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Thread: DDPP bullet finning

  1. #1
    Boolit Buddy
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    Oct 2015
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    DDPP bullet finning

    Hi,
    Last year with help from fellows including Arnie, I designed a DDPP bullet for my Browning BPCR, .45-70. It was designed to be patched with BACO .0020” paper and the belted portion to be a slip fit in a fired unsized case. Brooks made the mold and it was very close, within a thousandths, of the print and the bullet drops easy from the mold. Alloy is 16:1, 83gns Swiss 1 1/2 , .065 LDPE wad, and patched to the base. BACO paper is used and the bullet is a very light slip fit in the case. Seating depth is .075” . You can carefully lift the case up by the bullet but a little shake and the case will drop away. Accuracy is sub MOA at 100 yards and opens up to 1.7 MOA at 200. Not what I would call great but not bad.
    Below are photos of the bullet along with the bullet dimensions along with the wrapped dimensions. The bore of the rifle is spot on at .450” measured by slugging at the breech end. Star brass and wall thickness at neck is .0095”. The bullet marked with a W was patched Hyde style and you can see the imprint of the folded patch in the bullet base. Both bullets fired into my swimming pool. They show a lot of base deformation, how much this affects accuracy is a guess but it can’t help. With the thin paper the base diameter is still over groove diameter by .0012” but the bore diameter size is so small I can about hear the bullet rattling down the barrel...the accuracy is minute of barn door. Loading was fiddle with this thin paper as the bullet was loose in the case.
    Thoughts?
    Cheers Richard

    Click image for larger version. 

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    Last edited by flatsguide; 09-08-2021 at 08:14 PM.

  2. #2
    Boolit Grand Master Don McDowell's Avatar
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    Well that's the thing about paper patch bullets, there's no place for the alloy displaced by the rifling to go except over the edge of the base. So if the bullet is over bore diameter to start with then you add the paper thickness, you'll end up with what your pictures show.
    Grease groove bullets have that problem if they get to far over groove diameter, altho a lot if it is absorbed by the lube grooves.
    You may want to try a thinner paper something in the 7 lb territory to see if that finning and base cupping subside a little.
    Long range rules, the rest drool.

  3. #3
    Boolit Buddy
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    That’s the problem Don, there needs to be a match in bullet diameters, as I mentioned using thinner paper will work for the belt section then the bore section of the bullet winds up too small in diameter. Not much one can do except design a DDPP around a particular paper, preferably thin, so both bullet diameters patch to optimum size, say .451” for the bore and .458” for the belt then neck the case down to fit the belt section.
    Cheers
    ,

  4. #4
    Boolit Grand Master Don McDowell's Avatar
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    From what my rifles have told me over the years, any time the bullet before wrapping gets bigger than the bore, the more fits it will deal you.
    The two 45 caliber dual diameter bullets I shoot both are .450 on the base, and something around .454 after wrapping, both wrapped in SC 55Y. One of them shoots very well in all but one rifle, the other I'm just been running a bit this summer, and it shoots well enough out to 600 or so, and not bad but not great beyond that, and I'm thinking that's because it's just a tad long for the 18 twist. I haven't tried it in the 16 twist gun as that one is a pretty tight bore, and has a real hissy fit when the bullets get to large.
    Both of the dual diameters work in the Browning bpcr, but the newest one doesn't shoot quite as well. I'm thinking shorten the bullet up to 1.43 and it may come in like gang busters. It will shoot 3 inch groups at 300.
    I am starting to think all things considered it gets pretty tough to beat a straight sided bullet from .444 to .446 before patching, as long as the bullet length doesn't crowd what the twist will handle.
    Long range rules, the rest drool.

  5. #5
    Boolit Buddy
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    A couple of thoughts come to mind.
    It is noted that the bullets must have bumped up, seeing that the heretofore .450" patch to bore body is deeply engraved by
    the rifling. And, of course the "greater than bore diameter" 0.4552 base band is deeply engraved.
    -- Try sizing the base band down to perhaps 0.452-0.453"(a convenient "45 auto" sizing die size)-probably need to go to a slight taper crimp then.

    --Consider going to an alloy that will reduce bump up.

    And, of course stay with the thicker paper that gives you a good slip fit of the "patch to bore" body of the bullet.
    beltfed/arnie

  6. #6
    Boolit Buddy
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    Hi Arnie, thanks for weighing in. I’ll try your suggestion of reducing the belt dia although I was hoping initially to not have to neck the case. I’m heading in the direction to reduce anything that causes the bullet base to be deformed.By swaging the bullet down I’ll try base first then nose first and see were the excess lead goes. I have come to the understanding that any base deformities are very detrimental to good accuracy.
    Thanks Richard

  7. #7
    Boolit Mold
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    Just a thought try it with harder alloy and see what happens. nothing too lose, moezingo

  8. #8
    Boolit Buddy
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    I order my lead alloy,16:1, from Roto metals or BACO, I’m wondering now if I may have gotten a softer alloy. It sure has a lot of engraving for supposedly 16:1 I’ll break out my hardness tester and see wazzup.
    Thanks for jogging the little grey cells, as someone used to say.
    Thanks Richard

  9. #9
    Boolit Grand Master Don McDowell's Avatar
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    What do the fired bullets measure?
    Long range rules, the rest drool.

  10. #10
    Boolit Buddy
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    Click image for larger version. 

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  11. #11
    Boolit Buddy
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    Tried to rotate the info you wanted Don but no luck.
    Cheers Richard

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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