Could not resist on CM's 50% offer,had to order one,now here comes the question: Is it a good gun up front or what do i need to do to have a fairly accurate and reliable airgun?
Is the barrel/piston assembly in use on another (whatever is the name ) Air rifle?
Who is CM and what is their 50% offer? 50% gets my attention... While we're at it, what's an NPS 177? Do you mean a TR77 NPS? Maybe a Benjamin NPS? Legit question, I'm not sure what gun you mean.
To answer part of your question though you should clean the barrel before you shoot it the first time. Use Goo Gone on a patch and pull it through with string trimmer line or something similar then use clean patched until the bore is clean and dry. Google/Youtube on how to do that but basically you just fold over one end of a length of line and use heat (torch, soldering iron) to fuse the end back to the line so you have a loop to pull the patch.
Once you do that shoot it a few hundred times before you make any judgements. There are other steps you can take right away but that's a good start. Maybe pull the action from the stock and make sure the pivot bolt it tight and then tighten/locktite (blue) the screws when you put it back.
Very likely the power plant and trigger are the same as many other Crosman/Benjamin guns.