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Thread: Trailing Edge and accuracy

  1. #1
    Boolit Master
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    Trailing Edge and accuracy

    Hope to get some discussion and enlightenment. I have always read about the importance of a good barrel crown for an accurate rifle. The question is " Is the trailing edge of the Bullet which should be just the reverse of the crown as important as the barrel crown?" Has anything been done in the past to enhance or improve the trailing edge to improve accuracy other than adding a gas check?

  2. #2
    Boolit Master
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    I am not sure what you mean by "reverse of crown" but bullits have bevel base, boat tail, and nose pour and adding a few wads to improve accuracy.

  3. #3
    Boolit Master JBinMN's Avatar
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    I would say that it does. Look at "boat tail" bullets. They are designed so the trailing edge of the bullet has low drag. That is just one example of the shape of the base having an effect on the speed & accuracy. So, IMO, the base of bullets, and particularly cast boolits should be inspected just as much for imperfections as well as the rest of the boolit. Seems to me that a bullet that has a chunk missing on the base wile also have an effect on it when flying thru the air due to it being out of balance & an effect on the drag/B.C. I am not expert though, just using what I thought would be a comparison to help with your question. I think it does have an effect.
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  4. #4
    Boolit Master

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    Casting your bullet and maintaining a sharp square clean edge is one. Rounded edge or dinged up can have a detrimental effect same as a bad crown. Even the bevel base if not true and clean can cause problems. A mould that casts a square true clean base is a big plus. This is one reason for nose pour moulds, bases are square and done correctly the base is sharp as a knife edge. I modified a 535 grn 45 cal lyman postell mould from base pour to nose pour. Accuracy improved compared to bullets cast with the same mould before converting. Bases looked like glass on the bottom no sprue marks or imperfections Base appeared slight more square on the comparator and edges were very sharp and crisp, compared to the ones cast before. The conversion took away a little of the radious on the nose for a small flat. Was an interesting experiment on this mould.

  5. #5
    Boolit Master kens's Avatar
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    in muzzleloading round balls, we know that it is more important for the base to be perfect rather the nose.
    I dont know why. But we know if the base is chewed up they wont group. But if the nose is chewed, it dont matter as much.
    That is why we load with the sprue on top.
    No doubt a similar thing exists with bullets.
    I would imagine that a skewed base would have uneven gasses exiting the muzzle

  6. #6
    Boolit Master
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    it's all an educated guess,,,, till the trigger is pulled.

    this opinion brought to you by mister low-tech solution..

  7. #7
    Boolit Master JBinMN's Avatar
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    Thanks for that link.


    Good read!
    "If ya don't like my gate, ya don't have to swing on the hinges..." - L. Ackerman ( RIP)

  8. #8
    Boolit Master
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    Good crown and good bullet base are very important for accuracy. Irregular gas escape at the point of bullet departure from the muzzle will induce a yaw in the bullet flight and adversely affect accuracy. Recut your crown if there are dings or worn sides and cast good boolits. The two work in tandem towards good accuracy.

  9. #9
    Boolit Master OS OK's Avatar
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    Yeah boy...thanks R5R...you the man today!

    That link just lead me to a 4 Volume set of books by F W Mann...'The Bullet's Flight' . . . "Whooopti Do!' . . .
    a m e r i c a n p r a v d a

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  10. #10
    Boolit Master
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    you'll love those books Charlie.

    the original poster of that thread was a PHD type DR. of physics and mathematics
    he unfortunately left us when someone here wouldn't get over some spin rate theory and nagged him to death about it.
    which really sucks because he was working on some rotational stress numbers for me.
    it's all an educated guess,,,, till the trigger is pulled.

    this opinion brought to you by mister low-tech solution..

  11. #11
    Boolit Master OS OK's Avatar
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    Love those technical books...my wife just looks at me and shakes her head!
    a m e r i c a n p r a v d a

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  12. #12
    Boolit Master
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    Quote Originally Posted by kens View Post
    in muzzleloading round balls, we know that it is more important for the base to be perfect rather the nose.
    I dont know why. But we know if the base is chewed up they wont group. But if the nose is chewed, it dont matter as much.
    That is why we load with the sprue on top.
    No doubt a similar thing exists with bullets.
    I would imagine that a skewed base would have uneven gasses exiting the muzzle
    When the bullet exits the barrel is what i was thinking. If one side exits even a small amount before the other the gasses will push the bullet to the opposite side and set up a large yaw. Even nicks in the edge should do the same thing just to a possible less degree. None of it is good for accuracy.

