THR myth confirmation/busting - digital scale accuracy

[LiveLife]

Before anyone goes and orders a Gemini 20 ... the Gemini is an ultra economy scale and must be verified against a reloading check weight set (not the calibration weight).

If you don't have check weights, you should really get some first...scrap pieces of paper prove nothing.

Yes, definitely agree with the use of check weights.

But earlier in the thread, we already established that various .1/.02/.015 gr resolution scales were verified accurate with .5 gr check weights. The use of the 1/4"x1/4" pieces of paper was to determine some means of checking .1 gr which is below the lowest .5 gr check weight.

Can you even buy .1 gr check weight?

 

[Reloadron]

Can you even buy .1 gr check weight?

You can buy anything you want but weights like that get into a special order item. Companies like Mettler, Rice Lake, and Troemner will be happy to make and certify weights. They aren't cheap. Just a single 1 gn weight (leaf type style) runs around $20 plus cert if you want a cert. Anything less becomes a special order item.

Precision weights are also broken down by class unlike the simple check weights we use to check a powder scale. Hand loaders don't need weights like this.

Ron

 

[LiveLife]

This thread sure has been a learning experience.


Check weights come in following standards:

OIML R 111: E1-M3 - International Organization of Legal Metrology Recommendation - http://www.haefner.de/fileadmin/images/pdfs/EN_Haefner_price_list_2014_web.pdf

ANSI/ASTM E617: 1-7 - American National Standards Institute/American Society for Testing and Materials - http://us.mt.com/us/en/home/support...ile.res/OIML_and_ASTM-calibration-weights.pdf

OIML E0 / ASTM 0 - Primary/secondary mass standards
OIML E1 / ASTM 1 - Reference mass standards
OIML E2 / ASTM 2 - High precision weights
OIML F1 / ASTM 3 - Analytical weights
OIML F2 / ASTM 4 - Precision weights
OIML M1 / ASTM 5 - Precision weights
OIML M2 / ASTM 6 - Medium accuracy weights
OIML M3 / ASTM 7 - Commercial weights

Check weight sets we use for reloading fall into OIML M2/ASTM 6 class. Of course, you can get higher precision check weights but you have to spend more money.

Can you even buy .1 gr check weight?

Apparently you can. Not only that, you can buy check weights starting at 1 mg (.015 grain).

According to 2014 Häfner price list, 1 mg flat polygon sheet or wire check weight run $5 (M1), $11 (F2), $13 (F1), $70 (E1) to $112 (E0) EACH depending on standard class and whether aluminum, nickel silver or stainless steel.

I found Class 6 Ohaus 1 mg to 500 mg check weight set for $50 with free shipping - http://www.zoro.com/i/G0843236/?utm...506N8jrWKrMh_KzSVM1qhpAFU2BoC6Gnw_wcB&whence=

 

[LiveLife]

I ordered the Ohaus check weight set from Zoro ($50 + free shipping).

When I ordered the Gemini-20 digital scale from Amazon, I noticed the vendor also sold American Weigh Scales M2 check weight set that included 500 mg down to 10 mg weight and ordered the set also based on reviews. So my order came out to $19.74 for Gemini-20 and $10.40 for the check weight set (I ordered an extra set to get the Autoprime 2-day free shipping. I may PIF the extra check weight set ).

This is one of the reviews on the check weight set. I think accurate enough for reloading purposes - http://www.amazon.com/gp/pdp/profile/A1RH25QPHHDB40/ref=cm_cr_dp_pdp

American Weigh Scales Calibration Weight Kit WGHTKIT, Class M2

By Eran on October 6, 2011

I have tested my recently purchased weights kit with a calibrated analytical scale (1 mg accuracy):

50g weight: 50.015, 50.014 (<=0.03%)
1st 20g weight: 20.003, 20.004 (<=0.02%)
2nd 20g weight: 20.005, 20.005 (<=0.025%)
10g weight: 10.002, 10.003 (<=0.03%)
5g weight: 5.001, 5.001 (<=0.02%)
2g weight: 1.999, 2.001 (<=0.05%)
1g weight: 0.999, 1.000 (<=0.2%)
500mg weight: 0.500 (<=0.2%)
200mg weight: 0.200 (<=0.5%)
100mg weight: 0.099 (<=2%)
50mg weight: 0.050 (<=2%)
1st 20mg weight: 0.019 (<=10%)
2nd 20mg weight: 0.019 (<=10%)
10mg weight: 0.010 (<=10%)

 

[anothernewb]

perhaps this was answered already - so forgive me - but the pan on the Gemini looks pretty small. anyone hazard a guess as to how much powder it would hold?

