I'm sorry to say that the majority of internal upgrades do little to no good at all. Your distance will be entirely controlled by the velocity you shoot at. There is the Apex or Flatline barrels that in a sense increase your distance, but they don't increase your effective
range. That is to say that at any given distance your paint will still be traveling the same velocity. With the barrels mentioned, your paint just flys at a flatter trajectory - good if you don't want to deal with arching your shots. Regardless, the vast majority of reasonable shots will take place within 150 feet which you can definitely reach with a normal barrel.
As for accuracy, you chose a fine barrel. There isn't really that much difference in accuracy among aftermarket barrels. As long as they are decently made, they all shoot relatively similar. And you're using HPA, so your shot consistency will be good. That's about all anyone can do to make their marker accurate, all that is left is practice.
Most aftermarket internals don't live up to their marketing claims. Sometimes they cause more problems than they solve. Generally the more you have to upgrade something the more it was lacking in the first place. Have confidence in your stock internals, BT makes a good marker. The only truly useful internal upgrade would be a metal power tube in the event that you plan on running straight liquid CO2 - but that is an entirely different story.
That said, a spring kit isn't a bad idea. They allow you to adjust how hard your hammer hits the valve, and can really increase your air efficiency. Ideally you want the lightest spring possible that still allows you to shoot your desired velocity, and your stock velocity adjuster turned out - doing as little work as possible.
This post has been edited by Piller: 14 February 2010 - 10:53 AM