A way to check the accuracy of your scale

[tmccray45]

As I'm weighing my powders, I often wonder, "How do I know that my scale is accurate?" Sure, I've been assured by the manufacturer that it's accurate down to the weight of a gnat's eyelash, but how do I know?

"I know, I need a standard of some sort that I can use to check the scale." But, what to use? I know that the French are not going to ship the International Prototype Kilogram (IPK) which is stored in a vault in Sèvres, France, so what can I use that is fairly easily obtained?

How's about good ol' American coins? I bet the U.S. Mint has standards that are fairly accurate for our coins.

Sure 'nuff, if you go to the "specifications" page of the U.S. Mint, you can find the weights of the various coins we use. The United States Mint Specifications page can be found at:
http://www.usmint.gov/about_the_mint/?flash=yes&action=coin_specifications

The coin weights are given in grams, so to convert grams into grains, you multiply by 15.4323584. Given that, you find that:

Penny = 2.500 grams = 38.58 grains
Nickel = 5.000 grams = 77.16 grains
Dime = 2.268 grams = 35.00 grains
Quarter = 5.670 grams = 87.50 grains
Half Dollar = 11.340 grams = 175.00 grains
Presidential $1 = 8.100 grams = 125.00 grains

Of course, you should select newer coins with a minimum of wear in order to come closest to the standard weight, but using these coins, you can come pretty darn close to checking your scale.

 

[Orange Boy]

Interesting. I think I'll get together ten new pennies and check them on my grain scale for deviation in weight.

 

[loadedround]

Interesting observation...do the old silver dimes and quarters weigh the same as the clad coins? How about the buffalo nickel vs the Jefferson nickel? I won't even bring up the Indian Head penny!

 

[oneounceload]

The newest coins are closest to those specifications

 

[rcmodel]

Not close enough for me to be using coins for reloading scale check weights.

I just weighed five each fairly newish:
Pennys (38.58) ranging 38.6, 39.0, 47.3, 48.0, and 48.1.

Nickles (77.16) ranging 76.2, 76.6, 76.7, 76.9, and 77.4.

Dimes (35.0) ranging 35.0, 35.0, 35.2, 35.3. and 35.5.

On the other hand:
Five 55 grain Hornady V-Max bullets all weighed 55 grains exactly.

rc

 

[Randy1911]

If you are that concerned, just buy a set of scale check weights. they are certified weights. They are available at most reloading stores online like Midway, Graf's just to name a couple.

 

[qajaq59]

You could weigh a penny on the day you get the scale and then keep it forever. That way, even if you were wrong, you'd be consistant.

 

[Mal H]

Nope, not close at all. I suppose you could use a coin as as a gross check weight just to see if your scale is broken, but to use it as a calibration weight is foolhardy.

I also weighed a bunch of pennies and got a range of 38.1 grains to 38.9 grains for the most recent mint years (Cu-Zn alloy). If you go back to years when the copper content was much higher, the range was around 47.0 to 48.1. Even pennies from the same year had more variance than would be healthy for reloading purposes.

 

[jcwit]

Personally I think being consistant is more important than being dead nuts accurate, unless one loads to the max, and frankly I think the powder mfg's have a safety factor built into their data anyway.

But this is just my opinion.

 

[fguffey]

Hind sight, I do not want to waste your time so I will not say it can not be done, but had you stamped an index (as in #1-#20) on 20 coins in the beginning when the scale was new and calibrated you could have a record to compare the accuracy of the press from then to now, It is not too late, a set of standards cost about $40.00, again I would not average 10 coins, I would stamp the coins and use them to check the press by adding each coin. and by numbering the coins you would know how much each coin weighed.



F. Guffey

 

[Sidewinder72]

I use check weights for my own peace of mind. They keep my digital honest. It sure gives you confidence in precise loads.

 

[twofifty]

let pharmacist weigh your 'check weights'

I use a few coins and bullets for check weights.

My pharmacist weighed these on his dispensing scale, in grams.
I converted from grams to grains, then made a note that I keep with my 'check weights' in a small plastic box.
Simple and free.

A reminder for new shooters:
it is important to store your scale under cover, so dust does not settle on it. It takes very little to put off a beam scale, or to slow/impede its movement. Periodically, run a Q-tip with alcohol on the pivot points and the agate bearings.

 

[MissouriCrowinMass]

TMCCRAY,

Great tip. A new dime is about 35.0 grains!! I weighed a few and got +/- about .2 of a grain. Pretty good.

I use two cheap Electric Scales. A NEVA and a DigiWeigh. They're usually about .1 grain apart. Amazing for about $25 each.

I found one dime that's 35.0 on the DigiWeigh and 35.06 on the Neva. Formerly, I'd proof the scales on good bullets just to assure myself that I was in a reasonable range of accuracy before a reloading session. I set my Powder Scale off the average of the two cheapo scales and then check about every 25th load with one scale. I reload for target shooting and stick in the middle of the recipes so I'm happy.

I'm a real skeptic. I would trust an average of a few dimes over a cheap Calibration Weight any day. Unless, they've been recently calibrated, I chuckle when I hear people talk about balance beam accuracy. Anything mechanical can and will be off. I rather put my trust in "two" things that I can prove are pretty "reasonable" than one thing that I'm just assuming is infallible, perfect and idiot-proof.

 

[dmazur]

Unless, they've been recently calibrated, I chuckle when I hear people talk about balance beam accuracy. Anything mechanical can and will be off.

Well, that's why the instructions tell you to "zero" the scale every time you set it up...or if you bump it.

