I am pretty sure you are wrong. With four immigrant hunters (who start with 25 steel bolts) I was able to melt down the expended ammunition into a bar of steel. There were no other steel objects melted down in that map, so the steel could only have come from bolts.
Hmmm, I smell another experiment!
From the wiki:
"Material size is a property of finished goods. It determines how many units of raw material are required to build or construct the finished good, and how many are recovered when it is melted (if possible)...
...Metal
Material size >= 9 requires 3 metal bars
Material size >= 6 requires 2 metal bars
Material size < 6 requires 1 metal bar"
You're right, my equation was off: when you melt you actually gain a tenth of the material size for that item in metal bars.
bars from melting = (material size/10) x number of items melted
1 = (0.1/10) x 100
1 = (0.01) x 100
So, without going to through the raws, we can deduce that crossbow bolts are size 0.1