 

[Reloadron]

perhaps this was answered already - so forgive me - but the pan on the Gemini looks pretty small. anyone hazard a guess as to how much powder it would hold?

Platform Dimensions 1.3” Ø

My RCBS has a useable platform width of about 1.5" so there isn't all that much difference. Surprisingly the Gemini 20 I ordered yesterday should be here today. Ordered early from Amazon using Amazon Prime, I expected it maybe tomorrow. I'll see which pans I have work with it but I don't see a problem.

As to the weight classes for standard weights. While all of this can be entertaining much of it will always revert to how good does a scale need to be for its intended application? Weighing powder charges for reloading isn't something that requires extreme accuracy and the use of super accurate check weights or calibration weights isn't really needed.

Without playing a Metrology game the accuracy ratio between the UUT (Unit Under Test) and the calibration standard should be 10:1 with a TUR (Test Uncertainty Ratio) of 4:1 acceptable in many cases and sometimes even a 1:1 TUR is acceptable. So a scale with an accuracy of +/- .1 grain really only needs a standard weight that is 10 times more accurate. Heck, for a powder scale even four times more accurate would be fine. You get to a point of diminishing returns.

Bottom line in my opinion is yes, the digital scales available to the hand loader are plenty accurate and reliable for loading accurate and safe ammunition assuming the individual doing the loading watches what they are doing. Just use good standard reloading practices.

I may be wrong but in 5 pages of post I only saw one negative comment regarding the use of digital scales and the poster failed to document why they disliked using a digital scale. The general consensus is they work just fine.

Ron

 

[cfullgraf]

I have not received my Gemini 20 scale yet, but i suspect a spacer could be made to raise any pan used to clear any interferences.

Material could be UHMW polyethylene, or maybe a ring cut from an appropriate diameter PVC pipe.

Just hit the tare weight button with the spacer and pan in place.

 

[Reloadron]

I have not received my Gemini 20 scale yet, but i suspect a spacer could be made to raise any pan used to clear any interferences.

Material could be UHMW polyethylene, or maybe a ring cut from an appropriate diameter PVC pipe.

Just hit the tare weight button with the spacer and pan in place.

Yeah, shouldn't be a problem to fabricate something. Mine arrived and it's funny. It weighs like nothing and is about the size of a wallet, maybe a little larger. It does work well from what I can see. I also used the pan it came with and set one of my other pans on top of it which worked.

So for the price not bad. I like my larger scales but only because they are easier to use because of their larger size and pans. Also the larger displays they have. However, that said this new little scale is pretty cool, tiny but not bad for the twenty bucks it cost. No doubt a large washer (thick washer) would work for supporting the larger pans. A thick rubber washer would likely work.

Glad you mentioned the tare function. People need to keep in mind that the max weight is just that, maximum weight which can be applied. So you can't for example place something outrageous like 1/4 the max on a scale and then add close to the max allowable on the scale to be weighed. While unlikely to happen worth noting with digital scales.

Ron

 

[lauderdale]

Thanks BDS, let me add it is a grams to grains check weight kit from review's as I have 4 scales an each have a how should I say different definition or abbv.. One says they have the go to chart from grams to grains. and reel impressive reviews. I would like to just get it in grains even for a few $ more?

 

[RedHawk357Mag]

How do these Gemini scales Handle wind currents? If a darn mouse farts in my garage the scale gets all out of sorts. Also keeping scale level to the Nth degree reduces most of my issues with drift.