The accuracy people are talking about is the general reliability of a lever. As long as the knife edge and agate aren't damaged (or dirty), and nothing is bent or missing, the balance beam is going to be pretty much the same every time you use it.

This is sharply different from electronic systems that have warm up periods, sensitivity to stray electromagnetic fields, strain gauge aging problems, and power supply stability issues.

And, electronic systems have to be adjusted for "span", or how much weight is shown for a given applied weight, in addition to "zero". Mechanical balances only have to be adjusted for zero, as the span is fixed by the design.

The calibration weights that came with a RCBS digital scale were necessary for that scale. Without them, you couldn't set it up and use it.

However, check weights aren't necessary for use of a balance beam scale. They are reassuring. They tell you that the manufacturer didn't make any mistakes when he made that scale. (And, that nobody damaged the scale since the last time you used it...not a big concern for a solitary reloader without children... )

 

[Steve Marshall]

One of the first things about reloading that concerned me, accurate weight. As soon as I was aware of check weights, I bought some. Lo and behold, balance scales tend to be accurate over the full range. Electronic scales? Not so much. I must be a dorky naif, as I cannot fathom why someone who reloads for a firearm that likely costs several hundred dollars, on equipment that likely costs several hundred dollars, with components that cumulatively costs several hundred dollars, would not spend a fraction of that on check weights and cartridge gages.

 

[Steve Marshall]

Oh, one other thing, coins have manufacturing tolerances like anything else. So weights will vary for many reasons including different materials i.e. copper penny versus zinc.

 

[bullseye308]

If you are gonna use coins, try gold ones. You know they should be right on the money.

If you are cheap like me, take a piece of wire, some snips, & itty bitty baggies to a jewler and cut a piece & weigh it. Adjust till you get the weight you want & bag it. Mark the bag for the weight. Make a range of weights and you are set. No cost involved.

 

[MCMXI]

I've been using a Lyman's check weight set for a couple of years now. I like it because I can bracket any given load within a narrow range.

http://www.midwayusa.com/viewProduct/?productNumber=612694

Example

The 178gr A-MAX load for my .308 Win is 44.2gr of Reloder 15 so before I start dispensing powder I weigh the following combinations of check weights:

20.0gr + 20.0gr + 2.0gr + 2.0gr > 44.0gr

20.0gr + 20.0gr + 2.0gr + 2.0gr + 0.5gr > 44.5gr

I can be fairly confident that my scale can accurately weigh 44.2gr if it outputs the correct values for the check weights.

 

[rfwobbly]

I think tmccray45 missed an excellent opportunity.
He could have named this thread "Change We Can Believe In".

 

[Hondo 60]

very cool - thanks for posting

 

[1SOW]

Pretty soon, our coins will only be worth making in plastic.

Maybe then the 4.0 grain weight will be available for my average load.

 

[TomTerrific]

I was a chemist in an analytical lab and the scales and balances were critical to good lab work. We had a maintenance agreement where they provided service when one malfunctioned and also did preventative maintenance every six months which included an accuracy check.
Having good check weights is an excellent idea.
I have had occasion to purchase scales with 5-10kg limits for kitchen use as well as weighing track and field implements as part of my officiating duties. Accuracy is not as important with kitchen use as one is mainly interested in ratios. I checked two scales out against a certified scale and while both were precise, neither was particularly accurate. However, there was a straight line correlation which I could apply.
That said, a reloader needs to be precise and accurate. You don't want to be putting in ten percent more powder than you think you have.

My two cents.

 

[dmazur]

... a reloader needs to be precise and accurate...

Yes. These terms are often used interchangeably.

For example, if a beam scale got dirty at the knife edges, it might show a loss of precision. Increased friction might make 0.2 or 0.3gr the best that would show, rather than 0.1gr. It is possible, however, that the average of a series of measurements might still be accurate.

On the other hand, if a "chunk" of a poise was removed by accident (say it got dropped on something hard), accuracy would suffer. Given clean knife edges, it could show weights to 0.1gr precision as usual, but all weights would be low due to the missing poise material.

The manufacturer of the electronic scale usually provides 1 or 2 calibration weights to set span (including zero, sometimes this is a 4 point fit), and these are necessary for that function.

They can also be used as check weights to verify that the beam scale is in agreement.

 

[wankerjake]

On the other hand:
Five 55 grain Hornady V-Max bullets all weighed 55 grains exactly.

Yeah I've used bullets to check before as well. They have always been right on. I haven't done extensive testing on this but the bullets I have weighed were consistent with what they should weigh.

Personally I think being consistant is more important than being dead nuts accurate, unless one loads to the max, and frankly I think the powder mfg's have a safety factor built into their data anyway.

But this is just my opinion.

I also agree with this. "weaker" load data helps make up for this as well; old load data for many cartridges and various loads has been reduced over the years. I have a load for my .243 that is just under max in an older manual but over max in a newer one. Never had any signs of overpressure and it is a very accurate load. Not saying that you can assume this is always the case... always work up loads for yourself, yada yada

 

[Mr_Rich]

Precision vs. Accuracy

For those who do not understand the difference, it can be described in shooting terms. If you are both precise and accurate then the average value (distance to bullseye) and the amount of variation would both be small. For example if you have a .25" group and it is all inside the 10 ring.

Precise but not accurate would be a .25" group that is centered 3" to the left of the bullseye.

Accurate but not precise would be a 5" group centered on the bullseye.

I hope this helps everyone to understand the difference.

Rich