hello

common bullet weight's were 16 and 18,2 gramm for the 9x57, here you see some examples

http://forums.nitroexpress.com/showflat.php?Cat=0&Number=217746&an=0&page=0#Post217746

this is the factory ballistic in my 1935 DWM catalog

and this is the 1956 DWM catalog when only the the 16 gramm load was available

because of the long and serpentine history of the Haenel rifle's we put them under Mannlicher Schönauer's most time but please dont worry about. please make some pics so we can see what you have. barrel diameter can be everything between .354 and .358 only sluging the damned thing will tell. whatever the barrel is the rifle was shot in the past with .358 bullets and survive!
there is no problem to load them with .357 mag bullets and I got perfect work in my M 88 with the 180 grains Rem Hollow Point.