Calibrate vs. zero

[Quoheleth]

I was reading the thread on checking the powder scales (http://www.thehighroad.org/showthread.php?t=448754) and the thought occurred to me: what ishould the reloader be more concerned about - a calibrated or zeroed scale?

I check my scale (Lee) for zero before I weigh anything and make sure it reads 0.00 and the balance is right on the line. Sometimes I have to make a minor adjustment to the brass wheel, a little bump in or out, but not much.

Calibrating means taking a fixed, known weight and checking to see what the scale says it weighs. Theoretically, a zeroed scale will weigh the known weight precisely at its weight point. What if the numbers don't agree, though? Let's say the weight should be 5 grains, but the scale reads 5.5 grains and is zeroed perfectly. Then what?

Q

 

[Ol` Joe]

As long as the scale reads the same every time the object is weighted you`re fine. The powder charge you use should be worked up from a lower wgt and if done properly as long as your scale brings you back to the weight you had when you decided on a load you are OK. It doesn`t really matter if the load is .2gr off for instance from a calibrated scale.

 

[Shoney]

Sets of Check Weights are available that will help calibrate a scale.
You zero the scale, then set it to X grains and test the accuracy of the scale with the various check weights or combinations of check weights.

If the scale is off, you can make a listing of what setting equals what weight.
I.E. If the 100 grain check weight shows 95 grains on the scale; and the 10 grain check weight shows 9.5 grains on the scale; and the 1 grain weight shows 0.9+ grains. You have calibrated your scale. You know that the weight shown on the scale is 5% less than actual weight; or in mathematical terms

scale reading = actual weight desired - 5% actual weight desired.

 

[ranger335v]

Unlike flaky digitals, a beam scale ONLY depends on gravity for its accuracy. That does not change over time, so the scale won't change either. But, the ZEROING of any scale is the foundation of accurate readings! If your zero is off by .5 gr. you will be off by .5 gr. across the board. Calibration would require adjusting the scale to be accurate at each point on it's adjustment range.

As Ol' Joe points out, within reason, the calibration, or dead-on precision, is of little concern to a reloader. What we MUST have is dead-on repeatabliity! Meaning, will a charge we weighted at a certain amount ten years ago be the same as if it were weighted today? Most commonly, it will be. If so, our reloads will also be the same, for as long as we use the same scale!

What can change is the repeatability. If we allow the pivot bearing rod/knives to rust, get burred or dusty dirty, or if we allow the beam to slip so the pivot bar rubs on the clips holding the bearings in place the scales reading WILL vary. But, keep the bearings clean, knives sharp and free of end rubbing and it will serve forever.

I know a few guys who have bought the moderately expensive "check weight" kits over the years. No one says they have done a thing for their handloading. Seems a quality bullet used as a check weight will do about as well as anyone really needs to confirm the "accuracy" they need.

 

[MCMXI]

I know a few guys who have bought the moderately expensive "check weight" kits over the years. No one says they have done a thing for their handloading.

Clearly they've done something for me and without them you're just guessing even if your beam scale is "zeroed".

http://www.thehighroad.org/showthread.php?t=433321

Regardless of what system you use to weigh powder, if you aren't using accurate check weights then you have no idea if your beam or digital scale is linear let alone accurate.

Isn't a charge WEIGHED rather than WEIGHTED?

 

[Randy1911]

Like you I "zero" the scale every time I use it. However, my RCBS 10-10 scale with a one check weight, a 250 grain weight. So far, if I zero it correctly it weighs 250 with the check weight. You can buy a set of check weights. MidwayUSA sells them http://midwayusa.com/Search/#check weights____-_ and I am sure others do to.

 

[ants]

Which one should you do?

Both.

Those are two different procedures. Do both. One is for accuracy, the other for precision.

The calibration is of little concern to a reloader.

Maybe little concern to you, but This Reloader cares A LOT.

He has been reloading for 41 years, with several scales, and he wants to know that his notes mean what they say.

 

[rcmodel]

+1

A scale that is perfectly zeroed, and repetable, but off by 1/2 grain is no use to me at all.

.5 grain is nearly a 20% error on a 2.7 charge of Bullseye!

rc

 

[MCMXI]

been reloading for 41 years, with several scales, and he wants to know that his notes mean what they say.