  13. #13
    Boolit Master OS OK's Avatar
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    There could be as much as 6,000 PSI exiting the muzzle right behind the boolit...that's quite a kick in the butt !
    a m e r i c a n p r a v d a

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    “In a time of deceit, telling the truth is a revolutionary act.” G. Orwell

  14. #14
    Boolit Master popper's Avatar
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    Several years ago I purposely nicked the base of several 40SW and got a circular pattern on the target. Recently I shot some 145 gr PB in BO @ 2100 fps. Got the similar 'ring' on the target (100 yds, posted elsewhere). It's an AR so the port cut the base. Proof was a clogged gas key. Barrel has a good crown. GC jacket loads don't have the problem. My solution to not finding inexpensive nose pour moulds is a base that has a very short GC shank and bevels up to the drive band. Effectively the crown 'sees' a nice crisp beveled edge. It also seats straight quite easily. Works in 30/30 & 308 marlin run pretty hard. 308MX 1875 fps, 50 yds. 150gr PB WW + Cu.
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  15. #15
    Boolit Master
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    Quote Originally Posted by ascast View Post
    I am not sure what you mean by "reverse of crown" but bullits have bevel base, boat tail, and nose pour and adding a few wads to improve accuracy.
    If a crown is dented or not cut square with the axis, it allow some of the gases to come out near the dent before the gas on the other side. Depending on the size and shape of the dent the high pressure gas will cause to bullet flight to be off from the bore axis. Recently had a barrel that when bore sighted, bullet would hit 8-10 ft to right of point of aim. Only thing we could find is crown was not cut square with bore axis. I have been applying gas checks using a homemade system which results in the slightly rounded corners of gas checks to be swagged to a very sharp 90 degree angle. I was wondering if this hurt or helped accuracy. I believe it helps.

  16. #16
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    Quote Originally Posted by runfiverun View Post
    you'll love those books Charlie.

    the original poster of that thread was a PHD type DR. of physics and mathematics
    he unfortunately left us when someone here wouldn't get over some spin rate theory and nagged him to death about it.
    which really sucks because he was working on some rotational stress numbers for me.
    The doctor, for all his self claimed ballistic knowledge, had very little understanding of ballistics not withstanding his pontifications of such knowledge. In the reference thread you listed in post #6 the doctor's lack of ballistic knowledge is self evident.

    He begins with the title of his thread;

    Cast bullet Accuracy and Trailing Edge Failure

    The doctor then states;

    "So I had a thought... Probably not a new one, but I haven't yet come across it exactly....... You would think since immediately prior to departure from the bore the base edge of a bullet is confining the gas pressure and restraining inertial wobble that a major impact to accuracy would be the beginning of blow out of this trailing edge due to gas pressure (+ other forces), and subsequent net off axis forces imparted to the bullet. Asymmetric venting during departure would impart forces, and further erosion/scarring could additionally influence the creation of net off-axis forces. Non uniform release of inertial forces could also tend to throw the shot."

    Now with all the doctor's self claimed PHD ballistic knowledge you have to ask yourself.....why doesn't he already know the answer to his question? Could be he's asking a rhetorical question but the next two posts belie the truth;

    When asked; “Have you ever heard of Dr. Mann's the flight of the bullet”

    The doctor answer's with; "Was he the fellow who categorized types of imperfections vs. accuracy impact? Wrinkled, nose defects, base defects, etc? If so, I'm familiar with the experiment generalities but never came across the actual article....”

    His own answer defines his own knowledge of ballistics. Anyone who has studied ballistics and claims to have a PHD in such studies is well aware of Dr. Mann's book and work. Obviously the doctor (DrB to be exact) was not as knowledgeable as he claimed. He was not "nagged" either. He was presented with facts concerning the adverse effect too much RPM can have on bullets and, not having the knowledge he claimed, could not refute those facts with ballistic evidence. Not sure why he left this forum but I'm sure being totally discredited by his own doing may have had something to do with it.

