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Thread: Precise micrometer measuring technique for cast boolits.

  1. #1
    Boolit Bub
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    Precise micrometer measuring technique for cast boolits.

    I'm starting this thread because I'm having a problem properly measuring my boolits with a micrometer. In a nutshell I believe the micrometer is squeezing the boolits enough to spoof the measurement by half a thou or so.

    Recently I beagled one of my molds and I cast some oversize boolits using 1:20 alloy. As cast they measured 460~462. Then I sent few through a Lee 459 resizing die. Imagine my surprise when they measured exactly 458! I thought that maybe it is grease that causes it. So I degrease the die with acetone. I lubricated the boolits only with s bit of wd40 and I run another one through the die. Again it measures 458.

    Few words about me and my measurements. I have been a hobby machinist for almost a decade. I have various micrometers, calibration gages, a granite surface plate etc and I believe I know how to use them to measure things made of steel, aluminium, bronze etc. However, lead alloys are problematic.

    99% of you that read so far probably thinks my Lee sizing die is undersized. I thought so too. Before I prepared everything to lap it bigger. I measured it with a bore gauge and it turns out it is exactly 459 thou! (maybe a tenth or two under, but no less).

    So I tried to be very careful when measuring my boolits with the micrometer. Instead of turning the knob as usual until the clutch mechanism clicks I set the micrometer to 459 exactly and tried to move the boolits to pass through the measuring faces. I did manage to push it through with a little bit of noticeable drag. However, when set to 458.8 there is no way I can push it through. However if I measure it "normally" it measures 458.0. I also tried moving the boolits gently between measuring faces while moving the micrometer slowly from 459 to 458. It grabs at around 458.6 with enough force so I can't move it any more gently. However the clutch doesn't engage at this stage. The knob can be turned further half thou before it clicks...

    It is quite a bit of a puzzle.

    I was considering measuring it with a dial indicator on a stand on a surface plate (referencing off some gauge blocks), but those dial indicators feel like they apply quite a bit of force too. So that's not going to work to give me any certainty about the dimension.

    Any ideas? What is your way to measure boolits? How do you avoid this problem?

  2. #2
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    matrixcs's Avatar
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    First things first.. If the lee sizing die is carbide it probably needs cleaning. I my experience I have seen undersized bullets caused by buildup on the carbide ring.
    The micrometer issue will depend on the micrometer. Ordinary ones require you to develop a feel for the torque required to make an accurate measurement. Practice using the least torque to get 0 on closing it and that is the correct torque. All measurements will then be accurate.
    Some micrometers have a knurled torque band to assist in achieving correct torque.
    "We hang the petty thieves and appoint the great ones to public office." -- Aesop

  3. #3
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    I replied in your other thread that you may benefit from a pound cast of your chamber and throat to get accurate measurements of what would be your maximum diameter boolit you could use, this would need to come before diving much deeper into what the micrometer says as you may need to shift everything up a thou or more to achieve good fitment in the throat. THEN figure out an acceptable compromise at the mic to make things work for you.

    Some wold suggest using a shim wrapped around the boolit, .001" to start, then subtracting 2x the thickness of the shim from the mic reading, but .001" may be thin enough to allow some compression of the boolit behind the anvil, as you go thicker in shim stock you lessen the possibility of compression but you then add possibility of error by the springy nature of the shim stock to resist hugging the curvature of the boolit.

    If I had to work with what you are working with I think I would roll a narrow length of shim stock around a smaller gage pin until it sprang back just slightly bigger than the boolit you want to measure, I would then cut this with a dremel tool and make a "C" shaped shim just big enough to slide the boolit into and let the mic compress it against the boolit to gain a measurement gaging the amount of friction it takes to keep the boolit from moving with your fingers until I achieved consistency. Then subtract the thicknesses of the shim and you should arrive at a fairly repeatable measurement.
    Last edited by DougGuy; 06-05-2021 at 09:42 AM.
    Got a .22 .30 .32 .357 .38 .40 .41 .44 .45 .480 or .500 S&W cylinder that needs throats honed? 9mm, 10mm/40S&W, 45 ACP pistol barrel that won't "plunk" your handloads? Click this link to send me a PM->>> http://castboolits.gunloads.com/priv...=newpm&u=29606 Also on Facebook: https://www.facebook.com/Cylinderhone-756429174391912/

  4. #4
    Boolit Master Forrest r's Avatar
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    Never hurts to verify that your mic is setup correctly. I use these gauges and wrenches to reset mine every along with checking them once a month.
    [IMG][/IMG]

    I keep square gauges around to use with calipers. When I'm checking oal's on rifle bullets I like to verify the calipers are reading correctly with a square gauge that is as close as I can get to the oal's length.
    [IMG][/IMG]

    Not saying anything is wrong with your mic's. Just doesn't hurt to verify that they are set correctly.

