I agree with Wayne - 30-30 shouldn't be fired in that gun. It should also be noted that I see no Nitro proof on the rifle barrel. Apparently, 9.3 x 72 R had different pressure loadings. They had a black powder proof, a nitro proof, and an express proof (Crown E). I'd say that gun has only the black powder proof, and many informed people on the German Gun Collectors would probably not recommend modern loads in it (S&B brand). Plus, SAAMI max. pressure for 30-30 is 38,000 CUP, while the max. for 38-55 is 30,000 CUP. {A generic adage is to use loadings for 38-55 when you load 9.3 x 72R}.

That will help, but he really needs to do a chamber cast to be sure what it really is, and even then it can be difficult to establish because there were proprietory chamberings that are no longer available.