How far can it shoot stock? Well, they don't have velocity adjustment on the older models, and they are supposed to be set at around 250 fps, depending on the weather of course. Mine has been up to 295 fps on a hot day, and with a velocity adjustor that's no problem. So they shoot as far as a paintball will travel at whatever fps you desire.
Good practice range though I find to be about 50 feet or so. You're going to want to get closer when playing with 12 grams so that there's a greater chance of the ball breaking, so you don't take as many long ball shots. At least I don't.
Getting the 12 gram out, basically I don't change that til there is no more paint in the gun. I get a 12 g and a tube of paint ready before I change, pump the gun back, unscrew the cap, pop in a new 12 gram, screw it in, pump it back forward, fire the priming shot and load the paint.