Are check weights accurate?

[MongooseV8]

Start low and work up

[pennstater]

We have kcstott's post, which is pretty spot on. Then we get post #10. Really!?
Sometimes I just have to wonder about some posters here. Whew.

[RNE228]

What is the tolerance on the checkweights? Neither Lyman nor RCBS list tolerances on their websites.

If you have a 200gr checkweight, it's 200gr +/- some amount.

You're going to have some cumulative measurement uncertainty

[ar15barrels]

What is the tolerance on the checkweights? Neither Lyman nor RCBS list tolerances on their websites.

If you have a 200gr checkweight, it's 200gr +/- some amount.

You're going to have some cumulative measurement uncertainty

There are many defined tolerance classes.
There are also different standards organizations.
Troemner has the most common ones listed in their chart:

https://www.troemner.com/media/downloadablepdfs/tolerance/weight_tolerances.pdf

Note that the tolerances are given in milligrams for the weights below the point on each class where they list milligrams instead of grams.
Everything under 1kg is in milligrams.
When tolerances are not given, we assume the lowest tolerance range.

If we are calibrating for a 200 grain weight, a 10gm check weight will be the closest weight with a called-out tolerance.
13gr of check weight should register at 200.621 grains on a scale.
That's what I would use if I were checking a scale for accuracy at 200 grains.

My Troemner check weights came in a felt lined box and the instructions say not to touch them without lab gloves on.
They are to be lifted with a lifting tool and kept in their sealed box when not in use.

[RNE228]

Yes, working in a test and measurement lab the same applies to DVM, Oscilloscope etc. Another lab next to me uses digital scales all the time; they have screens around the scales so the air conditioning does not blow on the scale and throw the readings off.

In the context of this thread, this was not part of the consideration.

I was surprised though, that neither Lyman nor RCBS listed any references for tolerances.

There are many defined tolerance classes.
There are also different standards organizations.
Troemner has the most common ones listed in their chart:

https://www.troemner.com/media/downloadablepdfs/tolerance/weight_tolerances.pdf

Note that the tolerances are given in milligrams for the weights below the point on each class where they list milligrams instead of grams.
Everything under 1kg is in milligrams.
When tolerances are not given, we assume the lowest tolerance range.

If we are calibrating for a 200 grain weight, a 10gm check weight will be the closest weight with a called-out tolerance.
13gr of check weight should register at 200.621 grains on a scale.
That's what I would use if I were checking a scale for accuracy at 200 grains.

My Troemner check weights came in a felt lined box and the instructions say not to touch them without lab gloves on.
They are to be lifted with a lifting tool and kept in their sealed box when not in use.

[ar15barrels]

I was surprised though, that neither Lyman nor RCBS listed any references for tolerances.

Probably ANSI class 7 and they don't want to brag about that.
Maybe even so bad that they don't meet any class requirement.
21 mg tolerance for a 10gram class 7 weight is 0.32 grains.

[Dirtlaw]

I have been having a problem with my RCBS 5-10 scale so I acquired an RCBS M500 scale. I have a set of Lyman check weighs from .5 to 210.5gr. Using my check weights I'm finding the M500 to have a discrepancy of up to .4 grains at 200 grains. (Weighing 200.4 grains). I'm not sure if the problem is the scale or the weights. I have no idea where I can go to have the check weights calibrated or certified. Any suggestions?

Actually if you want to be really certain you need accurate reference weights. Better quality than you have is available on ebay. Of course, the more accuracy you want, the more money you pay. Lab grade can be expensive. But your fingers and hand might be worth it. Handle reference weights with special cloth gloves.