Graf & SonsInline FabricationRotoMetals2ADvertise here
StainLess Steel MediaLee PrecisionTitan Reloading

Page 2 of 10 FirstFirst 12345678910 LastLast
Results 21 to 40 of 183

Thread: Cast bullet accuracy and trailing edge failure

  1. #21
    Boolit Master on Heavens Range
    felix's Avatar
    Join Date
    Mar 2005
    Location
    fort smith ar
    Posts
    9,688
    That would be interesting output from someone with the interest to do the reloading as well. I would very much like to see at least a chapter on which loads in which cartridges that go into a SEE condition, i.e., where loads are consistently smooth before and after a load causing a pressure spike. Doing that would be indicative to me as a competent job. ... felix

    What Harter66 described above would be classified as a SEE condition as well. A double shock wave would be a positive identification. I wonder how often that occurs and goes undetected, except for the crazy group at the target amongst others as good groups with the same approximate load before and after. ... felix
    Last edited by felix; 06-30-2011 at 08:09 PM.
    felix

  2. #22
    Moderator Emeritus / Trusted loob groove dealer


    waksupi's Avatar
    Join Date
    Mar 2005
    Location
    Somers, Montana, a quaint little drinking village,with a severe hunting and fishing problem.
    Posts
    16,733
    Quote Originally Posted by Michael Petrov View Post
    Everyone who shoots cast lead bullets should read Mann's book, at least once.

    http://books.google.com/books?id=QdQ...W.Mann&f=false
    Thanks for the link. I loaded it on my Kindle.
    The solid soft lead bullet is undoubtably the best and most satisfactory expanding bullet that has ever been designed. It invariably mushrooms perfectly, and never breaks up. With the metal base that is essential for velocities of 2000 f.s. and upwards to protect the naked base, these metal-based soft lead bullets are splendid.
    John Taylor - "African Rifles and Cartridges"

    Forget everything you know about loading jacketed bullets. This is a whole new ball game!


  3. #23
    Vendor Sponsor
    W.R.Buchanan's Avatar
    Join Date
    Mar 2011
    Location
    Ojai CA
    Posts
    6,561
    Bret: I have talked to this person several times and he is in person exactly like he is in print.

    When you look at his point about the technical nature of Pressure/Burn Ratio being a little above the average reader, I can easily see his point.

    If you remember when I first came to this site I started a thread called "Knowing versus Understanding". It went on for days until I got into educating people on why it works.

    The main point of that thread was to get people to study a post before reacting to what they "think" you said. IE understanding what was being said by the author, as opposed to "going off "when the read a word you didn't understand.

    You see here everyday how that went ?

    What he was saying is that most people would not put out the effort to actually read the article enough times to grasp the overall concept of the very technical subject.

    I have to agree with him on that point. They won't . They read something once a decide they know everything about what was written, or go to sleep.

    However that doesn't mean that the topic shouldn't be covered in the mag. It would just only appeal to a smaller segment of the readership that are truly interested in understanding all they know about the subject.

    Handloader and Rifle are still the best shooting related mags out there, and I get alot of valuable info from them that I feel confident in using. The reason why is that many of the writers have so much experience that they are completely consistant in their views and statements. Thus they become reliable sources for information.

    I call them, "them that knows"

    I don't always agree with everything they say but I can tell you that I have used alot of their data successfully and it has worked very well. Sources like this cut down on the work of load development considerably, just like this site does.

    Citing the Aug 2007 issue of Handloader, the Brian Pearce article on loading the .45-70 for Marlins is a perfect example. There is more useful info on loading for that caliber in one article than I have been able to find everywhere else combined.

    I have read that article 100 times easily. The average person would not do this even if the info was" Instructions on "how to $%&*"

    You've been around here long enough (14,542 posts definately says something !) that I know you agree with what I'm saying.

    Oh, and I would love to kick Hildegard in a @&& as she left my new office.

