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Thread: Cast bullet accuracy and trailing edge failure

  1. #181
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    Bullshop's Avatar
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    Mar 2005
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    A slower longer push (slow powder burn) seems to be more forgiving than a fast kick in the but (fast powder burn) especially as peak pressures pass about 50% of max and go up from there even of peak pressures of both powder types are roughly equal. This too then would lend credence to the torque issue I was speaking of. Give the wrench a quick hard smack and the lead bolt might break. Apply pressure slowly and maybe it turns.

  2. #182
    Boolit Master
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    I was getting a lot of trailing edge failures from air pockets in the base. Turned out to be my pot was pouring too fast into the mold, frothing the lead up. Slowed down the pour rate and held the mold closer to the nozzle and no more air bubbles.

  3. #183
    Boolit Bub natty bumpo's Avatar
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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
    Very glad to have found this post as I have Just now begun doing just what you suggest which is examining recovered rounds. Not not claiming anything to be true but only what I have observered and surmised by these observations. The first observation is that the entire base of the bullets that I found is almost clean with little or no deformity save for a relatively small area that is craters from the burning powder. This area is almost always off center as it is a random event and does not encompase the entire surface of the base but only shows a small impact zone. It seems that the further from center that this cratered area is the more apt that the bullet is going to show signs of tumbling through the flight path as evidenced by the impact damage on the bullet. Some of these boolits show quite clearly that the boolit impacted on it's side Perpendicular to the normal axis of the intended direction.

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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