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Old July 20, 2010, 05:33 PM   #1
jmak
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How do you check a scales accuracy without check weights?

I purchased a used RCBS 505 scale a while back and wanted to know if there is a way to check the accuracy for 10 -15 grains of powder? I know they sell check weights but I don't really want to spend $25.00 to get a set. It is the only scale I own.

Thanks,
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Old July 20, 2010, 05:37 PM   #2
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Well, you've got to have something of known weight. To get a general idea you can use bullets, as they are almost always within less than .5gr of intended weight and many are within .1gr. This is really only a ballpark number though.

To get more exacting, 1 cubic centimeter of water weighs exactly 1 gram at 0 centigrade.


Basically, you need a check weight but you don't have to pay anywhere near $25. Here's one for less than $6, delivered.
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Old July 20, 2010, 05:42 PM   #3
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A newish dime weighs 35.0 grains. A nickel weighs 5.00 grams.

I wrote "35" with a Sharpie on a dime and that is my standard check weight. I declare it to be exactly 35.0 grains. The actual exact amount is really not important; it is close enough, and more importantly it is repeatable because I use the same one every time. HTH
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Old July 20, 2010, 05:44 PM   #4
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You can use coins.

US coins are held to a very high weight standard.

http://www.usmint.gov/about_the_mint...specifications


You just need to convert grams to grains, which is easy with google.

According to google, a quarter is:

5.67000 grams = 87.5014719 grains

A quarter and a dime will be just a hair over 126 grains.

The newer the coin you use the closer it will be to specification.
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Old July 20, 2010, 05:50 PM   #5
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Coins! Dang! I would have never thought of coins.
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Old July 20, 2010, 06:29 PM   #6
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Thanks guys for the quick responses and the great idea about using coins. I thought about coins but didn't know how accurate they were when minted and how much the weight changes from dirt and wear. It sounds like a couple of clean new coins should do the trick for me. I can then mark them and stash them away as my check weights. This is a great forum to get creative answers to some not so common reloading questions.

Mike,
Just a quick correction in case someone else references this thread. A quarter and a dime actually weight 35 + 87.7 = 122.5 grains. A quarter and a penny weight 126.08 grains.

Thanks again,
jmak

Last edited by jmak; July 20, 2010 at 06:50 PM.
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Old July 20, 2010, 06:57 PM   #7
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I would not trust a penny because they keep changing the composition.
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Old July 20, 2010, 07:40 PM   #8
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I'm cheap. I use bullets. Same individual bullets each time, so I'm calibrating to the same weight.
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Old July 20, 2010, 07:58 PM   #9
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Interesting, I knew my money was worth less. A nickel and a penney came out at 7.44 grams, but both of my check weights of 50.0 grams came out right on the money, now if only the money would (LOL).


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Old July 20, 2010, 08:10 PM   #10
noylj
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Check Weight

Buy check weights
Call a local lab and see if you can have someone weight a few coins and bullets for you
Call a local jeweler and see if you can have someone weigh a few things

If you want to have fun, compare check weights if you have a couple of friends. The reloading companies are NOT supplying certified check weights. The key for any individual is to calibrate using the same check weight for internal consistency.
Just so you know what certified check weights are:
(Note: this is only a class 2 set for general lab work)
Class 2 calibration weight set (PWB7224-2W) consists of 9 pieces ranging from 1g to 100 grams, includes NVLAP Certificate of Calibration. Typical lead time is 7 to 10 business days from the date order is placed to shipping from NVLAP metrology lab. These ANSI/ASTM Class 2 can be used as reference standard in calibrating other weights and appropriate for calibrating high-precision analytical balances (from 0.001mg to 0.01mg).
Construction: The weights in this weight set are of 2 piece construction with handling knob. They are highly polished alloy stainless steel weights.
Weight Set Configuration: 100 g, 50 g, 2-20 g, 10 g, 5 g, 2-2 g, 1 g.
The weight set comes with a case made of Polypropylene with individual compartments for each weight; includes forceps.
The total capacity of the weight set is 210 g.
YOU PAY $776.00
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Old July 20, 2010, 08:12 PM   #11
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Quote:
A newish dime weighs 35.0 grains.
I keep a few new coins in a baggie with my scales for just that purpose.
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Old July 20, 2010, 08:13 PM   #12
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Lapua bullets

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Old July 20, 2010, 09:47 PM   #13
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Gee, and all this time I thought all you had to do was zero out your scale with the pan on it and start weighing. I also have a check weight or two but mostly I just zero out the scale and start weighing my powder I through or throw (Still can't spell) and start loading.

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Old July 21, 2010, 12:16 AM   #14
Mike Irwin
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"Just a quick correction in case someone else references this thread. A quarter and a dime actually weight 35 + 87.7 = 122.5 grains. A quarter and a penny weight 126.08 grains."

Whoops, yep.

"I would not trust a penny because they keep changing the composition."