    Randy
    "It's not how well you do what you know how to do,,,It's how well you do what you DON'T know how to do!"
    www.buchananprecisionmachine.com

  4. #24
    Boolit Master
    Join Date
    Sep 2010
    Location
    Alabama
    Posts
    542
    Quote Originally Posted by Bret4207 View Post
    "The Bullets Flight" by Franklin Mann. It's a pretty good sized book, not an article. I've also seen some modern statistical type experiments done where the author said mutilated boolits made no difference, but his data showed something else altogether!

    "A stronger bullet trailing edge should result in smaller imperfections at departure, more uniform mechanical release, and thus less net off axis forces, and better accuracy."

    Well, given the choice do we want a stronger edge or a more perfect edge? I think the later. My thinking is that by the time the boolit reaches the muzzle the vast majority of the pressure has dropped significantly. Different powders.barrels lengths are going to affect this greatly. I suppose there are nifty instruments available to the scientific community to measure this and some of that higher speed stop action photography would help too.

    I mentioned a more perfect edge at the start of the last para. I've found, thanks to the boys here, that boolit bases are often not aligned with the length of the boolit. I've found they can also be seated crooked very easily, even wad cutters, and that alignment is far more important with cast than with jacketed.

    I agree with the basic idea you have, that any imperfection of the base will affect the boolit to a degree, more or less. I'm just not sure that relating it to "hardness" without specifying all the other variables involved will sit well.
    Thank you for the title/author... I'll add it to my library.


    Re "do we want a stronger or more perfect edge", I'm suggesting the answer is YES (both, but substitute "sufficiently strong" for "stronger"). If there is correlation between consistent accuracy at increasing velocities and bullet hardness (or checking), and it is for the reason I am proposing, then you want both a more perfect edge and sufficient hardness to maintain it at bullet/bore departure.

    So yes, we want the most perfect edge we can get. But if we start with a perfect edge and too soft a base edge metal at sufficiently high bullet base pressure at crown departure, then forces from angular inertia and base pressure may tend to bugger up the base edge and spoil a symmetric departure of the bullet... I suspect the largest factor in most situations would be due to asymmetric gas venting.


    This is just a theory I'm proposing here. ANY good theory should be falsifiable by a reasonable experiment. That's why I just flat out loved Molly's thread, here http://castboolits.gunloads.com/showthread.php?t=116741 ()

    In like spirit, I suggested a couple of experiments in the OP. Here are some more that could support or discount what I've proposed.

    I think you can demonstrate when and to what extent gas jetting at departure can destroy accuracy by baselining an accurate barrel/lead bullet combo for accuracy and then change only the crown at the bore. This would be done by introducing a single small nick at the bore-crown edge that will allow early/asymmetric gas venting during bullet/crown departure.

    another experiment:
    I'll bet if you create (on an otherwise well performing plain base bullet) a base edge imperfection that allows gas jetting at the crown prior to/at departure (but doesn't affect obturaton of the bore during internal bore travel), you will see significant degradation of accuracy. Also, that this degradation in accuracy will be greater than that seen from creating an imperfection at say the leading edge of the rearmost lube groove that would comparably imbalance the bullet (so if this held true, it would tend to suggest the effect isn't due as much to balance as to departure/venting).

    another experiment:
    Base edge imperfections should have less impact to inaccuracy when bullet base pressure is lower at bullet/crown departure. What if you fired the same bullet with a created base edge imperfection from the same barrel first unported and heavily ported (and fully deburred)? (oh! for the shop resources and know-how of a P.O. Ackley ).
    Last edited by DrB; 07-01-2011 at 12:52 AM. Reason: Typo

  5. #25
    Boolit Master HARRYMPOPE's Avatar
    Join Date
    Jan 2011
    Location
    Walla Walla Co. Wa.
    Posts
    1,974
    Merrill Martin did alot of experiments shooting bullets into his nail free sawdust box back in the 1980's to study stuff like this.He did stuff as weird as Dr Mann.You can find the articles in Precision Shooting and old Fouling Shots.The Mann book is dry and i believe more of a historical read(akin to Macbeth) these days.Still i have read it many times.I think the EH Harrison series in the American Rifleman on cast bullets one of the better ones for modern times.

