Although I do not know the specific details about the KA mag catch problem, may I suggest slightly enlarging the catch slot with a file.
Very sweet kit by the way.
TM SR-16 *Stock*, And A Shitload Of Mags
Apparently, a hand grenade does not belong in my toolbox. Nor does a hand grenade with the pin pulled belong in someone else's toolbox.
When In Doubt, Empty A Magazine.