Its a bit tricky to open but it really should be so that the mainspring can be removed, cleaned and lubricated. The barrel lid is not flat but has a side which is a bit different from regular barrel lids. And the lip of the lid goes right down to the barrel teeth.   The lid does come off like any other barrel but because the lip it is quite easy to damage it or the barrel teeth. I usually use a fine stanley knife blade to gently prise it away - the blade should be super sharp in order to get i