accurate weighing

WTF

Active Member
#1
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
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.

Cheers

Fizz
 

Muir

Well-Known Member
#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
 

ChesterP

Well-Known Member
#5
Nothing wrong with RCBS scales...as 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.
 

WTF

Active Member
#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!
 

stecad

Well-Known Member
#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.
 
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bewsher500

Well-Known Member
#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.
 

Triffid

Well-Known Member
#11
Get some calibration weights.

It was a real eye-opener for me when I started comparing my scales against calibration weight, both for accuracy (does a 20gr calibration weight read 20gr) and repeatability (does the indicated weight change during repeated weighings). I found the MTM scales complete rubbish and would only use them now for weighing bullets. My elderly RCBS scales were not much better, so I sent them off to Alan at Targetmaster (1066 here) for a service. They came back absolutely spot on and I'd highly recommend this.
I've also just bought some better quality electronic scales ( Smartweigh GEM50 off Amazon) and am giving them a test against calibration weights at the moment.

Triffid
 

Brimfire

Well-Known Member
#13
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.
A set of balance beam scales. You can see what your powder charge is doing. A Chronograph will tell you exactly how accurate your charges are.

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Don't confuse consistent charges with tight groups, as that chronographed home load although better accuracy than the factory loads was not the accuracy I was looking for.
 

Muir

Well-Known Member
#14
A set of balance beam scales. You can see what your powder charge is doing. A Chronograph will tell you exactly how accurate your charges are.

View attachment 75141

Don't confuse consistent charges with tight groups, as that chronographed home load although better accuracy than the factory loads was not the accuracy I was looking for.
Perhaps. If everything else is equal in the loading chain for each round. One hundred percent correct.~Muir


 

ChesterP

Well-Known Member
#15
+1 to the above. "Everything else is equal in the loading chain" especially neck tension. Equal charges will get you part of the way there but you may not get the SD/ES down unless neck tension is consistent.
 

Brimfire

Well-Known Member
#17
Perhaps. If everything else is equal in the loading chain for each round.~Muir
I was making that assumption when I made the statement about the Chronograph verifying your loading accuracy. I should have been more concise with my statement. A fastidious approach to reloading should reward a home loader with consistent ammunition.

When conducting long loading sessions I often recheck the zero of the balance beam. When all other procedures in the loading process are completed correctly, I like the reassurance that my scale is accurate. Then my COAL is stringently measured and checked with a bullet comparator, then an appropriate crimp. This allows me to reasonably assess the loaded ammunition and if I have done my part on the trigger correctly, the groups will be honest according to the developed load. The Chronograph is an invaluable tool in that assessment. An experienced person like you doesn't need to be told that!.... it was for the benefit of a new person interested in taking up home loading. However many people get hung up on velocity, when accuracy is the single most important factor.
 

stecad

Well-Known Member
#18
Just out of interest what range e.g +\- 25 fps, would you expect to see on the chrono for a home load that was made with all parameters ( powder, neck tension, etc) optimised?
 
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Brimfire

Well-Known Member
#19
Just out of interest what range e.g +\- 25 fps, would you expect to see on the chrono for a home load that was made with all parameters ( powder, neck tension, etc) optimised?
Absolute perfection would be 0fps ES. I can achieve a 20 shot string of <10fps ES with .30-06 projectiles travelling at an average 2720fps
 

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