Matching hk finish in cerakote is a pain... it's not easy to
Get the same consistent finish in the blacks. Back to back to back.
Hk duracoat is a lot easier to accomplish this and is more of a correct finish.
The only time I prefer dura to cera...
As far as the mag wobble... without seeing it, it could be as easy as swapping the mag catch with a factory hk catch.