 

[LiveLife]

With Amazon 2 day shipping, the Gemini-20 scale should arrive Thursday along with check weight sets down to 10 mg (.15 gr). So I will do some weighing of those check weights until Ohaus check weights arrive with 1 mg (.015 gr) check weight.

My Ohaus 10-10 scales are sensitive to air movement in the room so I usually turn off the AC and close the door. If you are using the scale in the garage that's affected by air movement, I would close the garage door or use the scale indoors.

I would like to just get it in grains even for a few $ more?

Most digital scales can have the reading mode switched from grams to grains.

 

[Reloadron]

How do these Gemini scales Handle wind currents? If a darn mouse farts in my garage the scale gets all out of sorts. Also keeping scale level to the Nth degree reduces most of my issues with drift.

Pretty much like any other sensitive scale the scale is susceptible to air currents and other outside forces that can act on it like vibration. Really high end laboratory scales have a glass case surrounding the measuring surface to eliminate the effects of air currents. So it is unwise to use a sensitive scale around heating and air conditioning ducts unless we do like bds does and turn off (eliminate) the outside forces that will effect our readings. Some users simply fabricate a protective box using for example an old shoe box or cardboard box.

Later today I hope to play around a little more with this Gemini 20 scale.

Ron

 

[lauderdale]

yes w/the gem pro. on its little pad I hate to have the bubble level on the pad they give you and it slips off! That is going from grams to grains and such. I made a check weight yesterday w/wire 0.005. as I turned the air back on it slowly drifted back up. Thanks I don't want to get to off topic!

 

[LiveLife]

UPDATE:

The Gemini-20 digital scale, Ohaus check weight set and the American Weigh Scales check weight sets were delivered today (I love Amazon's 2 day free autoprime shipping!).

To my surprise, the American Weigh Scales check weight sets included 1 mg (.015 gr) weight when it was advertised that 10 mg (.15 gr) weight was the lowest weight. As many suggested, I ditched the batteries that came with the scale and inserted two fresh AAA Duracell batteries. After calibrating with two 10 gram calibration weights that came with the scale, I was ready to do some weighing.

To eliminate the influence of air movement, air conditioning was turned off, reloading room door closed and bench leveled. All readings were taken with the cover applied over the pan. I also only handled the check weights and pan with the supplied twizzers.

- The 10 mg (.15 gr) check weight showed .010 g consistently but when I changed the mode from gram to grains, it showed .14 gr to .16 gr (was the scale expressing its .02 gr accuracy?).

- 1/4"x1/4" pieces of 20 lb copy paper showed .06 gr consistently and 2 pieces showed .12 gr.

- The 1 mg (.015 gr) weight would not register no matter what. I finally gave up and accepted defeat that the scale was not going to detect the .015 gr check weight.

I really was hoping the scale would read the 1 mg check weight so I recalibrated the scale a few times with no success, the 1 mg check weight would not register. At least, 1/4"x1/4" pieces of paper weighed consistently.

Then I weighed the 10 mg (.15 gr) check weight on the Ohaus 10-10 scale. It consistently showed slightly higher than .1 gr. When I placed one piece of 1/4"x1/4" paper, it detected and showed between two .1 gr lines. Two pieces showed around 1 gr with the pointer never below the .1 gr line.

Summary:

Pros:
- Low price ($20)
- Lower resolution than Ohaus 10-10
- Convenient pan cover

Cons:
- Small pan (holds about 35 gr of W231/HP-38 and 30 gr of Unique)
- Small round platform (slightly less than 3/4") will not accomodate a regular pan from 10-10/5-0-5 due to ridged ring around the platform
- Gap between round platform and the scale top will allow debri to fall in


Conclusion - It's always nice to have check weights. Since the scale read the .15 gr check weight between .14 - .16 gr, I would say reading of .06 gr for 1/4"x1/4" pieces of 20 lb copy paper may be close enough to express that two pieces of paper should weigh at or more than .1 gr. So if your digital scale cannot detect two pieces of 1/4"x1/4" copy paper and you want to load max charge loads, I would likely suggest you get a beam scale that can consistently weigh .1 gr.

