Hello Johann - the 1899-vintage Rigby .400/.350 Nitro Express was one of the more popular British sporting rounds in Africa before WWII according to John Taylor. Ballistics were a 310 grain bullet at 2100 fps and it had a very good reputation even on large and dangerous game. I have always wanted a nice single shot chambered for the .350. That old ammunition you have ought to be worth a fair amount also.