    HMP

  6. #26
    Boolit Master
    Join Date
    Sep 2010
    Location
    Alabama
    Posts
    542
    Quote Originally Posted by Bass Ackward View Post
    What happens to a bullets base depends more on what happens to the nose and if you are accelerating it when they meet.

    The nose has to establish an air flow pattern and break the barrier. This must happen before the bullet exits and you lose control. This force determines how strong the lead has to be. So the sooner you can get airflow established, the more of the slug can remain in the pipe for strength to grip the rifling and navigate this turbulence. If you have a copper check, this can add strength at this critical launch time.

    Another issue is barrel length. Are you still accelerating the slug or is it up to speed? Cause with what is happening to the nose when it hits air, (friction) you could begin to strip the base as only some of it remains in the pipe. (acceleration force) Now you are gas cutting.

    All of this goes to the old analogies of: shoot the heaviest for caliber bullets possible (longest), use the longest barrels for lead, and shoot fast powders so that acceleration is done before exit and pressure has been dropping to affect the base.

    Obviously nose shape (design) plays a role in what you need from a design / hardness level.

    It's all in the launch.
    BA, I've had years and years of fluid dynamics (so I would hope that I would have the capacity to understand what you are saying eventually if we iterate)... But I really don't understand what you are saying above you think is happening?

    Stagnation pressure on the nose of the bullet at say 1800 fps would be something less than 64psi from freestream flow, and generally much lower (prior to muzzle blast... and I would suspect probably less than 64 psi due to the surrounding gases at the nose of the bullet already moving with/past the bullet -- that is, it isn't really freestream flow at the nose even when the nose has poked out past the crown).

    On the base of the bullet I would expect anything from at least one to two orders of magnitude more pressure (10x60psi to 100x60psi or more) from the combustion gases, depending. It would be interesting to check this with an internal ballistic computer as I am just throwing that out as a swag, but my point is that I really think venting at departure, muzzle whip timing of departure via bullet velocity, and post departure flight with an upset or unbalanced bullet have more to do with accuracy than variations in the free air flowfield around the bullet nose just prior to departure. The magnitude of the forces just shouldn't be large enough, I think, to be of comparable significance?

    Maybe I could understand what you are getting at better if you related the sort of things you've physically seen that you think are explained by your post?

    Best regards, DrB
    Last edited by DrB; 07-01-2011 at 10:48 PM. Reason: Edited for clarity

  7. #27
    Boolit Master
    Join Date
    Sep 2010
    Location
    Alabama
    Posts
    542
    Quote Originally Posted by HARRYMPOPE View Post
    Merrill Martin did alot of experiments shooting bullets into his nail free sawdust box back in the 1980's to study stuff like this.He did stuff as weird as Dr Mann.You can find the articles in Precision Shooting and old Fouling Shots.The Mann book is dry and i believe more of a historical read(akin to Macbeth) these days.Still i have read it many times.I think the EH Harrison series in the American Rifleman on cast bullets one of the better ones for modern times.

    HMP
    Is there a way to get a compilation (other than by hand scanning at the library) or at least a list of his articles by date? Is the american rifleman available as a digital archives?
    Last edited by DrB; 07-01-2011 at 01:42 AM.

  8. #28
    Boolit Master
    Join Date
    Sep 2010
    Location
    Alabama
    Posts
    542
    Quote Originally Posted by Harter66 View Post
    I suppose the premise i'm applying is fast powder,fast peak,harder boolit hit,more deformation. My above are all plainbased for the record. My suspicion then, was that the powder was peaking out pressure wise and spiking or outrunning its abilities. I lack the terms here but the pressure was no longer pushing the boolit, but pacing it,the causing a double shock wave at the muzzle. So the boolit was pushing 1 as well as being overtaken by 1 then passing through it again.
    Interesting results! Thanks!!!

