Caliper Accuracy Issues

Discussion in 'Ammunition & Reloading' started by Richz99, Feb 20, 2011.

  1. Richz99

    Richz99 New Member

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    Need some help…

    I’ve decided to get into reloading, so I bought a few things yesterday including a dial caliper and a Sierra reloading manual. I’ve been wanting to start reloading for a few years now, and I’m finally taking the plunge.

    So anyway, I’m reviewing some of the data in the manual at the same time I’m measuring some of my ammo here at home, but the numbers don’t match?! My problem is that I’m concerned that my caliper isn’t accurate, but I don’t really have a way to verify without getting a second caliper.

    Here are a few examples: When I measure the bottom (rim?) of the .45 ACP case, I come up with .476”, but the book says it should be .480”. The same holds true when I measure the rim of a .357 magnum case, I measure .434”, but the book says .440”

    Now, if the readings were always consistent (say .005 off), I could conclude that my caliper has issues, but sometimes the reading is spot on. For example, when I measure the bullet for a 7.62x39 cartridge, I get a value of .311, which is exactly what I would expect.

    So what do you folks think? Is this normal, or do I need to replace this caliper? If it’s normal, do the values in the book represent the max allowable?

    Thanks in advance for any help.
     
  2. JonM

    JonM Moderator

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    not all brass is the same. outside dimensions may vary slightly from brand to brand. measure the diameter of a known bullet. your caliper should be ok. just zero it out and get after it.
     

  3. aandabooks

    aandabooks Active Member

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    What brand caliper did you buy? Calipers generally are not the most accurate choice for measuring round items. If you want to get the most accuracy you need to buy a good 0-1" micrometer. Calipers rely too much on the operator being square to the part and using a consistant pressure time after time.

    That being said, calipers are faster to use than micrometers and if you purchased a digital set, they are easier to read at a glance.
     
  4. Richz99

    Richz99 New Member

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    It's a Lyman dial caliper; analog. I usually prefer analog over digital when it comes to precision measuring. Call me old school...
     
  5. noylj

    noylj Member

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    Consider manufacturing tolerances and then look at the case diagram. Do you see min/max tolerances? Do all you cases measure exactly the same?
    Measure case length. You will find that all your pistol cases measure less than the case drawing shows.
    Per SAAMI, the body diameter is x.xxx +0/-0.006.
    Go to http://www.saami.org/PubResources/CC_Drawings/Pistol/45 Automatic.pdf
    and
    http://www.saami.org/PubResources/CC_Drawings/Pistol/357 Magnum.pdf
    and study the drawings. There is no +/-, everything is +0/-x.xxx.
    We do not live in a perfect world, so dimensions do vary.
     
  6. c3shooter

    c3shooter Administrator Staff Member

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    Flashback- the day I came back from TDY, and found my bride had glued and clamped a broken widget using my Starret 0-1 mike. :eek:

    If you doubt accuract of a caliper or mike, use a known object, such as a feeler guage. Brass WILL vary.
     
  7. aandabooks

    aandabooks Active Member

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    Have never heard of Lyman. Calipers are generally sold with a +/- of accuracy stated. Get a gauge block so that you can periodically check your calipers for accuracy.
     
  8. Eric0424

    Eric0424 New Member

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    As mentioned before brass case dimensions will vary from what's listed and from one brand to another. They may even vary from one lot to another of the same brand. If it's any help, I just measured the rim (yes it is the rim you measured) on four pieces of Remington 357 brass and four Federal in 45ACP, the 357 has the same number you measured, the 45 measured .475". I get the same numbers with three different calipers, Fowler, some China knock-offs and my Browne & Sharpe. They all read the same measurements.

    Your caliper sounds like it's fine and you shouldn't have any trouble measuring round objects down to a .001" accuracy as most calipers are designed, including your Lyman.

    Never heard of Lyman?? They produce reloading and shooting accessories, and equipment.

