Rregardless of calibre the magazine is .22 so .177 pellets fit loosely and you have to be careful when loading not to crush or get them stuck in the breech.
Open sights are quite good, there are 11mm grooves to fit a scope but they are not great, a small red dot sight works well.
Criticisms of this gun would be the effort to pump and you need good technique so as not to twist the lever. the trigger gets correspondingly stiffer as you increase the pumps but the trigger is predictable. On the plus side it is light , has no recoil, the stock is comfortable and overall I think it looks good. Accuracy is very good.
Below is a picture of the gun in action and a strip down guide below that.