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Thread: Cast bullet accuracy and trailing edge failure

  1. #141
    Boolit Grand Master popper's Avatar
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    Thanks. I've notices a marked increase in accuracy between H4895(short stick) and Lever powder( small ball) in 30-30, wondered if peening is the problem. Ran some RD 311 170 PB butt first through the sizer. I'll shoot them and see if there is a difference. Bases have a sharp edge, not frilly like running them nose first. I shoot at a commercial range and have no way of recovering bullets.
    Last edited by popper; 02-23-2012 at 02:54 PM.

  2. #142
    Boolit Buddy

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    Have to get around to it someday...

  3. #143
    Boolit Grand Master JIMinPHX's Avatar
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    Quote Originally Posted by Shome10x View Post
    Stupid question....

    How does the "pressure" differ between a fast or slow powder? If the velocity is the same, how would this affect flight?

    Reason I ask, the same bullet can fly extremely well whether "pushed" by Bullseye or Unique. Help me understand the logic...

    Thanks,

    Chris in MO
    I did some experiments a few years ago with a .44 mag & found that a fast powder would deform the boolit more than a slow powder. I fired two loads with the same muzzle velocity into crumb rubber & recovered the boolits. The ones that were pushed by H110 were hardly deformed at all. The ones pushed by Unique were deformed noticeably. I don't know if I still have the pictures or not.

    Edit:
    This may be of interest - http://castboolits.gunloads.com/show...8-BNH-Vs-Speed
    Post #54 on page 3 shows the different deformation with different powders.
    Last edited by JIMinPHX; 01-24-2013 at 02:07 AM.
    “an armed society is a polite society.”
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  4. #144
    Boolit Grand Master popper's Avatar
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    JIm - after reading the delirious rants of all 5 pages of that thread BNH-Vs-Speed, I conclude that your original alloy was too weak (toughness, not hardness) for the pressure, the CBs were too small as evidenced by the lead coating on the GCs and that powder kernels at HV do peen the BC base. Note also that at the same pressure, the force on the base of a larger cal is greater, thus possibly greater base damage. The pics of recovered CBs is of value to those of use with limited casting and shooting experience.

  5. #145
    Boolit Grand Master JIMinPHX's Avatar
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    Popper, please help me understand a few things.

    1) why do you say that the toughness of the alloy is the problem & not the hardness? Also, how would you make the alloy tougher?

    2) Why do you say that lead on the GC means that the boolits were undersized? That doesn't make intuitive sense to me. I expect that I am missing something.

    I agree about powder kernels peening the boolit bases. On another thread somewhere, I had posted pictures of boolit bases from 150-gr SWCs that had been fired from a .357 mag with different powders. Some of the bases looked pretty clean, while others were very pock marked. I don't recall which were which.
    “an armed society is a polite society.”
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    "Idque apud imperitos humanitas vocabatur, cum pars servitutis esset."
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  6. #146
    Boolit Grand Master JIMinPHX's Avatar
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    I couldn't find the original thread, but I did manage to find the boolit base picture in my forum archives. If anyone knows how to search for a picture in a thread by the name of the picture, please let me know.

    Thanks,
    Jim

    “an armed society is a polite society.”
    Robert A. Heinlein

    "Idque apud imperitos humanitas vocabatur, cum pars servitutis esset."
    Publius Tacitus

  7. #147
    Boolit Grand Master popper's Avatar
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    Hardness (BHN) and toughness -not breaking apart are related but not exactly the same. Your first pics showed rifling skidding, as you changed the alloy(more WW) it got better. You could also add sulfur or copper for strength but not the brittleness of more antimony. Your pic also had lead smeared over the GC. If the GC & CB are sized properly, there is no space between the GC wall and the bbl for lead to collect. 303guy's pics of deformed bases was informative to me. I was surprised to see pics of unique also damaging the base, as it's small and soft. Nonburning powder gets thrown against the base at high speed and I can see the hard stick stuff peening. My post was kind of a gripe about 5 pages that were pretty much argument and didn't really answer much or provide info.

