Scale Calibration (on the cheap...)

[sig228]

Ok, so I would rather spend my money on reloading supplies instead of a $34.99 Lyman Scale Weight Check Set. So, all you math wizards, follow me on this:

I want to check the accuracy of my scale using something common such as a penny, so, based on my extensive internet research,

1. ..."a penny's volume is .360 cubic centimeters and the mass is 3.1 grams (pre-1982) and 2.5 grams (after 1982)."

2. 1 gram = 15.4323584 grain

so, a post 1982 penny should weigh 38.580895 grains.

Here's my question: how accurate is this? Maybe someone with a PERFECTLY calibrated scale can do me a favor and weigh a post 1982 penny.

Thanks.

 

[Asherdan]

The one I used weighed 38.6 so I guess your math is pretty spiffy. Buddy check weighted his scale and weighed off a post '82 penny for me and I used it a few rounds of reloads until my check weights showed up in the brown truck.

Which I then used to zero and confirm the penny was A-OK on.

Lotsa variables, though. How grimy is each individual penny? How much wear? I used a clean and almost unworn one.

I still say this is a better option. I like to rezero with the check weights at or very close to the charge weight I'm working with. Probably doesn't matter and maybe good enough is OK 'till I prang a gun and/or myself with a powder boo-boo.

 

[sig228]

LOL... I expanded my search back to 2005 and this topic was actually discussed:

http://www.thehighroad.org/showthread.php?t=166546&highlight=scale+calibration

Seems like they were coming up with 38.8.

Asherdan, thanks for checking.

 

[moosehunt]

No way something as crude as a penny is really going to be accurate, but we ain't building a watch! Those $35 check weights aren't very accurate either. Your penny approach method is probably nearly as good as those cheap check weights, plenty good for our crude weighing in reloading, and as you so astutely observed, considerably more economical. Our reloading balances don't have the precision (or accuracy) to do any better anyway.

 

[rcmodel]

You can use a jacketed rifle bullet from any of the name brands.

If you weigh a 50 or 150 grain rifle bullet, it will weigh 50 or 150 grains, or close enough for government work.

Well, it actually may weigh 149.9, or 150.1, but it will still be cloaser then just any old penny.

Whos to say how much weight is worn off of a 28 year old penny just from handling it.

rcmodel

 

[zxcvbob]

Use a nickel instead of a penny for a checkweight. (I'll have to look up the weight; I don't have it handy) They keep changing the formulation for pennies. Also, the alloy used for nickels is more durable so you don't have to worry about how much it has worn down (I'm not convinced that this really matters).

 

[Walkalong]

so, a post 1982 penny should weigh 38.580895 grains.

Here's my question: how accurate is this?

Check it with your scale.

I have no idea.

 

[cougar1717]

I think RC's got it right. When I first got a digital scale, I weighed out a few boxes of bullets just to see the tolerances of different manufacturers. A whole box of Sierra rifle bullets will usually have a spread of .4 grains and a mean that is the exact bullet weight (150.0gr for example).

 

[Asherdan]

Y'know, the OP didn't say if he was using a balance or digital scale. I could see a known weight item being used for a digital to check calibration. I use a balance so I like having a check set so I can confirm it's good right at my common charge weights of 10, 12, 20.5, 51. Using the check weights to set the balance lets me consistently drop the same (within the tolerance limits of the balance) charge weight from session to session. I can tell when I started doing this from my reloading log, lot to lot performance tightened up.

 

[ranger335v]

Sig, I understand your desire for "accuracy" but believe it's misplaced a bit. Repeatabllity, or consistancy is what we really need from a powder scale.

If we/you develop a load with a given scale, and it shoots well and is safe, it really doesn't matter if the charge is actually, let's say 45.2 gr. or 45.8 gr. IT IS VERY MUCH NECESSARY THAT THE SCALE BE REPEATABLE THO! I mean, it must consistantly measure the same charge the same way everytime time you load a batch.

Most reloader scales are quite consistant. You can monitor and confirm yours by making your own "check weight". Simply weigh a penny, nickle, bullet or a nail and use it to confirm that your scale is consistanly reading the same over time.

I have a piece of brass I weighted when I bought my first scale in '65. I marked it for 255.4 gr. The same scale still measures it exactly the same. If it's off a bit in absolute accuracy I really don't care.

 

[langenc]

Instead of check weights someone who posts could weigh penny, nickel, quarter and half(new ones) and then everyone could have a set.

Couple others verify and we are good to go-Lyman out of business w/ weights.

 

[rcmodel]

On my electronic scale, I use the pan itself as the check weight.

With the scale calibrated & zeroed, take the pan off and note the minus weight.

My pan weighs 81.7 grains, and if I get a minus 81.7 reading with the pan off, the scale is repeatable every time I use it.

I weighed & wrote 81.7 on the bottom of the pan three years ago when I got the scale, and it still weighs 81.7 when the scale gets up to operating temperature.

rcmodel

 

[Ol` Joe]

Why not clip a couple various lenghts of copper wire of different ga and ask a jewler to tell you what they weigh? His scales are not in grains but, can be converted and they are regularly checked for accuracy to goverment standards.

 

[brickeyee]

If you are not actually calibrating an electronic scale or balance beam, all you need are some objects of known weight that cover the span you are interested in.

They are 'check' weights to ensure the device is still operating properly.

Digital scales often need the specified weights to perform the calibration of the strain cell.
Any value could be set in the software, but we are usually stuck with the manufacturer's choices.
Some lab scales DO allow the programming of different cal weights, but think $$.