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Thread: Why is long bullet jump to the forcing cone a bad thing?

  1. #1
    Boolit Buddy
    Join Date
    Aug 2012
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    EP Texas
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    Why is long bullet jump to the forcing cone a bad thing?

    The gun in question is a Ruger Blackhawk 45/45ACP convertible. Both cylinders were .450 so I bought the reamer and pilots and they are both now at a perfect .451. Until this is done neither cylinder shot lead well and of course the barrel leaded.

    So the reason for the question is many people claim their Blackhawk shoots badly with the 45ACP cylinder due to the long bullet jump to the forcing cone. With my gun the most accurate load is 45ACP with virtually any 200 Gr, LSWC with almost any published load data. I have even used the same bullet in 45 Colt brass and taper crimped with a 45 ACP die and while it shoots well it still will not match the 45 ACP cylinder.
    So, based on my experience (With one gun) I don't think the bullet jump is a concern.
    Don't get me wrong, the 45 Colt cylinder shoots very well, its just that with the ACP cylinder the thing is a real tack driver.

    I would be interested in any technical reasons this bullet jump is a bad thing.

    Thanks
    Mike

  2. #2
    Boolit Man
    Join Date
    May 2017
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    Round Rock, TX
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    Longer jump generally equates to more opportunity for misalignment. In this scenario the boolit is well supported and aligned during acceleration. Smith 625's in .45acp generally have a reputation for accuracy despite the same long jump though the cylinder throats. Unsupported boolits in the throat can misalign during launch, more commonly seen with a nose profile that is loose in a rifle chamber with generous dinensions where the case neck is hanging in the air and no boolit contact ahead of it.

  3. #3
    Boolit Master Outpost75's Avatar
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    A long jump in revolvers only hurts if the cylinder throats are oversized and when bullets don't fit.

    When cylinder throats are groove diameter to +0.0015 over, bullets fit throats and chamber barrel alignment/indexing are correct, gun will shoot.
    Last edited by Outpost75; 10-12-2017 at 04:06 PM.
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  4. #4
    Boolit Master
    runfiverun's Avatar
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    it isn't bad in fact it is generally more accurate.
    see the post above this one.
    it's all an educated guess,,,, till the trigger is pulled.

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

  5. #5
    Boolit Master
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    May 2009
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    North Central Montana; across the wide Missouri
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    My Ruger convertible, 2005 new, was also a terrible shooter. I reamed both cylinders, all 12 chambers to .4525 as I size my casts to .452. The ACP cylinder is the most accurate of the 2 cylinders. I use 200 and 230 gr. bullets in the ACP and 240 to 260 in the Colt cylinder. The idiosyncrasies of the convertibles are a puzzlement

  6. #6
    Boolit Master
    mdi's Avatar
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    FWIW; I experimented with 44 Special brass in my 44 Magnums with bullets seated both "long" and "short". Also tried bullets in Magnum brass seated "long" (way long) and short and in both cases, any difference was too small to tell. I believe bullet fit to the throat and possible misalignment would contribute to the "long jump" problems...
    My Anchor is holding fast!

  7. #7
    Boolit Buddy
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    Thanks for everyone's input, makes sense and is pretty much what I thought based on my experience.
    I can see the rifle scenario being a problem if the bullet doesn't fit the chamber well.

    Mike

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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