    So regarding the double shock, thing. Compression waves turn into (condense into) shock waves when we're talking about significant changes in pressure communicated by the wave. This is because when you compress a gas you heat it, heating it raises the speed of sound, and any following compression waves are going to tend to catch up with the leading waves until they condense into a shock.

    So when the combusting/expanding gases are communicating pressure up the bore to the base of the bullet, it is happening as shock waves all the time. They are ubiquitous. Expansion waves are likewise being communicated from the base of the moving bullet back down the barrel to the chamber (there's no such thing as an expansion shock because an expansion wave lowers the speed of sound).

    Now, about what you observed with your loads. That sounds consistent to me with the idea that accuracy tends to be destroyed when the stress imparted to the bullet metal (by the rifling trying to impart angular acceleration/spin) exceeds the stress the bullet metal can withstand. The engraved lands start opening up (taking up more and more of the bullets circumference instead of just the physical rifling land width).

    Faster burning powders can kick a bullet so hard initially that the rifling skids, you get poor obturation and maybe some of the asymmetric venting departure effects I've been suggesting. A slower burn rate may let you push to higher velocities by not over torquing the engraved lands on the bullet. A slower yet powder may let you get faster still. I don't see how your observations necessarily are contrary to what I was proposing in the OP.

    Best regards,
    DrB
    Last edited by DrB; 07-01-2011 at 01:40 AM.

  9. #29
    Boolit Master 303Guy's Avatar
    Join Date
    Oct 2008
    Location
    New Zealand
    Posts
    7,848
    Here is flame cutting that occured quite far up the boolit shank.



    All the leaking gasses got channeled into one jet by the groove in the boolit maybe?

    I've discovered that a light load very fast powder can expand a case neck more than a stiffer charge of slow powder. Primer flattening supports the supposition that pressures were very mild indeed. How do I know the necks were expanding more? Rust damage in the neck area of the neck was gripping those case necks which doesn't happen with more powerful and higher pressure slow powder loads.
    Rest In Peace My Son (01/06/1986 - 14/01/2014)

    ''Assume everything that moves is a human before identifying as otherwise''

  10. #30
    Perma - Banned


    Bret4207's Avatar
    Join Date
    Mar 2005
    Location
    St Lawrence Valley, NY
    Posts
    12,931
    Quote Originally Posted by W.R.Buchanan View Post
    Bret: I have talked to this person several times and he is in person exactly like he is in print.

    Arrogant and egotistical?

    It make take the average HL reader a couple times going over something, but I think raising the bar rather than lowering it is a worthy idea.
    Last edited by Bret4207; 07-01-2011 at 12:32 PM.

  11. #31
    Perma - Banned


    Bret4207's Avatar
    Join Date
    Mar 2005
    Location
    St Lawrence Valley, NY
    Posts
    12,931
    Quote Originally Posted by DrB View Post
    Thank you for the title/author... I'll add it to my library.


    Re "do we want a stronger or more perfect edge", I'm suggesting the answer is YES (both, but substitute "sufficiently strong" for "stronger"). If there is correlation between consistent accuracy at increasing velocities and bullet hardness (or checking), and it is for the reason I am proposing, then you want both a more perfect edge and sufficient hardness to maintain it at bullet/bore departure.

    So yes, we want the most perfect edge we can get. But if we start with a perfect edge and too soft a base edge metal at sufficiently high bullet base pressure at crown departure, then forces from angular inertia and base pressure may tend to bugger up the base edge and spoil a symmetric departure of the bullet... I suspect the largest factor in most situations would be due to asymmetric gas venting.


    This is just a theory I'm proposing here. ANY good theory should be falsifiable by a reasonable experiment. That's why I just flat out loved Molly's thread, here http://castboolits.gunloads.com/showthread.php?t=116741 ()

    In like spirit, I suggested a couple of experiments in the OP. Here are some more that could support or discount what I've proposed.

