" and then click on "search". You will find more than enough reading on the topic to answer your questions and keep you busy for a while.
For starters I'll help you out a bit and you might read this thread as it also answers your questions; http://castboolits.gunloads.com/show...=RPM+threshold
Larry Gibson
I am not looking to argue, I'm looking for facts.
Ok, after reading the above referenced thread, here is what I think about your threshold........... It's really not a threshold at all. You make exceptions to your own 120K - 140K rpm in many ways to make it still seem like it applies, such as the Loverin designs can push it up. The Loverin design by it's very design should push the threshold down, since it has lots of grooves, each one able to impart a imbalance, not only that but, the actual mold can cast out of round and can't be brought back to center by sizing.
The real limiting factor to velocity and twist is how well the load combination is assymbled and the harmomics it imparts on the barrel. With a well cast, round bullet assumed.
You've posted many times that the reason that someone isn't getting accuracy is because they've crossed your threshold when it could mearly be that the bullet is misaligned upon ignition and there can be many reasons for that. You also state that the powder speed effects your threshold considerably. If it is indeed a limiting factor in will have a real limit, not something that can be pushed around to fit your theory. Your limit is actually the misalignment and distortion associated with getting the bullet from the case into the barrel along with a lube that will keep it from damage as it travels through the barrel. PP is what does the latter best. I never PP because it wears the barrel. I shot PP slug guns for 3 years and that's why I know it occures and won't use them now, my barrels are dear to me.
If you want to shoot accurately at higer velocitys, you need a close fitting neck ,.0005 - .001 Max clearance in your chamber neck with your case neck to bullet fit. You need a freebore of about .1 -.2 (depending on number of bands) at .000 to no more than .001 over groove diameter and you need a long lead of .5 to 1 degree per side, plus a good lube for that purpose.
The reason that the 311299 shoots so well in milsurp and production rifles, is that the nose aligns itself to the bore and the large base bands fill the neck and throat fairly well, the only bad thing is that the steep throat angles and having to be swaged to .308 can cause distortion. The short Loverin (311465-6) shoot well in a 308 because the 308 has a freebore they can be fitted to and in the case of the 8mm, it has a very long lead (.43 deg) that can help align the 323470 & 471. The loverin has lots of lube but, you have to inspect the bullets carefully for flaws.
I do agree that you shouldn't spin them anymore than you have to, to minimize centrifical forces. I only shoot production (milsurp & production sporting) rifles for fun. I build and shoot my own match rifles for accuracy and match the bullet length and shape to the rifling twist. In 30 cal I use 12, 13 and 14 twist as I have no molds that need quicker twists but, as the results that I posted prove that you can shoot at 2000+ fps with a 10 twist and still get competitive accuracy, it disproves the "Thereshold" theory and shows that the bullet alignment, lube and fit have more to do with it than RPM. Competition is how you find limits and thoughs limits will alway be pushed in anyway the competitor can think of.
Attending and shooting in matches (especially CBA, ISSA & ASSRA) will enlighten you in many, many ways regarding BR accuracy.
Frank
Your limit
Frank
There in lays the problem with your analysis. The RPM threshold is not a "limit" at a specific RPM. It indeed can be pushed up or down with any given bullet of any reasonable fit. If it's not a factor then with all your experience at "The real limiting factor to velocity and twist is how well the load combination is assymbled (SP) and the harmomics (SP) it imparts on the barrel. With a well cast, round bullet assumed. perhaps you can enlighten us on how you shoot cast bullets accurately, out of say your 8x57 at 2400+ fps? How about the paltry '06 with a 170 - 180 gr cast at 2700 fps? You are correct in those things do have a bearing on pushing the RPM threshold upwards as does using a slower burning powder for the cartridge. There are other things involved like bullet design. The Loverins do so well because the most often have minimal noses and fit the case from base of the neck, the throat diameter and just bump the leade. They leave little room for unwanted obturation just as the Eagan designed bullet and the LBT designed bullets do.
Consider that Mr. Craig, with his heavy bench rest rifle very carefully made and with very precision reloading technique using the best of benchrest equipment of probably precisely cast and selected cast bullets managed to push the RPM threshold for a 10” twist rifle a whole 70 fps. Are you telling us, like a couple members and one former member, that joe average reloader/caster with his stock M1903 milsurp ’06, surplus cases and cast bullets from straight COWWs is going to even come close to pushing the RPM threshold at all let alone even 70 fps using “the load” of either Red Dot or 2400? O even with his M70, M700, Savage or other factory rifle?
I’ll refer you to post #1 in http://castboolits.gunloads.com/show...velocity-chart. I explain all this again and include all that you mention is necessary. Perhaps if you want to reiterate 45 2.1s and his cohort, starmetal's arguments you should read all the threads and posts that come up in a “search”. I also suggest you go back and read my posts in the 1st suggested thread because they do answer all your questions and suppositions you have reiterated here.
Many here are very tired of the same old arguments proffered by a few against the RPM threshold. If you can shoot cast bullets accurately at high velocity then tell us how you do it and be prepared to prove it in front of reliable witnesses. Myself and bass ackwards worked diligently with a 311291 (not known for HV accuracy out of fast twist barrel) use my mould which I’m sure 45 2.1 will tell us all again how crappy it is. None the less both myself and bass were able, through proper loading techniques, to push the RPM threshold up over 2200 fps and maintain 2 moa or less accuracy from standard factory 30-06s with 10” twists so it can indeed be done. I have also pushed the RPM threshold with Lovern style (323471 in my own 8x57) and LBT bullets in the .308W and the .223 specifically and with other cartridges.
Consider this; if there was not a reason that regular cast bullets can’t be shot at the same high velocities as PP’d or jacketed bullets out of faster twist barrel they would be shot at the same high velocities. They would now wouldn’t they. Fact is they are not. There is a reason for it. A reason based on sound physics and ballistics, not conjecture.
It appears you have not read my answers or posts in the suggested thread. Had you actually read those you would have your answers. If you object to what I say then say so and prove otherwise instead of hypothesizing. Please don’t keep asking the same questions over and over as you have the answer to them from me. As they say, if you don’t like the answer don’t ask the question. That is, unless you are really just looking for another argument.
Larry Gibson
Nobade good choice on the twist rate, enjoy!;)
Excellent subtle suggestion, let's keep the thread on topic.Quote:
Originally Posted by swheeler
Larry Gibson