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Thread: Measuring bore diameter

  1. #1
    Boolit Bub
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    Measuring bore diameter

    Is there a way to measure bore diameter without buying a bore gauge?

  2. #2
    Boolit Master TurnipEaterDown's Avatar
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    Even number of grooves: pound a lead slug (slightly oversize ball works) through a lightly lubed bore.
    Odd number of grooves: more difficult.

  3. #3
    Boolit Master
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    Lube your bore and slug before driving the slug into the bore

  4. #4
    Boolit Master
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    It appears you are describing land diameter ( bore diameter) as opposed to groove diameter. The correct way is with pin gages. It is possible to use a bore rider boolit if the land markings are visible on the bore riding surface. The very beginning of the land engraving should be very close to land diameter. The boolit can be inserted in the muzzle and either twisted lightly to mark the tapered bore riding portion or tapped into the muzzle enough to lightly engrave the boolit.
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  5. #5
    Boolit Master Castaway's Avatar
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    Last edited by Castaway; 11-28-2023 at 03:57 PM.

  6. #6
    Boolit Bub
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    Thanks everyone. Yes, I am trying to determine land diameter. Never used pin gauges before and would rather not spend the $ for something that will see such little use. I will try to find some bore riders or some kind of tapered lead and see if I can get an impression that I can measure. Also found some small diameter bore gauges on Amazon that may work and they are reasonable.

  7. #7
    Boolit Buddy TomAM's Avatar
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    Your local machine shop has sets of gauges, and for a small fee fight be willing to get you a measurement.

  8. #8
    Boolit Buddy steveu's Avatar
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    Get some cerrosafe and make a cast.

  9. #9
    Boolit Grand Master Good Cheer's Avatar
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    Quote Originally Posted by fayettefatts View Post
    Thanks everyone. Yes, I am trying to determine land diameter. Never used pin gauges before and would rather not spend the $ for something that will see such little use. I will try to find some bore riders or some kind of tapered lead and see if I can get an impression that I can measure. Also found some small diameter bore gauges on Amazon that may work and they are reasonable.
    With the twist test (using the lands to machine down a bullet) do a few of them until you get the feel for what you're doing and make a few to check. Don't just do one and run with it.

  10. #10
    Boolit Master
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    If you’re paper patching for smokeless you need groove diameter not bore.
    I have danced with the Devil. She had excellent attorneys.

  11. #11
    Boolit Bub
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    Quote Originally Posted by Digital Dan View Post
    If you’re paper patching for smokeless you need groove diameter not bore.
    I've been shooting patched to bore paper patched bullets for quite a few years using WC872 & 867 also IMR 3031. Patched bullet is .100 into the case and lightly taper crimped. Accuracy is just as good as my BP loads.

  12. #12
    Boolit Grand Master Nobade's Avatar
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    I'm surprised that works. What cartridge? I've been able to bump bullets with Blackhorn 209 but not with any other smokeless powder.

    In my experience I don't really care what the groove diameter is, I want to know what the throat diameter is. I size the bullets so they fill the throat, trying for no more than .001" under the throat size. I want that thing to plug the hole as fast as possible before the gas has a chance to blow past it and ruin everything.

  13. #13
    Boolit Bub
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    Quote Originally Posted by Nobade View Post
    I'm surprised that works. What cartridge? I've been able to bump bullets with Blackhorn 209 but not with any other smokeless powder.

    In my experience I don't really care what the groove diameter is, I want to know what the throat diameter is. I size the bullets so they fill the throat, trying for no more than .001" under the throat size. I want that thing to plug the hole as fast as possible before the gas has a chance to blow past it and ruin everything.
    I've been using this for 45-90,45-70 38-70,38-55. I run a .443 slick patched to .450-.451 in the 70 and 90.My Sharps has a tighter bore than my HighWall and uses a thinner paper for a slight interference fit.I'm also using wheelweights for all my bullets and size the dry patched bullets in an NOE push thru sizer using my own custom size bushings. FWIW.Mike

  14. #14
    Boolit Grand Master Nobade's Avatar
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    I gotta try that again in my Ruger #1 with the dedicated paper patch chamber.

  15. #15
    Boolit Bub
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    I used to use a 3 wad stack in the 90 to take up excess space in the case,now I use a combo of floral foam and a .060 LPDE wad compressed .10. That's how much bullet is in the case. Primers seem to make the biggest impact on SD's and ES's. Aprimer change can make a 100fps difference.FWIW. Mike.

  16. #16
    Boolit Grand Master Nobade's Avatar
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    Are you duplex loading those slow powders or using them straight? Sounds like otherwise you're loading them just like you would with black powder?

  17. #17
    Boolit Bub
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    Quote Originally Posted by Nobade View Post
    Are you duplex loading those slow powders or using them straight? Sounds like otherwise you're loading them just like you would with black powder?
    I started out duplexing with RL-7 when I was using greasers now with paper patching I load them without since there's a lot more case capacity especially with the 90.Other than that you pretty much load just like BP,powder,wad,compression die,seat,and slight taper crimp.FWIW Mike.

  18. #18
    Boolit Grand Master Nobade's Avatar
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    Thanks, I'll let you know what happens.

  19. #19
    Boolit Master
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    Back in the 1950's, GONRA didit for my 6.5x50.5mm Japanese rifle
    by macihning a slip-fit bore plug ,
    then crossdrilling 1/16 for "groove rider pin" that
    (once fitted) determined groove diameter.

  20. #20
    Boolit Master

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    Amazon has a 250-piece, .251" to 0.500, 0.001" increment pin gauge set for $136 that will handle anything gun-barrel-related except the very large and the very small.

    If you're into this casting thing to any real degree, ESPECIALLY with revolvers, consider it a cheap answer to a real need.
    WWJMBD?

    In the Land of Oz, we cast with wheel weight and 2% Tin, Man.

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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