    I think you can demonstrate when and to what extent gas jetting at departure can destroy accuracy by baselining an accurate barrel/lead bullet combo for accuracy and then change only the crown at the bore. This would be done by introducing a single small nick at the bore-crown edge that will allow early/asymmetric gas venting during bullet/crown departure.

    another experiment:
    I'll bet if you create (on an otherwise well performing plain base bullet) a base edge imperfection that allows gas jetting at the crown prior to/at departure (but doesn't affect obturaton of the bore during internal bore travel), you will see significant degradation of accuracy. Also, that this degradation in accuracy will be greater than that seen from creating an imperfection at say the leading edge of the rearmost lube groove that would comparably imbalance the bullet (so if this held true, it would tend to suggest the effect isn't due as much to balance as to departure/venting).

    another experiment:
    Base edge imperfections should have less impact to inaccuracy when bullet base pressure is lower at bullet/crown departure. What if you fired the same bullet with a created base edge imperfection from the same barrel first unported and heavily ported (and fully deburred)? (oh! for the shop resources and know-how of a P.O. Ackley ).
    I agree. but I think there's more to it than JUST another "harder is better" theory. Crown condition, rifling depth and condition, rifling form and variations, pressure curve, base style and diameter and base diameter vs groove depth are a few of the variable I can think of. And then there's alloy composition and barrel condition too. There are more I'm sure.

    I'm not fighting your idea, I just think you need to include the other factors too. If it's just "harder is better"... well, they make jacketed bullets for that.

  12. #32
    Boolit Master
    Join Date
    Mar 2005
    Location
    US, Wash, PA
    Posts
    4,867
    Quote Originally Posted by DrB View Post
    Maybe I could understand what you are getting at better if you related the sort of things you've physically seen that you think are explained by your post?

    The real problem with understanding is the magnitude of influences that occur in trying to replicate exactness too understand.

    1. We know that going up through the barrier is destabilizing and coming back through it as well.
    I got that from a 50s TV show on Joe Walker about design problems. (neighbor) And the barrier is broken at the muzzle. You will hear the fracture as you run ladder testing. You go from poom to crack. Not only do you have force, but friction and heat.

    2. Accuracy zones (with velocity) goes up as bore diameter declines regardless of twist rate. 45 caliber is 1300 fps and 22 caliber is where you want it really. Strange thing is that pressure drops (muzzle pressure the least) most in 45 caliber and least in 22. Think about that one as it covers your proposed testing.

    3. If you bring pressure up slowly enough with a PB so as not to ruin a base, then pure lead will fail at one velocity and you can get more velocity as you harden. The narrowest window again is 45 caliber where you have very little advantage to over harden and the widest 22 where hardening pays off big time.

    4. In the same caliber, accuracy points decline (in velocity) as twist rate increases.

    5. I ran penetration testing in gelatin awhile back using pure lead on a 150 gr spitzer design to cut back on the amount of gelatin needed. What I found was that penetration dropped and became erratic as velocity increased beyond the bullets ability to hold during launch. Bullets did not mushroom from the spitzer design really, but I concluded that as velocity increased RPMS were actually dropping, thus the loss of stabilization. The gas checks appeared to hold the rifling, but rotated on the base. (no longer aligned with the bullet) If you picture that in your mind, there is only one way it can happen really.

    That's from too many years of experience.
    Last edited by Bass Ackward; 07-01-2011 at 07:10 AM.
    Evaluate everything you read for safety and use common sense.

  13. #33
    Boolit Master on Heavens Range
    felix's Avatar
    Join Date
    Mar 2005
    Location
    fort smith ar
    Posts
    9,688
    We can never assume the effective boolit "twist" at launch is ever equal to the "barrel" twist, except maybe when the target consistently displays consistent groups. Even then, it would be nice to know the boolit's actual rotation just for the fun of it (proof?). ... felix
    felix

  14. #34
    Vendor Sponsor
    W.R.Buchanan's Avatar
    Join Date
    Mar 2011
    Location
    Ojai CA
    Posts
    6,561
    bret: I agree that raising the bar should be the intended goal of any magazine, and they all profess to be educating the masses in their own ways.

