if you cycle the slide by hand, will it re ####? If so, you may simply need to try a different ammo. If not, you probably have a trigger problem, and you'll need a good smith. The other possibility is that the spring could be worn out and it's slamming, and the hammer doesn't have time to engage the full #### notch. Wolfe gun springs can supply a new spring set, and will ship to your door. It's a good idea to replace them all anyways if you don't know the history of the pistol
FYI It shouldn't be fed high velocity ammo. The stock springs are for standard velocity rounds, and a steady diet of high velocity fodder will batter the slide.