    Lyman Products Your Primary Source for Reloading Equipment
     
  9. Richz99

    Richz99 New Member

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    Eric,

    Thanks for the help; I really appreciate it!

    Now it looks like I have a lot of reading ahead of me to ensure my first reloads don't blow anything up :)
     
  10. rjd3282

    rjd3282 New Member

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    I know that is sad but still a little funny. :D
     
  11. skullcrusher

    skullcrusher New Member

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    I don't know how old school you are, but precision measuring with calipers? That, good sir, is an oxymoron. Or, were you pointing to actual precision measuring?
     
  12. Logan2302

    Logan2302 New Member

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    If you want to satisfy yourself that your dial caliper is correct, zero it then check it with a 2 or 3" standard. How easy is that?
     
  13. Sniper03

    Sniper03 Supporting Member Supporter

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    As JonM stated. To do a close check on your Calipers. Pull a Bullet out of your Box read the dimension of the bullet on the end of the box and measure it. They should be very close!

    03
     
  14. Eric0424

    Eric0424 New Member

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    You're welcome. Reading a few loading manuals is what I did before actually loading anything, it helps to understand the how's and why's and avoid common mistakes before diving in head-first.

    ...and I too prefer using dial calipers, vernier micrometers and balance-beam powder scales over the digital.
     
  15. Richz99

    Richz99 New Member

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    Ok, Logan, I'll bite... Please explain.



    skullcrusher - Precision is of course relative. Where some people may use a ruler, I prefer a yard stick :D
     
  16. Logan2302

    Logan2302 New Member

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    There's no hook. A 'standard' is a precision ground length of rod that is certified to be as exact to a specific measurement, say 3", as humanly possible to measure by hand. When you buy a box set of micrometers you get enough 'standards' to check each mic from time to time.

    So, if you zero your caliper and then check a 3" standard it should read 3.000"
     
  17. grunt67

    grunt67 New Member

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    Richz99

    I don't know what a Lyman caliper looks like. I'll assume it's not made out of plastic. There are many brands of calipers out there, but any of them that meet industry standards will suffice. There should be an adjustment screw on the top of the dial. This will allow you to calibrate it against a known dimension, such as the diameter of a drill bit, 1/2 inch = .500, 1/4 inch = .250, etc., or as c3shooter suggests, feeler gages would be a good choice.

    A caliper is not a "precise" precision measuring tool, but precision is relatively "relative". Don't squeeze it too tightly or drop it on the concrete, keep the dust and crud away from it, and you'll be OK.

    Keep in mind, as noylj mentions above, every dimension you see will have to meet SAAMI specifications. There is always a tolerance "window". Example: Nominal size would be exact...but .005 below "exact" will fall into specs. Even bullet diameters will vary some....but you'd need more precise measuring equipment to know how much. Bullet diameters will be much more precisely controlled than the diameter of the base of a .45.

    "A couple 'thou ain't much, unless you're talking to your banker."

    Good luck!!

    PS: If you were really 'Old School', you would use a vernier, but personally, I like the newer stuff.
     
  18. Richz99

    Richz99 New Member

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    Logan,

    Thanks for the explanation. I'll admit I'd never heard of a 'standard', so I thought there was a hook. I also had to do a Google image search for a vernier :). I learn something new every day.

    Before I started this thread, I tried to find something with a known standard dimension but I couldn't think of anything. I tried coins, but they're all a little different and they didn't match the dimensions I found on the internet :mad: Who knew...

    Anyway, thanks for all the help.

    p.s. My wife has been doing the math on all of the stuff I've bought so far, and all the stuff I still need to buy, and she doesn't seem convinced when I tell her I'm doing this to save money.
     
  19. Eric0424

    Eric0424 New Member

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    They look like this:

    [​IMG]

    I've seen this exact caliper with half a dozen different names on it, Shars, Aerospace, SPI, now Lyman, they're decent calipers for the price. Not as nice as Starrett or Browne & Sharpe, etc. but they'll do the job.