I will keep the Gemini-20 digital scale in my reloading room but away from the bench so it can be stored without batteries in a location that is free from shock and vibration of bench work. I will continue to keep the Ohaus 10-10 on the bench at eye level and use it to verify powder measure charges. I will also keep my FA DS-750 with flat square platform that will readily accommodate the 10-10 pan to do quick spot verification of charges and weighing of bullets/rifle cases.

Why was I concerned with .1 gr accuracy when my typical pistol charges run 3.5 - 6.0 gr? Because I load near-max/max loads with WSF. I have always trusted beam scales and check weights down to .5 gr but being able to verify accuracy down to .15 gr with check weights puts my heart more at ease.

I thank all those who participated and contributed to this thread. It allowed me to satisfy one nagging aspect of reloading that digital scales (even cheaper ones) can be accurate enough for reloading, but they need to be verified with known weights like check weights.

Since I ordered an extra check weight set to get free shipping, I will be PIF along with my old set of check weights in a new thank you PIF thread. If you are interested in these check weights, post a reply. On 9/14/14, rcmodel or blarby will be selecting a random member from those that replied on the thread - http://www.thehighroad.org/showthread.php?t=760272

Good night and have a wonderful laborday weekend!

I will be taking the family up to the mountain/lake tomorrow so I won't be back until Saturday.

 

[Reloadron]

- The 10 mg (.15 gr) check weight showed .010 g consistently but when I changed the mode from gram to grains, it showed .14 gr to .16 gr (was the scale expressing its .02 gr accuracy?).

- 1/4"x1/4" pieces of 20 lb copy paper showed .06 gr consistently and 2 pieces showed .12 gr.

- The 1 mg (.015 gr) weight would not register no matter what. I finally gave up and accepted defeat that the scale was not going to detect the .015 gr check weight.

Yes, on the first one. You are seeing a result of what the scale can resolve. So the scale may be seeing .014 with a 1mg weight applied and it will display 0.00. There is also a matter of how the scale does the math and how today's digital scales actually work.

The weight on the paper sounds about correct. The scale is only capable of displaying .02, .04, .06 or .08, it will always be a 2, 4, 6, or 8 for the least significant digit. The scale will always round up or down depending on how it does the math functions.

Also bds you have an enjoyable and safe Labor Day weekend. We are going down to Columbus, Ohio to hang with family and see the brand new grandson born a few days ago. I have to wait till he is 2 weeks to take him to the range.

Ron

 

[anothernewb]

BDS - since the pan is so small, do you think it's possible to use much larger of a pan on it.

I was thinking about this one:
http://item.brownells.com/categories/rcbs-powder-handling/rcbs-scale-panfunnel.htm

I would happily paypal the cost of it to you for testing.

 

[LiveLife]

since the pan is so small, do you think it's possible to use much larger of a pan on it.

I actually have the same RCBS combination pan/funnel and thought the same but the bottom of the pan/funnel is 1" in diameter and since the bottom of the pan is wider than the round platform, it would rest on the body of the scale and not on the platform.

I guess I could use a short cylinder with diameter less than 3/4" and set the pan on top of the cylinder to clear the scale body. I could try that after we return from the mountain/lake on Saturday.

The weight on the paper sounds about correct. The scale is only capable of displaying .02, .04, .06 or .08, it will always be a 2, 4, 6, or 8 for the least significant digit. The scale will always round up or down depending on how it does the math functions.

That seems to be the case as the scale would read the .15 gr check weight as either .14 gr or .16 gr and pieces of paper at .06 gr and .12 gr. So my guesstimate of .05 gr for 1/4"x1/4" copy paper was not too far off? At least using 2 pieces to test accuracy of .1 gr resolution scales?

Also bds you have an enjoyable and safe Labor Day weekend. We are going down to Columbus, Ohio to hang with family and see the brand new grandson born a few days ago.

Thank you and will do. And congrats on the new grandson!

 

[higgite]

So my guesstimate of .05 gr for 1/4"x1/4" copy paper was not too far off? At least using 2 pieces to test accuracy of .1 gr resolution scales?

