Some info about scales & calibration

[Oreo]

Here's some good info I found while researching which scale to purchase.

http://digitalscale.com/brands.htm - A forum dedicated to scales. Some professional reviews of both models & brands in general, and a list of preferrred on-line merchants.

Important info on calibration weights:
Most calibration weights commonly included with consumer level precision scales like the ones we use to measure powder are of OIML class M2 or M3 level or alternatively, ASTM class 6 or 7. These weights allow a maximum error of up to .4 grains! That's way too much for a lot of us. The M1 / class 5 level is much better suited to our scales. This class of calibration weight allows for a maximum error of .05 grains which will preserve the .1grain accuracy shown on most reloading scales.

This doesn't mean you need to go buy a new calibration weight necessarily. But if you buy a new scale, or need to replace a lost calibration weight you should be aware that there may be some variance from numbers obtained with the old equipment. Be careful with your max-loads for a bit. This could also be a cause of inaccuracies in published data or data posted by other reloaders.

http://www.oiml.org/publications/R/R111-1-e04.pdf?bcsi_scan_FBA36CC5DE08E987=0&bcsi_scan_filename=R111-1-e04.pdf - This is a PDF that gives the technical specifications for calibration weights.

http://balances.com/sartorius/calibration%2Bweights.html - Here's a place that sells high quality calibration weights & has a bunch of the info in that PDF listed in easier to read format.

http://scalesusa.zoovy.com/category/weightstestcalibrat.e_gram_weights/ - This place has much better prices but the calibration weights aren't NIST certified & aren't a solid one-piece mass, so I'm slightly skeptical of their quality.

[Tailgunner]

Absolute accuracy is nice, but not critical. Repeatability is critical.
You do realize that NIST requirments require "certified" weights to be re-calibrated every 2 years inorder to maintain there cert?
This is just another of the reasons that you work up a load for yourself, rather than going straight to the powder charge you found on the internet.

IOW I don't care if my 50gr weight actually weighs 49.7 or 50.3gr (accuracy) as long as my scale reads the same thing every time (repeatability). Measuring tools also require calibration on a annual basis, had your calipers calibrated lately?

[Oreo]

Yea, I get exactly what you're saying. Mostly, I'm listing a bunch of URL's & making notes so that I can find them later.

I think I covered the issue with repeatablity. Just be carefull if you're changing equipment.

From what I've been reading though, if your calibration mass is adjustable (the knob usually unscrews & theres a clay or soemthing inside) there may be a minor issue of repeatability over time. The solid stainless steel ones will be accurate enough for our purposes for a lifetime.

I have reason to suspect that the calibration weight that came with my scale is not accurate. So if I can find a solid one-piece 20g mass for a few bucks I'll pick it up.

[Tailgunner]

NOT trying to bust your chops.
It's a tender topic for me, I used to do NIST tracable calibrations as part of one of my previous jobs.
Weights should be solid, never "adjustable". They are normaly made heavy, and than drilled to tune. If they drill out to much weight, they drop to the next lower class(fillers are not allowed in certified weights).

IIRC there is about 15gr / g, so wouldn't you be better off looking for a 1 or 2g weight? Alum, brass or SS all work well in that range.

[Oreo]

Weights should be solid, never "adjustable". That's exactly my point. They ship cheap weights with some of the scales we buy. Or at least mine came with one. I want a better one that is built as you describe.

I need a 20gram weight to calibrate my scale. I don't think I can calibrate it to any other weight.

[Tailgunner]

I need a 20gram weight to calibrate my scale. I don't think I can calibrate it to any other weight

I see, and understand your delema now. Check with your local HS or college science dept, they should have a decent set of scales, and be able to give you a good idea of where your current weight is at, and/or weigh up a random chunk of metal for you to use (they may even "donate" a 20 gram weight to your cause).
I'll dig around at home this weekend, and see if I can scare up something you can use.

[Oreo]

I appreciate that man but I think I just got it all worked out. Thanks though. :)

[jmacken37]

I need a digital scale. Oreo, did you find a good deal on one?

Thanks,

Jake

[Oreo]

Are you looking for a good scale or a cheap scale? Jennings seems to make some good scales that sell for less then $100.