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Thread: accurate weighing

  1. #1

    accurate weighing

    I am using a Target Master trickler and RCBS scales and also have a MTM mini electronic scales. It still proves to be difficult to get consistent accuracy better than .3 grn. Calibrating the mini is reasonably straight forward but if the loads weighed out by the trickler and the RCBS are checked on the mini they vary. Now this could be as it seems and the RCBS are being slightly inconsistent or as I seem to want to believe it is the mini not holding its calibration very well.

    Does anyone have any advice or thoughts how to weigh more accurately.

  2. #2
    Are you keeping the agate bearings and the knife pivot on the RCBS clean? Crud in the bearing channel will affect the scales accuracy and consistency.

    With my previous PACT(RCBS) Chargemaster scales/trickler set up the scales were affected by the weather and needed conditioning to the room for an hour or two before they settled.



  3. #3
    I would trust the RCBS before the MTM. I've compared my MTM to my Ohaus Dial-o-Grain and it was all over the place. Lose the MTM.~Muir

  4. #4
    Go and buy some Gempro scales very very accurate.

  5. #5
    Nothing wrong with RCBS above, check the agate bearings and pivot. If not already done, it is worth sending them off to be tuned. Fettled RCBS beam scales will measure individual kernels of propellant (I'd trust them over any electronic scales). I use a camera pointing at the scale, and view the pointer on my laptop screen. Unnecessary for stalking rounds but for target rounds I want them to be as consistent as possible and the RCBS I trust.

  6. #6
    If i where you i would send the target master and scales up here to me for a short holiday,and recalibrate the mtm,s till you get them back,

  7. #7
    Thanks Folks,

    Some useful ideas there. I think cleaning up the bearing first stop. Sorry AnDru youve got that the wrong way round, the scales like it here in sunny Devon, lifes a permanent holiday, perhaps the mtm might benefit from your kind offer!

  8. #8
    There are 2 aspects to consider with scales. The first is accuracy and this is defined as "precision" and means how the scale will actually report the weight. The scales will show a number that defines the accuracy - usually looks like "x0.1"
    The second is repeatability. The scales need to report the same weight every time. This is a function of many things. Scales should always be on a level hard surface and the weight always placed in the center of the pan. Ensure batteries are good and the scales are away from drafts. Always check with a test weight and always allow them to stabilise. Regularly check the tare. This also comes down to the "quality" of the scales - cheap ones can be accurate (x0.1 gram) but not repeatable, i.e. give a different answer each time you use them despite the test weight being the same.
    The MTM scales will show the test weight at 50 grams, but it could actually be 49.9 to 50.1 grams. I don't know how it is programmed to round up or down.
    You would expect the scales to round up at 0.05 grams as they can only display to 1 decimal point (tenths).
    If you convert this to grains it does actually mean that a 42 grain powder charge can range by +/- 0.8 grains and still be displayed as 42 grains on the scale.
    You can significantly reduce this by spending more money on a set of scales with an accuracy of x 0.01 grams which is about as good as you can get for sensible money and routine kitchen table/shed reloading. As a chemist I would routinely weigh to x 0.0001 grams.
    A 42 grain charge on a set of scales with accuracy x 0.01 gram will now only range by +/- 0.08 grains.
    With powders like Vhit (quite large grain size/weight) this will be about as good as you can get because you are now at the weight of single specs of powder.
    Last edited by stecad; 06-10-2016 at 08:09. Reason: Correct typo error

  9. #9
    What does the ammo shoot like?

    i started reloading with lee scoops.
    Still only using a cheap electronic scale and most often a lee powder thrower.

    pic to the left was thrown not weighed.

  10. #10

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