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Thread: variation in bullet diameter for same calibre

  1. #1

    variation in bullet diameter for same calibre

    I am starting to take an interest in loading my own .270 rounds and in a fit of boredom thought it might be interesting to look at the difference in two factory loads I use, RWS and Norma both 150gr.

    thing that struck me is the bullets are different diameters at .277 (norma) and .278(RWS) (actually between .2781 and .2784 if I am going to get pedantic)

    It doesn't seem much but it is visually noticeable and surprised me!

    is this unusual?
    all seems to come out the hole at the other end quick enough.

  2. #2
    No it's not unusual at all. The actual groove dimension for a .270 Win is 0.278" so a bullet of 0.2771" is undersize. That's not new either as Ken Waters made comments on this in his Pet Loads series and Ken has been dead for some years now.

  3. #3
    Quote Originally Posted by bewsher500 View Post
    I am starting to take an interest in loading my own .270 rounds and in a fit of boredom thought it might be interesting to look at the difference in two factory loads I use, RWS and Norma both 150gr.

    thing that struck me is the bullets are different diameters at .277 (norma) and .278(RWS) (actually between .2781 and .2784 if I am going to get pedantic)

    It doesn't seem much but it is visually noticeable and surprised me!

    is this unusual?
    all seems to come out the hole at the other end quick enough.
    I deal with small dimensions all the time and I can't tell two cylinders, .0014" difference in diameter, apart. You're good!~Muir

  4. #4
    ha, thanks. reflection on the edge was different and prompted me to measure it!

  5. #5
    Quote Originally Posted by bewsher500 View Post
    It doesn't seem much but it is visually noticeable and surprised me!
    Wow!!
    you must have shadowgraphs built into you eyes, i defy anyone to tell the difference between a .257 and 6.5mm bullet with out measurement

    WB.

  6. #6
    well I wouldn't have measured the diameter it if I didnt think there was a difference, so actual or perceived....it looks different....

    thats not really the point though.

    is it common for different manufacturers to use land bore diameter vs groove bore diameter for bullets?

    doesnt it make a difference?

  7. #7
    Well if you think about it not all bullets are made exactly the same. Differences in core hardness and even material and jacket thickness and even bullet shape will all effect the way a bullet behaves in the bore so obviously there will be diffferences. After all bullet makers don't just think up a design throw it into production and sell it to the world without testing them .

  8. #8
    This is why data for one bullet is not transferable to another. Different diameters will create different pressure curves even among similar descriptions of bullet weight /type between different manufacturers.

  9. #9
    Quote Originally Posted by longlowdog View Post
    This is why data for one bullet is not transferable to another. Different diameters will create different pressure curves even among similar descriptions of bullet weight /type between different manufacturers.
    Hmmm well Hodgdons for one seem to disagree as they just list bullet weights surely. Also as the accepted handloading practice of starting new loads from the start or a reduced charge weight you should not really run in to any safety problems.

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