That's where I'm at. All of my loads are referenced to a known STANDARD. If I need to replace one of my digital scales, or if I'm on a hunting trip or match away from home and need to reload using a friend's (or stranger's) equipment, all I need to do is weigh the check weights to "calibrate" my data to a different scale. I think it's good insurance for $35.

 

[MCMXI]

A scale that is perfectly zeroed, and repetable, but off by 1/2 grain is no use to me at all.

But if you know it's off by 0.5 grains (by using check weights) then you can adjust accordingly. A scale that is "perfectly" linear but offset by 0.5 grains is fine by me since that's easy to adjust for. Linearity is much more important to me because it's an easy workaround. Non-linear systems are a PITA!!

 

[rcmodel]

but offset by 0.5 grains is fine by me since that's easy to adjust for.

I make mistakes balancing my checkbook.

God forbid I had to do math in my head to know what my scale really reads every time I used it.

rc

 

[Shoney]

rc
Thats why pencils have erasers. Like 1858 said, it's easier to figure linear, and it's much easier to calibrate by using simple math.

 

[Matt Dillon]

I for one don't care if you all use check weights (but those that don't, I hope you're not shooting next to me at the range), but I start every reloading session by referencing one of my check weights on the Ohaus 10/10.

 

[Shoney]

A very important point to remember with check weights. They should be handled with tongs/tweezers so oils from your skin do not get on them.

I took my check weights into a chem lab at my university and weighed them. The Metler Ballances could actually weigh finger prints. I'm sure one or two finger prints cannot be detected by even the best powder scales, however, the brass check weights will absorb oil over repeated handlings. They can probably be boiled out, but they certinly cannot be wiped off, as I found in my testing over 3 years.

 

[Otto]

What if the numbers don't agree, though? Let's say the weight should be 5 grains, but the scale reads 5.5 grains and is zeroed perfectly. Then what?

Then the scale has failed. Throw it in the dumpster or send it back to wherever it came from. Just because a scale holds zero don't mean squat.

I would never use a scale without first verifying it's accuracy with check weights.

 

[ranger335v]

"A scale that is perfectly zeroed, and repeatable, but off by 1/2 grain is no use to me at all."

With your illustration, no contest at all and none of us should be careless of scale accuracy.

To the best of my knowledge only a digital scale with an improper tare function would be consistantly off across the board, high to low end. When I said "consistant" in reference to error I meant that we could count on that level of error (usually found as a percentage of the reading), not a consistant off-set across the range, such as 1/2 grain off across the board. However, if an accurately developed charge reads 55.8 gr. on the loaders scale but is actually 55.3 gr., the error matters not IF that charge will always read 55.8 and shoots good. Please note that I specified "within reasonable limits" the dead-on "accuracy" isn't critical, and it is not, but the example of some 20% error is NOT reasonable!

No such error is possible with a proper reloading beam scale unless the beam has been damaged in some way. And damage to that degree would be, or certainly should be, clearly visible so the user shouldn't be caught off guard, as he would be with a simular error on a digital scale!

I know of no one who has used a set of check weights that has ever found his scale to be off more than a few tenths and even that seems uncommon. But what can, or even should be done about it, if a scale is "off" a half grain at maybe 100 grains? Does that half percent of error really matter so long as it's consistant?

Consider that a loader properly develops a load while using his own scale and finds a "max" load for his rifle. Afterwards he only needs stay at or under that reading when using his own scale, even if its absolute accuracy IS off a bit! As long as his scale is repeatable he will remain safe, his charges will be consistant and that's all he needs.

He might not be safe going to a friends house and loading his chosen charges on his friend's scale, especially if his friends scale is off a bit in the opposite direction, but surely that's quite rare! That's what I mean when I say it's not necessary to be absolutely accurate while repeatablity IS absolutely necessary.

My experience with scales of various mechanical types has been that any error is - usually - pretty well linear. If a scale is 2% high at one end it will be so across the board and that can be confirmed with check weights. Anyone who KNOWS his powder scale is off by any given percentage can easily calculate the error for any charge but such corrections really aren't needed so long as he loads with that scale each time he goes to the bench.

Casually swapping powder scales around is NOT repeatable!

 

[Historian]

Because of the size of my loading bench, it is necessary for me to move my scale a bit after charging fifty and before seating them. As a result, I zero my 505 and check weight it every time I start a charging run. This might mean three or four cycles an evening. I would not want to start charging without zeroing my scale an then confirming with a check weight. +1 for handling weights with tweezers.

Historian

"Democracy requires wisdom."