1. Attention: We have put together a thread with tips and a tutorial video to help with using the new software. Please take a moment to check out the thread here: Trapshooters.com Tutorial & Help Video.
    Dismiss Notice

bore gauge accuracy

Discussion in 'Shooting Related Threads' started by Johnny, Oct 10, 2011.

Thread Status:
Not open for further replies.
  1. Johnny

    Johnny Well-Known Member

    Joined:
    Jan 29, 1998
    Messages:
    2,804
    All gauges have a tolerance. What is the norm for bore gauge accuracy?
     
  2. BigM-Perazzi

    BigM-Perazzi Well-Known Member

    Joined:
    Jan 29, 1998
    Messages:
    8,542
    Location:
    HELL, MICHIGAN
    Generally 1/10 of the calibrations as I scratch my head.

    So, .001 would be+/- .0001

    Or 1/5, my memory not too good..
     
  3. Johnny

    Johnny Well-Known Member

    Joined:
    Jan 29, 1998
    Messages:
    2,804
    BigM, .0001 is hardly anything. So if I am seeing +/- .001 variation on the same repeated measurement that is not acceptable for a bore gauge?
     
  4. skeet_man

    skeet_man Well-Known Member

    Joined:
    Jan 29, 1998
    Messages:
    10,528
    Location:
    Rochester, NY
    They are typically +-.001. Anything more accurate than that and you're going to be spending thousands of dollars. Because of this, bore gauges should be used more as a comparison tool (measure the ID of the barrel, and subtract the ID of the choke) than as something that will give you a definitive measurement of either.
     
  5. BigM-Perazzi

    BigM-Perazzi Well-Known Member

    Joined:
    Jan 29, 1998
    Messages:
    8,542
    Location:
    HELL, MICHIGAN
    Depending on the type of bore Gage. The 3 ball Gage, you have to read the highest reading. It's hard to maintain it perfectly perpendicular to the bore. You can generally rock it side to side slightly to get the highest reading which should repeat. If we're talking timbered, I certainly wouldn't sweat the difference.

    Damn spellchecker I mean talking gun barrels!!
     
  6. BigM-Perazzi

    BigM-Perazzi Well-Known Member

    Joined:
    Jan 29, 1998
    Messages:
    8,542
    Location:
    HELL, MICHIGAN
    Johnny, in my line of work, .000010 can be too much!!

    Skeetman, I think your confusing calibrated increments with tolerance. The tolerance for repeatability should always be less than the increment of measurement...
     
  7. dverna

    dverna Active Member

    Joined:
    Jan 29, 1998
    Messages:
    2,717
    Does it really matter if it is .7375 or .738? Or if a choke constriction is .0295 or .030? I think we get too anal at times.

    BTW, it is easy to check with a "known" reference. Have old choke tube you no longer use verified at a good shop that is ISO certified, and compare it to what your device measures. Keep it as your "standard".

    Don Verna
     
  8. Johnny

    Johnny Well-Known Member

    Joined:
    Jan 29, 1998
    Messages:
    2,804
    BigM, "You can generally rock it side to side slightly to get the highest reading which should repeat."

    Yes, I understand that. When you say "should repeat" what is acceptable? Is +/- .001 normal? If I am a couple thous. off on the barrel and a couple more on the choke I don't know what I have. Seems it should repeat within .001.
     
  9. Johnny

    Johnny Well-Known Member

    Joined:
    Jan 29, 1998
    Messages:
    2,804
    dverna, If I could read that close everytime I wouldn't be asking this question. I do have chokes that are marked and I can read the marked measurement with calipers. Sometimes the bore gauge is right on sometimes of several thous. Hences the question about what is practical accuracy with these gizmos.
     
  10. BigM-Perazzi

    BigM-Perazzi Well-Known Member

    Joined:
    Jan 29, 1998
    Messages:
    8,542
    Location:
    HELL, MICHIGAN
    It depends on the dial indicator. If its not repeating there might be old oil in it or dirt. But, if its coming back within. 002 don't sweat it. Now were not talking day to day variations, right? You need to recalibrate to a known reference each time you use it like Don said due to temperature variations.
     
  11. Johnny

    Johnny Well-Known Member

    Joined:
    Jan 29, 1998
    Messages:
    2,804
    BigM, No, I am talking about consecutive readings, say minute. If the barrel reading says .735 one time and .736 the next is that normal accuracy? strange part is when checked with the calibration ring it zero's every time or very close. If the barrel reads .736 and I push on the button, it will return to .735. Is that normal? I am beginning to think what I see is normal and just the way it is.
     
  12. birdogs

    birdogs TS Member

    Joined:
    Jan 29, 1998
    Messages:
    2,775
    There are also variations in the bore diameter in the same barrel. If you move the gauge up or down the barrel you will notice the dial moving, sometimes quite a bit. A dear frriend, now departed who was a noted gunmaked told me that when he was in Italy he wanted to buy a number of barrels. As he mic'd them he noted that there was a great deal of fluctuation in bore diameter. The manufacturer merely shrugged his shoulders and told him. "That's how it is"!
     
  13. Johnny

    Johnny Well-Known Member

    Joined:
    Jan 29, 1998
    Messages:
    2,804
    unloader, I see there four screws on the back. I will keep that in mind.

    Pat, I think it does work best going from bottom and up.

    birdogs, I don't have noticable variation in the barrel and I have measured it full length. Doesn't move a tic as I go through the barrel, and it's just a BT.
     
  14. Ahab

    Ahab Well-Known Member

    Joined:
    Jan 29, 1998
    Messages:
    3,650
    Most of the variatons can be contributed to "operator error"!

    95% of the shooters don't really know how to use measuring instruments.
     
Thread Status:
Not open for further replies.