Any penny minted in the last 5 years was minted to current standards as listed on the Mint's website.

I think prior to 5 years ago they were a little heavier, but not much.
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Old July 21, 2010, 12:57 AM   #15
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If you know someone with a RCBS 10-10 scale, the attachment weight is 250 grains. It avoids the grams to grains conversion.
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Old July 21, 2010, 07:05 AM   #16
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Zippy that is correct. All of my powder loadings are at the other end of the scale in the 3.0 to 7.0 grams range. I would prefer to test around the range I am loading. I bought the RCBS test weights but find that when I test out 5 grains and test 15 grains i'm still a little off. It's been a couple of months so maybe I'll try cleaning the scale and retest. For now I just set everything to Zero and ballance and start loading.
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Old July 21, 2010, 08:56 AM   #17
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It would appear the system we use for weight, volume and area is not related, but the metric system when determining weight, volume and area only require a ruler.

http://hypertextbook.com/facts/2002/...tOkereke.shtml

The .01 cent coin went from copper to zinc in 1982, in 1943 the .01 cent coin was steel/zinc coated, A warning, the zinc .01 cent piece when swallowed by a pet can kill the animal.

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Old July 21, 2010, 09:01 AM   #18
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What is your life worth?

A set of check weights is mandatory IMO. We are potentially talking life and death here. I know this sounds extreme, but I found I was much much more comfortable with my scale after I acquired a set of check weights. It is worth it for the peace of mind it will give you.
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Old July 21, 2010, 09:30 AM   #19
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What if the check weights are made from atomically unstable materials, and go super critical when you drop them into the pan? Then how good of a deal were those weights?





While anything is certainly possible, I would think a scale would really have to be REALLY out of whack for it to start dropping truly dangerous loads.
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Old July 21, 2010, 10:01 AM   #20
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Actually, Mike, that's sort of what has been happening with a few of the various official 1.0000000000000000000 Kg weights. (Zero's for effect)

Apparently, there are minute traces of radioactive materials in some of them that have now decayed and caused some the official kilogram weights to weigh less than some of the other official kilogram weights.
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Old July 21, 2010, 10:36 AM   #21
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The international standard is scheduled to change some time next year to an inertial property definition and away from the IPK (International Prototype Kilogram) in France. That should cure the drift problem caused by decay (lowering mass) and by oxidation (increasing mass). Mass is the last remaining standard based on an artifact rather than a property definition.

I would discourage using coins. This topic came up on another forum a couple of years ago, so I weighed 35 quarters on my Acculab scale and got:

Mean (average) weight:
87.62 grains

Highest:
89.02 grains

Lowest:
85.70 grains

Extreme Spread:
3.32 grains

Standard Deviation:
0.78 grains from mean.

That SD means, assuming a normal distribution, about 68.3% of all quarters should be within 0.78 grains of 87.62 grains, 95.4% will be within 1.56 grains, and 99.7% will be within 2.34 grains of that number. Not really good enough to do much of anything with for loading.

I haven't reread the whole thread, but if I recall correctly it turned out aspirin tablets came closer. That surprised me as I would expect some moisture pickup variance.

Volume of water can be used if you use distilled water, out-gas it and use a table or formula for volume verses temperature to correct it. The problem is that now you need a calibrated volumetric measure and thermometer. Not really a savings.

If I couldn't afford a check weight, I would cut a piece of stainless wire to about the weight I was most interested in, then go to my local pharmacy and ask the pharmacist if he had an accurate scale he could weigh it on for me? Scales of the type pharmacies use are often 0.001 gram (0.015432 grains) resolution and are sent to a calibration lab every year for re-certification against NIST traceable standards. If he calibrates it with his own check weight first, it should give you a pretty good number.
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Old July 21, 2010, 10:55 AM   #22
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Isn't that why we initially reduce the load data and sneak up to it instead of starting right at the max loads? (well, some of us do that) To reduce variances caused by different lots of powder, different primers, thicker brass, bad hair day, etc. Your check weight gives you a way to calibrate your scale back to where it was last time you calibrated it (to eliminate one variable) and to sanity-check the readings. ±2% is probably close enough for that, as long as you use the same check weight every time.
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Old July 21, 2010, 11:52 AM   #23
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Berger Bullets....dead nuts on!
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Old July 21, 2010, 11:53 AM   #24
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Zxcvbob,

That works as long as the shooter knows to take the added step of subtracting the expected error percentage from manual starting loads before he begins a work-up. Having twice encountered manual starting loads that were already at or above maximum for the gun I used them in, I would consider that a minimum added safety step requirement for using an approximate weight in place of a true reference.
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Old July 21, 2010, 12:11 PM   #25
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Quote:
Originally Posted by Jim243
Interesting, I knew my money was worth less. A nickel and a penney came out at 7.44 grams, but both of my check weights of 50.0 grams came out right on the money, now if only the money would (LOL).
Is that using a digital scale or beam balance? I've seen digital scales self-adjust to the check weights.
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