  5. #5
    Boolit Grand Master

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    There are several things to try here.
    1) use a very light touch on the mike. Hold it with thumb and little finger in the frame and just roll the thimble with fore finger. This gives a very fine feel and removes the force of the clutch or ratchet. Make sure mike is zeroed to this feel

    2) dont actual measure but gauge them. Here a small vee block with stop across one end. A dial indicator in a mag base is indicator base stand. set this up on a surface pate or known flat surface. pin gauge off desired dia and zero indicator to it. set bullet in vee block and slide gently under indicator. Any variation is read as +/- from pin on the indicator.

    in #2 being a hobby machinist an simple indicator stand with vee could be made and dedicated to this. A decent indicator and it could be set on any bench and used.
    Materials needed would be a 1/2-1" 6 x 6 plate of steel or aluminum. a short length of 3/4"-1" round stock drill rod is best. a bloack of aluminum width depends on the rod + 1/8" X 2. this is to make the ind mount. Assorted allen head cap screws.

  6. #6
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    Quote Originally Posted by flynth View Post
    I'm starting this thread because I'm having a problem properly measuring my boolits with a micrometer. In a nutshell I believe the micrometer is squeezing the boolits enough to spoof the measurement by half a thou or so.

    Recently I beagled one of my molds and I cast some oversize boolits using 1:20 alloy. As cast they measured 460~462. Then I sent few through a Lee 459 resizing die. Imagine my surprise when they measured exactly 458! I thought that maybe it is grease that causes it. So I degrease the die with acetone. I lubricated the boolits only with s bit of wd40 and I run another one through the die. Again it measures 458.

    Few words about me and my measurements. I have been a hobby machinist for almost a decade. I have various micrometers, calibration gages, a granite surface plate etc and I believe I know how to use them to measure things made of steel, aluminium, bronze etc. However, lead alloys are problematic.

    99% of you that read so far probably thinks my Lee sizing die is undersized. I thought so too. Before I prepared everything to lap it bigger. I measured it with a bore gauge and it turns out it is exactly 459 thou! (maybe a tenth or two under, but no less).

    So I tried to be very careful when measuring my boolits with the micrometer. Instead of turning the knob as usual until the clutch mechanism clicks I set the micrometer to 459 exactly and tried to move the boolits to pass through the measuring faces. I did manage to push it through with a little bit of noticeable drag. However, when set to 458.8 there is no way I can push it through. However if I measure it "normally" it measures 458.0. I also tried moving the boolits gently between measuring faces while moving the micrometer slowly from 459 to 458. It grabs at around 458.6 with enough force so I can't move it any more gently. However the clutch doesn't engage at this stage. The knob can be turned further half thou before it clicks...

    It is quite a bit of a puzzle.

    I was considering measuring it with a dial indicator on a stand on a surface plate (referencing off some gauge blocks), but those dial indicators feel like they apply quite a bit of force too. So that's not going to work to give me any certainty about the dimension.

    Any ideas? What is your way to measure boolits? How do you avoid this problem?
    Just like matrixcs suggested, "Practice using the least torque to get 0 on closing it and that is the correct torque. All measurements will then be accurate."

    I know if I twist the Mic like I'm playing foosball, I get much smaller readings on lead boolits, LOL
    ~~~~~~~~~~~~~~
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  7. #7
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    All my mics have the "clicky" torque mechanism ( a purely technical term!!! ) in them to allow repeatable measurements from item to item and person to person. Same torque every time....repeatably

  8. #8
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    It may also depend on the quality and age of the mics in question. I have a new set of HF mics that are pretty tight, and a B&S from machine shop Vo-Tech that is getting a bit loose. Is there any way to tighten up a loose micrometer?
    Lead Forever!


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  9. #9
    Boolit Buddy
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    I've recently started a thread about similar issue with Lee bushing sizers. I've also contacted Lee and had been told it is "as designed". None of my bushings accepts -0.0002 pin of stated diameter. CS from Lee told me that they do it on purpose in anticipation of "spring back". Basically your .459 die guarantees that bullet going to be "no more than" 0.459 (from 0.458 to 0.459).