    Now, if you would care to present actual ballistic evidence (facts) that discredits the "spin rate theory" we would all certainly like to see them? Probably a good thing never gave you the "rotational stress numbers" because they probably would have been wrong given his actual ballistic knowledge. The fact that he did not give you the numbers, after saying he would, probably speaks as well to his integrity.

    BTW, another quote I like; "I don't have a PHD.....I have a DD 214......"



    Last edited by Larry Gibson; 11-12-2017 at 07:57 PM.
    Larry Gibson

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  17. #17
    Boolit Master Oklahoma Rebel's Avatar
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    sounds a bit judgemental to me, but I don't know the whole story....interesting stuff either way. I imagine the base of the boolit and the crown have equal consequences, but a marred or otherwise imperfect boolit base only lasts one shot, whereas a bad crown, well, can cause a major toothache!!!
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  18. #18
    Boolit Master


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    Quote Originally Posted by Oklahoma Rebel View Post
    ....... I imagine the base of the boolit and the crown have equal consequences, but a marred or otherwise imperfect boolit base only lasts one shot, whereas a bad crown, well, can cause a major toothache!!!
    Oklahoma Rebel

    That certainly agrees with what I've found but some recent testing appears to demonstrate that a crown not square to the bore isn't as detrimental to accuracy as we think. It also agrees with most "experts" and ballisticians opinions. I've not done a test my self but know that I've corrected a lot of "accuracy" problems over the years with a simple recrowning of the muzzle. Perhaps there are more factors at play here than we think or are considering?
    Larry Gibson

    “Deficient observation is merely a form of ignorance and responsible for the many morbid notions and foolish ideas prevailing.”
    ― Nikola Tesla

  19. #19
    Boolit Master vzerone's Avatar
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    Quote Originally Posted by Oklahoma Rebel View Post
    sounds a bit judgemental to me, but I don't know the whole story....interesting stuff either way. I imagine the base of the boolit and the crown have equal consequences, but a marred or otherwise imperfect boolit base only lasts one shot, whereas a bad crown, well, can cause a major toothache!!!
    I think that too Oklahoma Rebel. Far as I can see it looks like Larry Gibson has broken some forum rules. "Inflammatory Without Merit", "Insulting Other Member(s)" and "Condescending\Arrogant".

    What are your credentials in external ballistics Larry? Don't tell me a DD 214 because that's not going to cut it. My God, Dr B has been gone long ago, and contrary to what you say you did nag him till he could no longer stand you and left, and yet you're still berating him and his education. I've spent hours and hours reading and going over all the old threads and nobody with credentials have agreed with you. Your theory isn't proven. I know from reading here other people have exceeded your threshold and then you came back said you can push it. Then why is it a threshold if you can push it? Definition of threshold:
    the magnitude or intensity that must be exceeded for a certain reaction, phenomenon, result, or condition to occur or be manifested.
    "nothing happens until the signal passes the threshold" Your threshold seems that you can maneuver it to be what you want it to be.
    Last edited by vzerone; 11-13-2017 at 12:57 AM.

  20. #20
    Boolit Master
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    This 'perfect crown' thing has been around a long time. Many experiments have shown that an imperfect crown has little to do with group size. Point of impact can be affected but group size has little change. If you burr or gouge the muzzle, a few shots might go wild due to burrs, but then groups will return. A worn muzzle due to improper cleaning, mostly old military rifles can affect grouping.
    NOW perfect bullet bases are critical, back to Dr. Mann's experiments, the defective bullet base causes lots of trouble. How far you shoot comes into play. Crown angle, another boogey man, square, the magical 11 degrees, 45 degrees, 60 degrees, or rounded? IT really doesn't matter. The barrel Maker, Mr Obermeyer uses 60 degrees because that is what he has from the center used when turning or threading a barrel. He also cleans from the muzzle to reduce the possible damage to the throat, easier to shorten and remove muzzle damage than rethread and chamber. ALL these sacred cows, still alive from BEFORE the internet.

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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