If I was worried about wall thickness I would measure them or have a competetent gunsmith measure them. I posted the unaltered chamber end wall thicknesses of several smallbore barrel sets in this thread:
http://www.doublegunshop.com/forums/ubbthreads.php?ubb=showflat&Number=240566#Post240566It includes a Flues with Krupp steel barrels that I shoot low pressure reloads in.
If Gamebore is not publishing the pressure of their loads then I don't think they are under any obligation to make sure their shells meet anything but SAAMI pressures. Do they publish them?
I would be comfortable shooting 8200 psi loads in my Krupp steel Flues.
Best,
Mike