  10. #10
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    Quote Originally Posted by bangerjim View Post
    All my mics have the "clicky" torque mechanism ( a purely technical term!!! ) in them to allow repeatable measurements from item to item and person to person. Same torque every time....repeatably
    I agree!

    I prefer the ones with the slipping clutch instead of the ratchet for measuring boolits. It’s easier to be precise without over torquing. Most good micrometers will include a feature like this. Take a look on the ‘bay, you should be able to find a starrett or Mitutoyo for under $20.

  11. #11
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    Quote Originally Posted by zarrinvz24 View Post
    I agree!

    I prefer the ones with the slipping clutch instead of the ratchet for measuring boolits. It’s easier to be precise without over torquing. Most good micrometers will include a feature like this. Take a look on the ‘bay, you should be able to find a starrett or Mitutoyo for under $20.
    Nope go north another $25
    Got a .22 .30 .32 .357 .38 .40 .41 .44 .45 .480 or .500 S&W cylinder that needs throats honed? 9mm, 10mm/40S&W, 45 ACP pistol barrel that won't "plunk" your handloads? Click this link to send me a PM->>> http://castboolits.gunloads.com/priv...=newpm&u=29606 Also on Facebook: https://www.facebook.com/Cylinderhone-756429174391912/

  12. #12
    country gent has given the right advice. No micrometer should have a clicker or slip end, you will never get the true measurement. I loop my little finger in the mic and hold it in the palm of my hand, then use my forefinger to roll the mic with as little pressure it takes to turn the barrel. When it makes contact, that's it. No more pressure.

  13. #13
    Boolit Bub
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    Quote Originally Posted by DougGuy View Post
    I replied in your other thread that you may benefit from a pound cast of your chamber and throat to get accurate measurements of what would be your maximum diameter boolit
    Thanks. That's always a good advice. I've done that as a first thing when I got this rifle a year ago. I took all the measurements, but I kept the pound cast so I can refer to it in doubt.

    Quote Originally Posted by country gent
    There are several things to try here.
    1) use a very light touch on the mike. Hold it with thumb and little finger in the frame and just roll the thimble with fore finger. This gives a very fine feel and removes the force of the clutch or ratchet. Make sure mike is zeroed to this feel
    and
    Quote Originally Posted by B R Shooter
    country gent has given the right advice. No micrometer should have a clicker or slip end, you will never get the true measurement. I loop my little finger in the mic and hold it in the palm of my hand, then use my forefinger to roll the mic with as little pressure it takes to turn the barrel. When it makes contact, that's it. No more pressure.
    That works, but it relies quite a bit on "the feel" when it touches. After practicing a bit I use this method now for quick measurements at the reloading table.

    Regarding the quality of the micrometer, everyone has their favourite brands. One of my favourites is Limit. It is a Swedish company. Their quality is pretty good at half the cost of Mitutoyo. Also I have lots of stuff made in Poland, Czech, and Russia back in communist times. Buying that stuff (new old stock) I haven't been disappointed with quality yet.
    For example one of my favourite dial indicators (Czech)
    Or dial caliper stand/height gage (Polish)

    Or a Microcator and its stand (Soviet)
    Yes those units are 0.2 of a micrometer so around 7 millionths of an inch

    Coming back to the subject of the thread... in the end to make "certain" measurements I used a medhod similar to one suggested in your replies.Thanks for those. I took a 1.5mm gauge block (60 thou), I put it on the bullet on a surface plate and kind of rolled it under a dial indicator. I previously calibrated it to zero at a known amount plus 1.5mm. So the biggest indication gave me the diameter. This method will only work for non tapered cylinders as I didn't use a vee block. It worked for that bullet design fine.

    As for the Lee die being under size, it definitely was 2~3 tenths under. I opened it up to exactly 459.2.

    Now I'm making my own sizing die to be set to 460 as that is the diameter of a fire formed case. Then I'll test both bullets sized with that 459.2 and my 460 at the range.

  14. #14
    Boolit Master KYCaster's Avatar
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    I'm surprised nobody has mentioned alloy hardness.
    The softer the bullet the smaller it will be when it comes out of the sizing die.
    The softer the bullet the harder it will be to get an accurate measurement.

    Jerry
    Buzzard's luck!! Can't kill nothin', nothin'll die!!

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