I looked and didn't find anyone selling a 2/3 teaspoon, looks like the standard spoons are .5 and then .75 ... I'm just going to take a 3/4 teaspoon and put a few drops of wax in it to get the measurement, and then see if I can seal it with nailpolish. I do wonder if the cylindrical shape of the Lee dippers or a say .38 Special case might measure more consitently than a spoon.
I'd go with 1/8 tsp, in decimal 0.125 tsp, 0.125 tsp x 5 cc/tsp = 0.625 cc, and fill that. Also, I searched and it is possible to find 1/16 tsp measuring spoons, about 0.3125 cc.
1/4 tsp is about 1.25 cc
1/2 tsp is about 2.5 cc
3/4 tsp is about 3.75 cc
For the Lee published VMD of Win 231, those would be (rounded to tenths):
1/16 tsp is about 3.4 grains
1/8 tsp is about 6.7 grains
1/4 tsp is about 13.4 grains
1/2 tsp is about 26.9 grains
3/4 tsp is about 40.3 grains
1 tsp is about 53.7 grains
BTW, I keep using "about" because a teaspoon isn't really 5 cc, it's 4.928922 cc; a 1.42% difference. For nutrition info on the side of food, they use a 5 ml teaspoon, a cubic centimeter being exactly the same as a milliliter, but that's not what a real tsp measure will hit. (They use a 15 ml tbsp, etc. Scientists, food scientists included, do their work in metric, so it's just easier for them to use an exactly 5 ml teaspoon. Food doesn't generally combust explosively however, so confirmation with a scale is 100% needed.)
I don't think cylinders are better than spoon shapes for measuring dry goods if used properly (consistent and repeatable scoop action, scrape off the excess, all that stuff) FWIW.