Smith and Wesson Highway Patrolman

[ntfdlt04]

I have a Smith and Wesson Model 28-2 Highway Patrolman that I purchased from a friend over the summer. I havent shot it much, but last time I did, I noticed that roughly one round in each cylinder full misfires. The primer have a light pin strike on the rounds that misfire. This so far has been isolated to one type of ammo. Ive read that the mainspring could be tightened up or maybe its the ammo? I havent had a chance yet to try another box of a different kind. Any suggestions or opinions are appreciated.