Will upgrading my spring give my gun more range?
Yes and no. Range is dependant on the hop-up unit and it components. For example, if you take a stock gun and put a M110 spring into it the range will increase a little. On the other hand if you take the same gun and replace the hop-up with a better one and upgrade the parts of the hop-up you will see a tremendous leap in range. This can even out range the gun that only had the spring upgraded. The springs greatest effect on any gun is the FPS ( feet per second ) thus resulting in the BB getting to its target faster. The ideal set up for range would be both a spring and hop-up upgrade. So if you are looking for range focus on the hop-up. So yes, upgrading your spring will give your gun more range but how much is dependant on the hop-up. Spring upgrades are more for FPS increase rather than range.

My gun was shooting great when I bought it but seems that it is not shooting as far or as hard now. Why?
Over time and use the lubricants in the mech box break down and thin out. This causes several things to happen. For one the compression in the cylinder has dropped resulting in less FPS and two the gears are encountering more friction which will drop the rate of fire. The mech box needs to be re-lubed from time to time depending on how much you use it. Much like changing the oil in a car, the gun will operate better with fresh lubricant. If you continue with out re-lubing the box you will destroy your mech box just like never changing the oil in you car.

My gun has started “whining “ when I shoot it.
Your motor is not at the right level and the pinion gear in not meeting right with the bevel gear. You will find a slotted or hex screw on the bottom of the handle. Adjust this in or out until the whine is gone. You hear a sharp crisp pop when it is right. Adjust the screw about an 1/8 inch turn at a time, the threshold between right and wrong is very thin.
This screw can loosen from the vibrations created by shooting the gun, to prevent this you can wrap some Teflon tape around the threads. This will tighten the screw and the tape will absorb some of the vibrations. You can find Teflon tape in the plumbing department at Lowe’s or Home Depot.

How can I make my gun more accurate?
The best thing you can do for accuracy is change the inner barrel out for a tight bore barrel. Stock barrels have in ID ( Inside diameter ) of 6.09 and the tight bore barrels drop down to an ID starting at 6.04 and go as low as 6.01. This will greatly increase your guns accuracy and grouping as well as a small FPS increase.

I want to make my gun more silent.
There are several thing you can do to make your gun more silent. The easiest and cheapest way is to replace your flash hider with a foam packed silencer. Now before I go any further with this let me say that this is for airsoft guns only. To put this on an actual fire arm is illegal and two it will blow up and either cause serious injury or even kill you. Now I am not sure about the laws pertaining to an airsoft silencer of this type considering that it will not work on a real firearm but I would check with your state laws first. If you decide to make this item you do so at your own risk and discretion. There are several brands of hollow tube silencers on the market and some of them come with foam in them. The thing to remember is the softer the foam the better the sound reduction. 60% of the noise created by an airsoft gun is generated as the air leaves the end of the barrel. This is the pop you hear when the gun is shot. The foam absorbs this sudden expansion of air and in return muffles the sound. To go a step further you can put an AEG spring inside the foam that will act as an acoustic damper. It’s the same principal as acoustic ceilings,  The surface breaks up the sound wave and dissipates.
The other 40% of the noise is generated by the motor and mechbox. You can minimize the amount of noise by properly shimming and lubricating the box, using a Polycarbonate Piston and piston head, and using a higher end motor. The PDI Rolling Bushings will reduce noise also and if you are going for maximum noise reduction look into a set of these.