Where are you saying the Magtech brass is too thin? Is it for the purpose of swaging the rim or for holding the "Valve"? I could turn the rim so that would not be a problem. If there is not enough Meat to provide strength enough to hold the cap adapter that would another matter.
The Magtech case is a very thin walled 'baloon head' type of construction.
Also it doesn't use a 209 primer.
A fellow could simply drill the base of the primer pocket and tap some suitable threads in the primer pocket walls and thread in a plug, then cross drill the firing pin hole.
As noted above, the case walls are thin and if the percussion cap is nested against the inside case wall opposite the externally protruding firing pin the case can dent from firing pin strikes.
