Hi, I have several Hollenbeck drillings but I’m not a smith. Do you know what caliber the rifle is, sometime you can find the caliber stamped on the lugs or barrel flats.
Looking at the internals it appears(and I’m guessing) the springs are missing for shotgun hammers.
You need to reach out to a gentleman named Tom Archer. I personally think he is the most knowledgeable person on everything Hollenbeck/Syracuse/Three Barrel and Royal Gun Co.
Carl