    I personally think that the articles I requested would appeal to a larger number than what Scoville thought, and if explained in a manner that was understandable to more people, (IE using discriptive terms that are more easily understood than the strictly technical jargon that the "scientifics" use) would certainly be useful in raising the bar you spoke of.

    I understand the point about arrogant and egotistical, but I personally feel that those terms only apply to those who can't back up what they say with some significant level of expertise.

    Regardless of what you think of him, Muhamad Ali/Cassius Clay was arguably the greatest Boxer of all time. Reason being he pretty much did what he said he was going to do.

    Now if you really want to talk arrogant and egotistical you need look no further than our current president. He is the very personification of the words. :takinWiz:

    I don't think Scoville rises to that level, although in his case, speaking from his 50 years of experience, anyone could become a bit jaded when answering the same questions for the thousandth time. I would classify him more as "gruff and firm in his convictions".

    I can see how you might not like his tone, but you can't argue with his qualifications.

    Randy
    "It's not how well you do what you know how to do,,,It's how well you do what you DON'T know how to do!"
    www.buchananprecisionmachine.com

  15. #35
    Boolit Master on Heavens Range
    felix's Avatar
    Join Date
    Mar 2005
    Location
    fort smith ar
    Posts
    9,688
    Yes, Randy, there is no real argument in what you have said, but I will say trying to explain something to anyone without having the experience to comprehend/understand is useless. For this reason I agree with Scoville. If he should do such an article, it would be best for it to be published somewhere else, like in Precision Shooting, or in a professional periodical dealing with thermodynamics or something similar. ... felix
    felix

  16. #36
    Vendor Sponsor
    W.R.Buchanan's Avatar
    Join Date
    Mar 2011
    Location
    Ojai CA
    Posts
    6,561
    Felix: There was an article published in a more recent Handloader by a guy who was attempting to quantify the efficiency of different powders with relation to different cartridges. All .30 caliber cartridges of one style or another ranging from .30x1.5 to.30-378

    At least that's what I think he was trying to do?

    The article was 5 pages long and contained a bunch of graphs.

    I have no idea what the results of this "experiment" was as the last paragraph makes very little sense.

    I have tried to read this article several times only to get bogged down by nebulous terms the meaning of which, can not be extrapolated from the context. And I doubt they were used correctly anyway.

    In fact he did state the results of this test. "Velocity is a function of case capacity" "Some cartridges are more efficient than others" My reaction was NO S*&%?

    Point is for such a technical article a Glossary of terms should have been included and the editor should have simplified the content to where the actual results would have been a little easier to deduce.

    Taking such lengths to state an obvious fact tells me this guy really doesn't understand all he knows about this subject. In the end he couldn't apply an "efficiency number?" to each cartridge so you could tell what the relative efficiency betweeen cartridges was. So what was the point?

    "Some were more efficient than others" really didn't cut it.

    Even with my limited knowledge of the nuts and bolts of Handloading I was able to deduce that I would not be using any data published by this guy. I don't believe he knows what he is talking about.

    If you actually know what you are talking about (any subject whatsoever) you should be able to transfer that knowledge in clear concise terms that your audience will understand. This was NOT accomplished in this article.

    Brian Pearce, Mike Venturino, John Barsness, Dave Scoville, John Haviland, Charles Petty and others who contribute to those mags, can do this.

    As a result I consider them to be "them that knows"

    Charletons typically try to use at least one undfinable term in every sentence. This insures that unless you know the meanings of the words they are using wrongly, or know the subject better than they do, that you can't tripp them up. (read that as , bedazzled by BS) most people won't say anything. But some will and this is how I have been able to avoid the Liberal Mind-rape of living in CA for 55 years.

    Maybe you're right and that type of article would be better served in a more technically oriented source. My problem is,,, I thought Handloader was that source.

