See if the spring follower plunger has any unusual wear marks on it as well as the end of the spring that rests on it. The spring may be trying to push by the side of the plunger if its undersided enough. I've seen that happen with shotgun mag tube plugs. If you take just the plunger and drop it down the tube does it make it all the way to the bottem, or does it get hung up? I'd also try seeing how the binding is with the hammer removed just to rule that out.
Its been a number of years since I've taken the recoil spring out. If I remember correctly there is an right and a left hand spring one inside the other for the recoil spring. the different directions they are wound keeps them from binding up.