your "collath" case looks great, mister collath himself would be proud. this firm chamber the 8x57R 360 , 8x57IR, 8x72R Brennecke and a special 8x72R Collath-Teschnerin the own guns. the last one looks like adown sized 9,3x72R Sauer&Sohn but is in the class of the 8x57R360, I suspect a lower pressure for building Drillings again ligther.

I read the stamps on your drilling this way: C.4=8m Mod.88 - Collath shotgun No.4 8mm Mod.88 is 8x57 IR

if so I have no fear to shot modern 16 ga ammo in it but would make a chamber cast of the shotgun barrels to see wich shell length can open up without problems