You might visit www.chocolateworld.be and look at their enormous selection of molds, most of which have a weight (in grams) for the finished piece provided. You will find many much less than 13g. The first molds I bought, which were Italian, came from a vendor that does not provide weights, and as there was no easy way of judging the size of a finished piece, I ended up with molds that I now think are quite small, say 10g or less, and those who tried my chocolates found them a little too "dainty." Now I look for molds that are around 15g, which offer--for polite people, at least--two bites rather than one. I myself would not go any lower than 12g and my largest is 18g, but quite a few well-known chocolatiers have single-bite pieces in their collections. To state the obvious, to fill an 18-gram shell takes more ganache than you might expect!