    Randy
    Last edited by W.R.Buchanan; 07-01-2011 at 05:53 PM.
    "It's not how well you do what you know how to do,,,It's how well you do what you DON'T know how to do!"
    www.buchananprecisionmachine.com

  17. #37
    Perma - Banned


    Bret4207's Avatar
    Join Date
    Mar 2005
    Location
    St Lawrence Valley, NY
    Posts
    12,931
    Randy, I can accept gruff and jaded. Scoville used to write some really good articles as did guys like Jim Carmichael, Rick Jamison, of course Ken Waters, Mike V, and Al Miller. Somewhere along the line HL simply got dumbed down a notch. Having most of the issues from #1 on you can see the progression. It saddens me when the current editor has no interest in putting the mag back up to it's former level.

    Guys like Felix (an actual, honest to God rocket scientist!) and Dr B with their scientific background can often interpret for us lesser beings what the Mr. Spocks of the world are trying to say. Handy to have guys like that around!

  18. #38
    Boolit Master
    Join Date
    Sep 2010
    Location
    Alabama
    Posts
    542
    Quote Originally Posted by Bret4207 View Post
    I agree. but I think there's more to it than JUST another "harder is better" theory. Crown condition, rifling depth and condition, rifling form and variations, pressure curve, base style and diameter and base diameter vs groove depth are a few of the variable I can think of. And then there's alloy composition and barrel condition too. There are more I'm sure.

    I'm not fighting your idea, I just think you need to include the other factors too. If it's just "harder is better"... well, they make jacketed bullets for that.
    Bret, I didn't think you were fighting the idea. I do not believe anything about ballistics is "simple" except when a large number of things are already pretty close to perfect.

    I'm not trying to propose a grand unified theory of cast bullet accuracy. As I mentioned, I loved Mollys thread, and not only can the theories she's proposed appeal to me, I can go out and try to test them for myself as she has proposed.

    I've been doing a lot of reading on cast boolits and elsewhere lately, and was wondering about the correlation between increasing velocity and increasing hardness (or checking) with accurate loads. The analog of an imperfect crown with an imperfect bullet base got me wondering as to how much base edge quality at departure might explain.

    And no one has to worry about getting me riled. Reality is. I hope someone (or us collectively) has data they are willing to share that would support or discount this particular notion. There is always something new to learn (or unlearn).
    Last edited by DrB; 07-01-2011 at 11:39 PM.

  19. #39
    Boolit Master
    Join Date
    Sep 2010
    Location
    Alabama
    Posts
    542
    Quote Originally Posted by felix View Post
    We can never assume the effective boolit "twist" at launch is ever equal to the "barrel" twist, except maybe when the target consistently displays consistent groups. Even then, it would be nice to know the boolit's actual rotation just for the fun of it (proof?). ... felix
    Can't you have pretty stout proof in the form of a recovered bullet with engraving marks intact? As long as there isn't evidence of skidding/stripping, you should be able to calculate nominal spin rate.

    Engraved groove depth as compared to rifling width should even allow you to calculate a maximum error (minimum spin rate) with a few assumptions? Haven't quite thought this through enough to propose a formula when there is widening of the lands evident.

    Nominal spin rate in rotations per minute = (velocity ft/sec)/(twist inch/turn)*(12 inch/ft)*(60 sec/min)

    For experimental measurement you could do high speed photography with a marked bullet, measure total reflected light levels from a scene with a marked bullet vs. time, or you might be able to do it acoustically with a symmetrically spooned nose or such. Probably not necessarily cheap but very doable if you had a budget.

  20. #40
    Boolit Master on Heavens Range
    felix's Avatar
    Join Date
    Mar 2005
    Location
    fort smith ar
    Posts
    9,688
    Time + Money + an obnoxious attitude for an objective = accurate results. Most folks give up too soon for one reason or another, either good or bad. My experience has been not obtaining external ideas to get over an unexpected hurdle. The real excuse for many of these projects has been no profit potential for the results.

    You are correct in using a "photo" apparatus for measuring the rotation. The boolit would have to be painted with something "hot" that can be read with the existing particle measuring devices. Finding an appropriately short half-life paint would be prohibitive???? Who wants a forever contaminated barrel? ... felix
    felix

Page 2 of 10 FirstFirst 12345678910 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
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