  8. #148
    Boolit Master detox's Avatar
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    Sorry, but a read very little of this tread, I just thought a would ask this question. Do fiberwads protect against base deformation and cushion bullet when fired. Seems these are the best thing to use with flat based bullets. I want to try some in my .357

  9. #149
    Boolit Grand Master 303Guy's Avatar
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    I've found polyester to protect boolit bases. I used about double the recommended amount but that was over a fairly full case of powder.
    Rest In Peace My Son (01/06/1986 - 14/01/2014)

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  10. #150
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    I have been experimenting by using my swage dies to alter cast bullets. Specifically, I've been changing nose shape and making the bases hollow (hollowpoint punch) and a semi-boattail shape by reversing the bullet in my 3/4 E point former so the trailing edge isn't really contacting the lands much, only a bearing surface between the base and the roundnose point contact the lands. This bearing surface is .4525 in diameter. They shoot very well with minimal leading in testing, so far. They also are a joy to reload. Recovered bullets show no damage to the bases. My groups are 31/2 to 4 " at 25 yards with a Taurus PT1911 in 45ACP, using a sandbag rest. I used 6.1 gr. of Auto Comp, CCI 300 primers and mixed brass. The trailing edge of your typical cast bullet may have less effect than we think. This design allows excellent allignment in the case, no size reduction from taper crimping and sufficient contact with the lands to provide accuracy.

  11. #151
    Boolit Grand Master 303Guy's Avatar
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    This design allows excellent alignment in the case, no size reduction from taper crimping and sufficient contact with the lands to provide accuracy.
    Any chance of a photo? I'm thinking of reducing the base of my boolits to prevent the rifling lands from squeezing those little bumps into the base. In effect, a bore-ride boolit base, but very short and with a taper step down so that the step itself doesn't form irregularities from the rifling.
    Rest In Peace My Son (01/06/1986 - 14/01/2014)

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

  12. #152
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    Quote Originally Posted by DrB View Post
    So I had a thought... Probably not a new one, but I haven't yet come across it exactly. I'd appreciate the feedback of the more experienced/observant cast bullet shooters out there. "Papa smurf" had a related thought so I know others are thinking along the same general lines.

    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.

    Trailing edge failure could explain a lot of the correlation between bullet hardness (and gas checking) and better accuracy at higher velocities (and higher muzzle pressure). 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.

    It would be neat to examine bases of plain base lead bullets below and well above the velocity where accuracy had significantly degraded, if you could recover them without much impact damage and look for gas erosion/scarring/fracture of the base surface, and particularly imperfections of the base edge where it departs the muzzle.

    Any thoughts, observations, references to prior discussion of same?

    Anyone ever shot a uniformly soft lead bullet vs. one with just the very base quench hardened? Or how about a gas check that was just a crimped on ring (a cup with no bottom, but a perfectly flat bottom edge) extending just past the base of the lead bullet?

    Best regards,
    DrB
    The bullet as it leaves the muzzle is affected by not only the base (use a wad or GC in my opinion) but also the muzzle itself. A nick on the crown can ruin a bullets path in my experience.. which until you learn of it may be forever frustrated till someone with a more trained eye discovers your potential... but it is an extremely easy fix. That's one... poor casting... especially with hollow bases... poor pours... all have caused me huge accuracy problems... gas checks and wads.... (in my opinion.) I'm using as pure a lead as i can...

  13. #153
    Boolit Master
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    Quote Originally Posted by detox View Post
    Sorry, but a read very little of this tread, I just thought a would ask this question. Do fiberwads protect against base deformation and cushion bullet when fired. Seems these are the best thing to use with flat based bullets. I want to try some in my .357
    I use walters wads with my heaviest loads or gas checks... walters wads are great as are some other homemade concoctions I've shot. These are in muzzleloaders with the softest lead I can find.

  14. #154
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    I used to have rounded base problems. I tried running the mold colder than the alloy, having a thermometer in the lead pot,, using a bit more antimony, etc, and those tips helped. But what REALLY fixed the problem was using a spout-pour ladle, instead of the open dipper supplied by Hensley and Gibbs.

