Uberti High Wall

[Southpaw]

I posted this in the BROW but will try here also. I purchased an Uberti 1885 High Wall in 45-70 a few months ago and took it to the range only to find it would only fire 3 out of 10 rounds leaving light primer hits. I took it home and cleaned it real well and returned to the range with another manufactures ammo and again it would not fire the 3 rounds I tried,light primer hits. I took to a local gunsmith and he replaced the firing pin spring and test fired 1 round, saying the spring was too stiff. After bringing it home I felt the tension on the back of the block and it is a real light spring. My question is will the real light spring hurt any thing like break the fining pin on recoil or something else.I realize the spring retracts the pin only,so any advise would be appreciated.....Southpaw