I have a .177 npss, shooting the jsb 8.44 @900 fps. Bought this when they first came out.
Original piston, many, many, tins be of pellets have been cycled. Was pellet picky, only liking the the Jsb exact 8.44, with those I could and have stacked 12 shots inside a nickel at 30 yards. Wasn't easy as it was very hold sensitive. In the beginning it was shooting those same Jsb's around 860 fps, the first 3-4 inches of the breech end of the barrel were very tight. I shot it that way for years and decided to lap the barrel to remove that restiction which had three benefits, shooting 40 fps faster and more pellets shoot accurately and not as hold sensitive, jsb 8.44 are still king. I think replacing the trigger would be a huge benifit, as it is heavy. I don't shoot it much anymore, just now and again and my groups have grown as my skills have gotten soft from shooting pcp's. I did change out the shroud by using the nps 2 shroud pieces and and using some hardware store aluminium tubing. Really quieted the crack, really hard to hear the shot from 20 yards, however, next to the ear the mechanical sound is loud. One last thing, I had the issue of galling when cocking. I fixed this by adding old school buttons to the piston. It is very well built, and I still own it after all these years as it is worth keeping around.