I'm not too sure about that. Take a look at these sequential photographs of weighing a nickel on this scale. A nickel should weigh 5.00 grams. On each weigh, I turned the scale off, counted to 10, turned it on and counted to 10 again before putting the nickel on the scale. You can see that the results varied quite a bit.
This might certainly be enough to spot a raw coin of improper weight. It won't help much if the coin is in a slab, though. I wondered if it would be possible to determine the tare weight of a slab and thereby know the weight of the coin inside without breaking it open.
Of course, you first have to know what slab you are looking at. In examining my coins, I found at least half a dozen types and each would have its own empty weigh. In addition to that, some of the styles use plastic fingers to hold the coin - a smaller coin would use more plastic, so you'd also need to account for that.
Unfortunately, the variances in what appear to be identical slabs can be high. These two have a .2 gram difference
The next two I tried were a different style and here the difference was only .09 g, but it's obvious that you cannot expect to accurately determine the weight of a slabbed coin this way.
Given the difficulty of even getting repeatable weights, I'd say this idea is hopeless.
Note: All my coins are in a safe deposit box. I keep nothing in my home.
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