Hi, Southlal and guys,
Sorry for the misunderstanding. I meant that the floorplate should not come off in firing, not that it can't be removed. The GI floorplate has two little dimples at the back and one at the front. These keep the floorplate in pretty solidly. Removal is by prying up at the front, and sliding it off. But the floorplate is not spring steel and if this is done very often, the floorplate will take a permanent bend and not lock into place.
Some aftermarket mag floorplates do not have the rear dimples, and some have none, depending only on the end edges and the folded sides to keep them in place. These can come off pretty easily.
As might be gathered from the above, I do not recommend taking carbine mags apart for cleaning on a routine basis. If possible, simply slosh them around in a cleaner rather than removing the floorplate. Nor do I recommend replacing springs. I have GI WWII mags whose springs are perfect, although I do not leave them loaded. IMHO, there are just too darn many people replacing springs without any idea what they are doing or why.
Jim