Regarding the breech, you need to make sure pellets are well seated. If not, when closing the breech it can shave / damage the skirt of the pellet. This will also do the rear breech seal no good.
The breech block needs to be firmly pressed down and closed correctly too. They can be stiff so best apply some moly grease to the post below the breech block.
The cocking linkage activates the breech block. If the breech is stiff to operate, it may cause the cocking link to gouge the cylinder in front of the cocking slot.

Issues after that are normal HW ones. If the rifle's new, its most likely dieselling. Strip, clean, relube and a delrin kit should sort it. A good deburr also helps .
Trigger needs to be adjusted properly to give you the best chance of consistency.

Assuming everything is in good order, its then down to pellet selection. I found JSB express worked best in my .177 57 with power set around 10.5

If the rifle's in warranty then you may wish to return to a gun shop. Personally I'd rather have someone conversant with tuning HW's sort it. Lots of talent on here.