Have it checked first by a good gunsmith to determine if it is safe to fire it. You can shoot the " standard" , but NOT the " high velocity" factory 32-20 loads. I don' t think any factory is still making the HV loads, but there are probably some of them still floating around. If ammo you find is not in a factory box with legible markings, DON' T USE IT!! Get a Lyman handbook, and stick to cast-bullet loads that don' t produce more than about 1200-1300 FPS with 100-grain bullets in rifles. These should be safe in a Model 73 that is in shootable condition!