When trying to determine the actual amount of silver in a weighted sterling piece, it helps to have many examples upon which you can rely regarding true silver content. Here's another.
The picture below depicts a Reed and Barton weighted sterling candlestick - on the left is the original candlestick and on the right is the weighting material after the sterling casing was removed.
The original candlestick weighed 228 grams. The weight of the sterling outer casing after being removed weighed 28 grams. So, only 12.3% of the weight of the original piece was sterling.
If you try to remove the sterling casing from a piece like this, you might be interested in the picture below. The nails form a support for the weighting material, somewhat like rebar rods inside concrete. Be careful!