New to reloading question

Could be how they are positioned in the tray. You need a set of check weights.. they are very inexpensive.

Coins are not reliable check weights.
They only have to be close enough to work in vending machines and parking meters.

Wear, new sandwich coins vis real silver coins, and variations through the years make it impossible to use coins as reliable check weights.

The best Field expedient check weight I know of is factory jacketed bullets.

If Hornady or Sierra or Speer sells you a box of 55 grain .224" bullets?
You can go to the bank it weighs close enough to 55 grains for GooberMint work.

The only problem is, accurate at 55 grains doesn't mean it is accurate at 3.5 or 5.0 or 23.5 grains.

You really need a set of check weights if you really want to worry about RCBS's calibration being 100% right at all ranges of the scale.

rc

rcmodel said:

Coins are not reliable check weights.
They only have to be close enough to work in vending machines and parking meters.

Wear, new sandwich coins vis real silver coins, and variations through the years make it impossible to use coins as reliable check weights.

The best Field expedient check weight I know of is factory jacketed bullets.

If Hornady or Sierra or Speer sells you a box of 55 grain .224" bullets?
You can go to the bank it weighs close enough to 55 grains for GooberMint work.

The only problem is, accurate at 55 grains doesn't mean it is accurate at 3.5 or 5.0 or 23.5 grains.

You really need a set of check weights if you really want to worry about RCBS's calibration being 100% right at all ranges of the scale.

rc

Click to expand...

RCModel, I think you mis-read the OP (or I did).

He weighed each of three coins. No matter if they weighed the same as each other or not. They weight what they weight.

He then added the three numbers together

Then he weighed all three coins together (same coins)

The combined weight did not equal the sum of the three weights.

That adds up to a scale that needs attention of some kind in my book.

You (very correctly) stated

The only problem is, accurate at 55 grains doesn't mean it is accurate at 3.5 or 5.0 or 23.5 grains.

Click to expand...

and that seems to me to be the crux of the O.P.'s question.

On the other hand, .3 grains is not a large variation when you consider it as a percentage of the measured weight. (Coins are a lot heavier than most powder charges).

If I were the O.P. I would get a few toothpicks or dried beans or something close to the weight of my anticipated powder charge and perform the same calculation. That way I would be testing the consistency of the scale through the range in which it will be performing for me.

Note: These toothpicks or beans would not be check weights over any period of time. I would not expect them to refrain from absorbing water from the air or getting eaten or used.

Lost Sheep

O.K.!

I see now what you said was not what I thought I think I read.

Never mind!

Go back and make sure the table the scale is setting on is perfectly level front to back with a carpenters bubble-level.

Then make absolutely sure neither end of the knife edge bearing on the beam is rubbing on either end on the base bearing stops.

Then zero the scale with the screw in the base.

Then run the repeatability tests again.

rc

rcmodel said:

O.K.!

I see now what you said was not what I thought I think I read.

Never mind!

Go back and make sure the table the scale is setting on is perfectly level front to back with a carpenters bubble-level.

Then make absolutely sure neither end of the knife edge bearing on the beam is rubbing on either end on the base bearing stops.

Then zero the scale with the screw in the base.

Then run the repeatability tests again.

rc

Click to expand...

Yes, good point, RC, and while you are leveling the scale fore and aft, make sure it is OK side to side as well. And stable. If you have an eye-level shelf or cabinet top, it will make it easier and more repeatable to read, as well.

Lost Sheep

Hi

- Weighing three coins independently vs. together increases any error by 3X.
- The resolution of the scale is 0.1gr so it cannot weigh more accurately than that. This means that worst case you can have an error in the scale or parallax error of 0.1gr that would multiply to 3X. Apart from the advice on levelling already offered I would offer the following;

Is your eye in direct line with the marks on the scale beam pointer, you could have a parallax error.

I have just duplicated your exercise, with the same scale, paying particular attention to avoiding any parallax issues.

Coins individually 61.4 + 61.1 + 61.3 = 183.8gr.
Coins together = 183.8gr.

Hope this helps.