As far as i know, all chem weapons do indeed damage armour, if the damage inflicted passes the treshold, so rounding down would result in at least 10 / 1 damage.
Also, the melting happens for each shot or pellet, so naturally single shot chem weapons arent really efficient if your aim is to reduce armor. I.e. Magnum Chem is powerful, but not efficient if you want to break down armor. A weapon like the Blunderbluss with Chem Ammo however is very efficient at Stripping armourm due to the amount of shots it fires even on snapfire.
In general however, breaking down armour of Mercs and Marsec is not really that useful to me, because the treshold for it to be worth it is so high (i.e. reduing armour from 90 to 80 is not really helping you ata ll).
Better just use a bunch of gauss muskets or heavy gauss in the first place it probably the more efficient approach if you consider the total TU usage to bring one down compared to using a handful of chem shots.
Or just use RPG with HEAT.
