You may find this article interesting: http://www.coinweek.com/featured-news/coin-rarities-related-topics-unique-1873-cc-no-arrows-dime/ Per the article, weight specifications for US coins were revised in 1873 from grains to grams (see text about 1/4 down the page). This remained in effect until 1964 when the US quit using silver in dime and higher value coins. The specifications for the new alloy coins were in grains. Per the Mint, the penny and nickel are metric, 2.5 and 5 g. Dimes, quarters and half dollars can be converted but are really specified in grains, and any mixture of these three coins work out to $20/lb. The dollar coin is lighter, relative to value, at $56/lb. Althoughly slightly before the big push for metrication in the 1970's, you have to wonder why they chose to go back to grains after 90 years of metric practice. What WERE they thinking?
