Shoot it more!
Really though, it isn't really even broken in until you get around 500-800 rounds thru it. It'll probably loosen up a bit. The length has something to do with it as well. What barrel length do you have? The reason I ask is because the shorter one, like I have, has a captive spring whereas the longer ones, that I haven't seen, may have a guide rod. It sounds like that is what you have because you changed it out. The amount of force required to operate the gun efficiently is there for a reason. I'd consider some hand exersizes. I don't say that to be mean, because after I broke my left wrist, I had a hard time, so I worked on my grip and now it's all good.