Sounds like not a strong enough mainspring, OR something is slowing down the hammer's fall. Or both.
If you can strip it completely apart, consider fine-polishing the sides of the hammer and the channel it rides in, to reduce friction. This is NOT the same as a "trigger job" and trigger feel won't be significantly changed. This lets more mainspring energy end up on the firing pin. Unless you know what you're doing, avoid messing with the sear surfaces in any way, shape or form.
A simpler solution is a heavier mainspring, but this will of course increase trigger pull weight and cocking stroke pressure. Putting the sweat equity into fine polishing internal parts and reducing friction will yield a better gun than the factory was willing to put the effort into.
No guarantee that polishing will eliminate light primer strikes but it can't hurt. You can always find stronger mainsprings through Wolff or the like (probably the same as what an Uberti percussion open-top would use, but I'm not sure about that).