  15. #155
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    It is a shame that Lee quit making their pistol rest. With good ammo, guys, a good 1911 groups 2" and less at 50 yds, for 5 shots. Not 3" at 25 yds. I had one wonderful variant, which was an Old NM slide group, on an Essex frame, back in 1970, which really would (from the Machine rest) group into 9" at 200 yds. This was with Remington jacketed swc match ammo, 185 grs at about 750 fps. When I looked thru the sights, they were aimed over 20 ft above the target! A friend had to go downrange about 150 yds, to the side and behind a big tree, and call out my hits, until I got on target. I recall a mag article of a guy doing the same, IIRC, it was with hot jhp loads, in a 38/45 version of the 1911. the guy wanted to do well in 200 yd metallic silouette shooting, using a 1911, but the retained momentum was not high enough to knock over the rams.

  16. #156
    Boolit Master
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    One reason base defects are more deleterious that nose defects is that they are farther from the axis of the bullet. The farther an imbalance is from the axis of a rotating object the greater the imbalance.

  17. #157
    Boolit Grand Master popper's Avatar
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    Glue a string to the nose and pull it around. CB follows the string pretty good. Now push it around with a pencil point on the base. Not so good?
    Whatever!

  18. #158
    Boolit Grand Master 303Guy's Avatar
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    Good analogy. That applies to muzzle blast. I'm not sure how trailing edge damage effects a stable boolit in flight, after all, there is a shock wave propagating off the trailing edge so perhaps the trailing edge gets tugged in a spiral with the same pitch as the boolit spin. This might accentuate as the boolit travels down range rather than dampen as a muzzle blast tipping would. On the other hand, perhaps the muzzle blast tipping is made worse by the unequal trailing edge.

    Consider also that some boolit designs are less stable than others. A flat nose boolit is less stable than a round nose of the same length (not weight) and a spire point is more stable still (unless it suffers nose slumping in the bore). A spire (or spitzer) point will likely dampen any yaw and related spiral flight path while a flat nose might increase the yaw and spiral boolit path (not sure on that!) This is of course speculation. I'm getting my information from; http://www.border-barrels.com/barrel_twist.htm. Check it out for yourselves and you can see how nose shape affects stability. It shows required spin but is a bit confusing as it looks like it's upside down. You'll see what I mean.

    Now playing around with the twist calculator one will find that small changes to the boolit base (the boat tail) causes large changes to stability for small changes while changing the nose shape has a smaller effect (and surprisingly, some shapes are more stable in the transonic zone!? Bear in mind it's a software simulation - the algorithm may be inadequate in that zone).
    Last edited by 303Guy; 08-06-2013 at 06:02 PM.
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  19. #159
    Boolit Mold Westerner's Avatar
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    This thread has been on for a long time. I shoot 45/70 in a Sharps action with 30-1 Lead/tin mix. It took a plastic card wad between a smooth card wad and perfect base of a 500 grain round nose lubed bullet to print less than 1.5" at 100 yards. The slug comes from a nose pour mold that is held closed for 3 minutes before it is dropped into water in a shallow pan with a cushion at the bottom. Each slug is put into a shallow reloading tray nose down between casts. Nothing touches the bottom of the bullet until it is pushed into a slightly belled case mouth on to the two wads and powder charge and taper crimped. Roll crimps scrape the bullet shaft so avoid that step.

  20. #160
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    The formula for predicting torsional stress imparted to the engraved bullet by the rifling is as follows:

    F/A = .00000697 · ((WrV²) / (Pldn))

    Where

    F=total force in pounds exerted upon the bullets by the leading sides of the lands.
    A=total area in square inches of the leading sides of all the lands taken by the bullet.
    F/A=force per square inch upon the leading sides of the lands.
    W=weight of bullet in grains.
    V assumed to be equal to the muzzle velocity of the bullet by which the above formula becomes empirical.
    P=pitch of the rifling in inches.
    n=number of grooves in the rifle bore.
    r=radius of bullet in inches.
    L=length of bullet which takes the grooves (bearing surface) in inches.
    d=depth of rifling grooves in inches.

    This is taken from F. W. Mann's book The Bullet's Flight.


    Gear

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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