Theoretically in a perfect world, 0.048gr for 20 lb paper. But, you need to add for humidity and skin oil... and ink if it's used paper. Not too shabby for a SWAG.

 

[lauderdale]

Thank you SIR, and have FUN!

 

[LiveLife]

since the pan is so small, do you think it's possible to use much larger of a pan on it.

I actually have the same RCBS combination pan/funnel and thought the same but the bottom of the pan/funnel is 1" in diameter and since the bottom of the pan is wider than the round platform, it would rest on the body of the scale and not on the platform.

I guess I could use a short cylinder with diameter less than 3/4" and set the pan on top of the cylinder to clear the scale body.

UPDATE:

I tried different items but what worked well is a cut piece of 45ACP case to use as short cylinder. It is the right diameter to be set inside the round platform. I used the pan from Ohaus 10-10 and the Gemini-20 tared and weighed without issues.

So my guesstimate of .05 gr for 1/4"x1/4" copy paper was not too far off? At least using 2 pieces to test accuracy of .1 gr resolution scales?

Theoretically in a perfect world, 0.048gr for 20 lb paper. But, you need to add for humidity and skin oil... and ink if it's used paper. Not too shabby for a SWAG.

If it helps other THR members, this swagger will be a happy camper.

 

[LiveLife]

BTW, for those not familiar with SWAG:

Scientific Wild Ass Guess - http://en.wikipedia.org/wiki/Scientific_Wild-Ass_Guess


It was not a total guess as one 1/4"x1/4" piece of 20 lb copy/printer paper would show between .1 grain lines on the Ohaus 10-10 beam scale consistently and two pieces would show slightly more than .1 grain consistently.

That's why I asked for help from reloaders with higher resolution scales to verify the weight readings which ranged from .04 gr to .06 gr. So with those readings, I figured and estimated each piece should weigh around .05 grain and two pieces could be used as .1 grain pseudo-check weight to check the accuracy of .1 grain resolution scales if the lowest check weight in the set was only .5 grains.

Of course, as many posted, there are variables to factor such as humidity, moisture/oil from finger tips, etc. but we could minimize these variables by selecting a clean piece of paper from a new ream and using twizzers/forceps to handle the pieces of paper.


At least, it's better than nothing.

So if you come across a used beam scale and don't have a set of check weights handy (and even if you did and want to verify less than .5 grain detection), you can use 1/4"x1/4" pieces of paper to check the sensitivity of the scale. If the scale detects one piece of paper and reads around .1 grain with two pieces of paper, that scale is worth buying (BTW, that's how I tested my two Ohaus 10-10 scales before I bought them).

If your beam scale won't detect one or two pieces of paper, perhaps it's time to clean the agate stones and the knife edge.

If you have a .1 grain resolution digital scale, you may not see detection and reading until 2-3 pieces of paper are placed. If you see nothing, perhaps it's time to change the battery and recalibrate the scale. If you have a .02 gr resolution digital scale, you should see .06 grain for one piece and .12 gr for two pieces of paper.

Of course, check weights are always better and set that contains 10 mg/1 mg weights (.15 gr/.015 gr) could be bought for $10 (the product description does not mention 1 mg weight but it shipped with one) - http://www.amazon.com/dp/B003STEJAC/ref=pdp_new_dp_review

Hopefully this thread provided THR members/guests with something useful and at least, some amusement and fun with their scales.

 

[anothernewb]

UPDATE:

I tried different items but what worked well is a cut piece of 45ACP case to use as short cylinder. It is the right diameter to be set inside the round platform. I used the pan from Ohaus 10-10 and the Gemini-20 tared and weighed without issues.

Nothin like good old fashioned DIY!

 

[rg1]

Don't know how everyone cut EXACT 1/4"x1/4" pieces of paper. Mine weren't exact but marked and snipped out with scissors. Not a reliable check weight especially the method I used to cut the squares.

 

[LiveLife]

If you reload, you should have calipers which will give you precise measurement verification to .001".

 

[Ike Arumba]

Great thread, but it leaves me wondering which of these electronic scales are good for trickling.