First, it's NOT okay to dry fire. Spring piston guns are kinda like compound bows........they need resistance to cushion the power stroke. Spring guns are very hold/rest sensitive compared to compressed air guns like your Sheridans. Variations in how you hold your rifle or rest the forend can change the POI and scatter pellets. Consistency is key. Also the weight and type of pellet can make a big difference, I haven't seen too many high powered spring guns shoot light weight pellets well.
